version 2.4.4

trs80gp - A TRS-80 Model 1,2,3,4,12,16,6000,DT-1,Videotex Emulator

trs80gp primarily emulates the "gray" line of TRS-80 computers made by Tandy in the late 1970s and early 1980s. They are known as the Model I, Model II, Model III, Model 4, Model 4P, Model 4D, Model 12, Model 16 and Model 6000. It is generally easier to use ordinary digits for the Model 1, Model 2 and Model 3. The Model 1, 3 and 4 are a line of compatible computers as is the Model 2, 12, 16 and 6000.

Also emulated are the TRS-80 DT-1 Data Terminal, TRS-80 Videotex and the Electric Crayon external colour display.

The emulator runs on Windows from XP all the way up to Windows 10. Included in the download are versions for MacOS, Linux and Raspberry Pi. They may not be at full feature parity with the Windows version but the emulator runs just fine under Wine. It should run well on any machine produced in the past decade.

trs80gp provides accurate and near complete emulation with excellent programmer support. The source code is fully organic and hand-crafted by myself and my brother Peter.


Bug reports, feature requests or other inquiries about the trs80gp emulator are best e-mailed to me (see bottom of this page for the address). There is a community of TRS-80 users still out there who can help with questions operating the machines (in both emulated or physical form) and even some amount of expertise on trs80gp itself.

I've recently created a trs80gp Facebook group and a trs80gp Discord server as venues for more interactive discussion. You may not find many people there but I will keep an eye on them myself.

The most active TRS-80 forum is the Tandy Radio Shack section of the Vintage Computing Feduration forums. There is also a somewhat less busy Tandy Computers forum on AtariAge and a very lightly used TRS-80 subreddit. There are also a handful facebook groups dedicated to the TRS-80 models that trs80gp emulates.


The emulator is still a work in progress. Much needs to be done to perfect the Model 2 timing and screen effects. Some obscure Model 3 and 4 video effects are not accurate. Videotex and Electric Crayon don't have a full slate of programmer features.


By default trs80gp comes up in Model 3 mode with a full 48K of memory and all supported hardware attached. Command line arguments are used to select different models, hardware configurations and startup options. Run "trs80gp -?" or use the "Help → Command Line Options..." menu to get the latest information on them.

Programs can be run directly on the command line. Doing so loads them much faster than reading from virtual cassette files and without the hassle of writing them to a virtual disk image. Files in "DOS" format (.cmd) are run at the TRS-DOS prompt. Other machine language files and BASIC programs are run at the ROM BASIC READY prompt or at machine boot for Model 2 and 4P which don't have a ROM BASIC.

It may not be obvious that this direct running of programs is not the way the TRS-80 normally loads and executes programs. Some programs may not work especially disk BASIC programs. However it is very useful for program development and is otherwise extremely handy when it does work.

To give it a try, download the emulator and also my bouncing ball demo program. You can run it directly from the .zip archive:

Which will prompt for which file to use. Or specify the file inside the .zip archive directly like so:
Or you can extract the virtual cassette file yourself and run it:
      trs80gp ball.cas
You can load machine language programs in .cmd, .hex and .bds formats. My Z-80 cross assembler zmac produces all three formats and with .bds you get full source-level debugging (see Debug → Z-80 Debugger... and Debug → Source Code...).

It also can load BASIC programs in tokenized form or plain ASCII.

There's so much more! But I'll leave it at that and spend the rest of this page more in "reference manual" mode.

Command Line Option Summary

Hardware Selection
-m1Emulate Model I
-m2Emulate Model II
-m3Emulate Model III (default)
-m3nEmulate Norcom Model III clone that fit in a Model I case
-m4Emulate Model 4 (same as -m4a)
-m4aEmulate Model 4 with 2 wait states per instruction
-m4bEmulate Model 4 with 1 wait state per instruction
-m4cEmulate Model 4 with no wait states per instruction
-m4gaEmulate Model 4 Gate Array
-m4pEmulate Model 4P
-m4ssEmulate Model 4 Student Station
-m12Emulate Model 12
-m16Emulate Model 16
-m6000Emulate Model 6000
-mdt1Emulate DT-1 Terminal
-mvEmulate Videotex Terminal
-mecEmulate Electric Crayon
-l1Run Level I BASIC ROM (Model I or III)
-l2Run Level II BASIC ROM (default) (Model I or III)
-rNUse ROM revision N (-r0, -r1, -r2, ...)
-nlcNo lowercase for Model I
-nldDo not load Model I lowercase driver from cassette
-altUse alternate character set
-charrom fileUse character generator ROM from file
-50Set frame rate to 50 Hz
-gXHires graphics: -g0 none, -gt Tandy, -gg Grafyx, -gc Grafyx clone
-gtp for Tandy with fixed PROMs for Model 2,3,12,16,6000.
-ddTYPESelect Model I floppy doubler: -ddx none, -ddp Percom,
-ddr Radio Shack, -ddrp RS+Percom, -ddd detect at boot)
-dxDisable floppy disk controller (boot into ROM BASIC).
-hxDisable hard drive controller
-mem nEmulate n KB of RAM
-mem16 nEmulate n KB of 68000 RAM
-memgap16 b nUnmap an n KB gap in 68000 RAM starting at KB b
-mmu16 bitsSet number of extension bits in 68000 MMU (default 3)
-rom fileUse ROM image from file
-aftAculab floppy tape (Model I only)
-80-grafix80-Grafix hires character generator (Model I only)
-80-grafix+80-Grafix+ hires character generator (Model I only)
-pcg-80PCG-80 hires character generator (Model I only)
-80-grafix380-Grafix3 hires character generator (Model III only)
-omikronOmikron Mapper for Model I (for Omikron CP/M)
-omikron-aOmikron Mapper using version A ROM
Program/Media Selection
-c file.casInsert cassette file.cas
-w file.tapeInsert floppy tape wafer file.tape into next free drive
-dN file.dskInsert disk into drive N (0,1,2,3)
-d file.dskInsert disk into next free drive
-d dmkInsert unformatted disk into next free drive (.dmk format)
(add -ds for double-sided and #N for tracks)
-d imdInsert unformatted disk into next free drive (.imd format)
-d :nameInsert internal diskette ":name" into next free drive
-tdBoot TRS-DOS (default)
-ldBoot LDOS or LS-DOS
-d0 -Don't insert TRS-DOS disk
-h file.hdvAttach hard drive to next free slot
-hN file.hdvAttach hard drive to slot N
file.dskInsert disk into next free drive (also .dmk, .imd)
file.tapeInsert floppy tape wafer into next free drive
:nameInsert internal diskette or wafer into next free drive
fileOne or more files to load and execute after auto-boot
.cmd files are run from dos prompt
.cas, .bas and .bds files are loaded into ROM BASIC
Serial Port (RS-232) Options
-r host:portConnect serial port to TCP/IP host, port endpoint.
-r @portListen for TCP/IP connections on port for serial line.
(also -rB for second and -rA for first serial port)
-r :mouseEmulate 2 button mouse on serial port
-r :mouse3Emulate 3 button mouse on serial port
-r :dt1Run DT-1 emulator attached to serial port.
-r :vRun Videotex emulator attached to serial port.
Printer Port Options
-p host:portConnect printer port to TCP/IP host, port endpoint.
-p @portListen for TCP/IP connections on port for printer.
-p :mx70Run MX-70 emulator attached to printer port.
-p :ecRun Electric Crayon emulator attached to printer port.
-poffPrinter appears powered off
View Options
-vaAuthentic display (default)
-vsSharp display
-viSharp display but only allows integer scaling
-vhCheap display
-vNScale cheap or sharp display up by N times
-vfStart in full-screen mode (use Alt+Enter to go windowed)
-vc #RRGGBBSet display colour to 24 bit colour value ("-vc - " for default)
-vd #RRGGBBSet beam conflict colour ("-vd -" for default)
-vb #RRGGBBSet border colour ("-vb -" for default)
-win WxHSet window width and height
-win fullStart in full-screen mode (use Alt+Enter to go windowed)
-bdTurn beam debugging on
-naTurn off authentic display
-wtfs NUpdate window title only every N frames
Sound Options
-muteStart with audio muted.
-vol NSet audio volume percentage (0 to 100; -sv is synonymous)
-suTurn off audio filtering (faster; slightly less accurate)
-sxDisable all audio output
Automation Options
-turboRun at top speed
-batchHave "Record" menu save files without prompting.
-fa hexUpdate FPS when Z-80 hits address
-ta hexTurbo for 5 frames at Z-80 address
-randInitialize RAM and the R register with random data.
Keyboard, Joystick and Light Pen Input
-jxDisable joystick input
-i strSend str as keyboard input (as if it were pasted)
-if fileSend file contents as keyboard input
-iw strWait until str appears on screen
-id NDelay N frames
-itime NGive up on input after N frames of waiting
-ixExit emulator when command line input has been sent
-isSave a screenshot
-icsSave a clean screenshot (no beam interference dropouts)
-itWrite text VRAM to file
-icWrite programmable character generator VRAM to file
-im dump N fileSave ASCII image of disk N to file.
-im wp N on|offEnable or disable write protect on disk N
-im trackdump N file
Save ASCII image of disk track data of disk N to file
-im insert N file
Insert disk image file into drive N
-im eject N 1Eject disk image in drive N with no prompting
-ip host:portRead keyboard input from TCP/IP host, port endpoint.
-ip @portListen for TCP/IP connections on port for keyboard.
-ir audioToggle audio recording (turn on if off, off if on)
-ir flashToggle flash video recording
-ir videoToggle AVI video recording
-ir gifToggle animated GIF recording
-ir mhzToggle MHz recording
-lpEnable light pen emulation (1,3,4)
-esc-exitsPressing the escape key exits trs80gp
Programmer Help
-b hexSet debugger breakpoint (can use "-b hex" up to 4 times).
-b labelSet breakpoint at label (if .bds file loaded)
-b start:endSet breakpoints from start to end (0:ffff can be handy)
-bm hex/labelSet Z-80 memory access breakpoint
also -bmr or -bmw to trap only reads or writes
-bio hex/labelSet Z-80 I/O access breakpoint
also -bior or -biow to trap only reads or writes
-b16 hexSet 68000 debugger breakpoint
-l fileLoad file into memory but don't run it
-ls file.bdsLoad symbols from file but don't load its data.
-eeEnable emulator extensions (debugging oriented)
-traceStart with tracing on (Record → Trace)
-syncTry to maintain frame rate exactly (uses excessive CPU)
-frehdFreHD emulation (time, external file I/O)
Mainly just to demonstrate trsvid
-frehd_dir dirSet directory used for FreHD external file import/export
Also enables FreHD emulation
-trsnicPreliminary trsnic emulation (model 1,3,4 only)
-time render|frame|emulationShow timing in title bar
-showkeyShow Windows key code in title bar
-showframeShow the frame number in title bar
-writeromMake ROM writeable (Model 1 and 3 only)
-m1_vblankVBLANK readable as bit 0 of port $FF (Model I only)
-x1hackTemporary fix for Xenix 1 boot error (and TRSDOS-16)
(disables 68000 to Z-80 interrupt request throuch CTC1)
-mmu9fModel I 16 RAM bank 0 when bit 0 of port $9F set.

Model Selection

The various -m* options and the File → Change Model menu from quite a wide variety of different computers, terminals and printers to emulate. When trs80gp is run from the command line the model will default to -m3. When run from a GUI the model will be whatever was selected by the menu. In either case various preferences like display mode defaults are recalled based on the model.

Many of the command line arguments may not be applicable vary depending on the model. For example, printers and terminals do not have cassette or disk storage and ignore those options. One meaningful difference is the -r0, -r1, -r2, etc. ROM revision. The lower the revision number the earlier the original release of that ROM. Here is a table of revisions for each model which have more that one:

(more info)
-r01.0 - earliest version with a few bugs
-r11.1 - most bugs fixed
-r21.2 - nearly identical to 1.1
-r3yes1.3 - shortened MEM SIZE? prompt; some new features
-r0Early boot rom; no hard-drive boot.
-r1yesChecksum $1BBE with hard-drive boot.
III -r0No shift-down control keys; prints screen if S+P pressed at same time
-r1yesMost common version
4 -r0yesUsual Model 4 ROM
-r1Later "international" ROM; default for -m4ga

Both the Model I and Model III have Level I and Level II BASIC ROMs. The rom revsisions only select between different Level II ROMs. There is only one known version of the Level I ROMs for each.


The Keyboard menu lets you select between Logical Layout (the default) and Physical Layout. There is also Experimental Logical Layout which is (hopefully) temporary. It is identical to Logical Layout except for a slight difference in handling shift key state to work better with a custom CP/M BIOS.

Enable ghosting for a truely authentic experience. Due to the way the keyboard matrix works on the Model 1, 3 and 4 it is possible for a 4th key to appear pressed when 3 others are down. For example, if you press and hold F, G and O in that order you will see FGN on screen as those keys ghost with N.

Logical Layout means that what you see on the key is what gets sent to the TRS-80. This is as you would expect but there are two things to keep in mind. None of the TRS-80 Models sport the full variety of keys on a modern PC. The Model 2 comes closest where the Model 1,3,4 machines lack even square brackets, curly braces and many others. They did, however, have some keys which have no analogue on the PC. Both had a BREAK key for interrupting programs. Models 1,3,4 had CLEAR to clear the screen. The Model 2 had HOLD to pause display. The Model 4 and 4P have a CAPS key for switching between upper and lower-case input.

To GetModel 1,3,4 PressOn Model 2 Press
BREAKEsc, Pause/Break, Endctl-C, Pause/Break, End
CLEARHome, \n/a
CAPSCapsLock, PageUpn/a
HOLDn/actl-shift-@, Scroll Lock
With Physical Layout the emulator is set up so TRS-80 keys are activated by PC keys in roughly the same relative position on the keyboard. Most of the symbols on your keyboard will correspond to the same key on the TRS-80. The letters, numbers, arrow keys and Enter will do what you expect and !#$%;<>,. are in the same spot, otherwise:

To GetPress
`   shift [
@ [
& shift 6
* shift -
( shift 8
) shift 9
- =
+ shift ;
= shift =
: -
' shift 7
" shift 2
Left ], Left
Right \, Right
Up `, Up
Down Tab, Down
Break Backspace, Esc, Pause/Break, End
Clear ', Home
Caps CapsLock, PageUp

Physical Layout is generally only needed for games where a key activated at a different position can make the game unplayable. Note that the Model 2 does not support Physical Layout.

Special Keys

F9 will pause and resume the emulation. You can hold F12 to make the TRS-80 run faster. Pressing shift-F12 will keep it in fast (turbo) mode without having to hold F12. Tapping F12 will put the emulator back to normal speed. The -turbo command line option has the same effect.

In turbo mode keyboard input can get very difficult with characters repeated frequently. trs80gp addresses this by dropping out of turbo mode whenever a key is pressed. This automated return to normal speed can be turned on or off by Keyboard → Auto De-Turbo menu.

Ctrl-Alt-C and Ctrl-Insert and Ctrl-Alt-V and Shift-Insert are shortcuts for "Copy" and "Paste" respectively.

Use F11 to save a screenshot and Shift-F11 to save a cleanshot which is a screenshot without any beam drop-outs that appear as they do on the real Model I.

Alt-F5 activates the machine's reset button. The Model I's reset button is not a hard reset and will not reboot the machine in the case of an especially bad crash. In that case use Ctrl-Alt-F5 to do a warm restart to reboot the emulated Model I or File → Warm Restart. Shift-Ctrl-Alt-F5 or File → Cold Restart is the same as a warm restart but it also re-initializes all RAM.

Alt-Enter will toggle between windowed and full screen mode.

Alt-F4 is the standard Windows shortcut to exit the program which may not be familiar to Wine users. For that matter Alt by itself will move focus to the menu where you can use the keyboard to navigate and Alt-F, Alt-E will active the File, Edit and View menus respectively and so on for other top-level menus.

Soft Keyboard

In unusual circumstances you may need to use the Keyboard → Soft Keyboard... in order to press several keys at once. Most PC keyboards can only show 3 or 4 keys held down at once but some TRS-80 games have easter eggs that require holding down as many as 8 keys. The Soft Keyboard makes this easy as each keyboard button stays pressed when clicked and only releases when clicked again. Or if the corresponding PC key is released.

If nothing else it is laid out the same as the original TRS-80 keyboard so you can see the idea behind Physical Layout mode. And the buttons go up and down as you type. Put the Soft Keyboard window underneath the main one and you'll feel like you're on a real TRS-80. Minutes of fun.

The soft keyboard also has an orange reset button. There's also a "RAM Badge" showing how much memory is installed. Incidentally, the Model 1 and Model 4P didn't have RAM badges and the reset key was in a different location.

Automatic Input

Programs that use the standard ROM or DOS routines for keyboard can have input pushed to them through the Edit → Paste menu entry, "-i" command line flags or Edit → Paste Macro N menu entries. This doesn't work for most games and programs that use their own keyboard input routines. Still, it can be a convenient way to "fast-type" a BASIC program or run a series of TRS-DOS commands. Also note on the Model 2 that trs80gp sends the input to the keyboard hardware and TRS-DOS clears the buffer before reading each command leading to most input being lost (hence the -iw option).

For example, the following command will go into BASIC, set the top of memory to 60000 and then input and run a short BASIC program.

    trs80gp -i "BASIC\r\r60000\r10 ?7*5\rRUN\r"
On the Model 2 we must wait for the "Date" prompt to appear thus making the exercise a bit more complicated:
    trs80gp -m2 -iw Date -i "02/02/1993\r\rBASIC\r10 ?7*5\rRUN\r"
The contents of entire files can be sent using -if filename. Or input can be sent interactively with the Edit → Paste or the Ctrl-Alt-V or Shift-Insert keyboard shortcuts.

Since the characters are fed to keyboard input routines you can enter graphics characters and other data that normally can't be typed in with a real keyboard. Consider this a handy way to put graphics characters inside string literals in BASIC. Normally that requires magic incantations of VARPTR and has been the subject of countless 80 Microcomputer magazine articles.

If the TRS-80 is not calling the standard keyboard input routine then trs80gp will time-out and give up trying to send input after about one minute. Specifically, 3600 frames which is one minute at 60 Hz and one minute and 12 seconds at 50 Hz. Though the emulator automatically switches to turbo mode during automated input so the real time will be less. The timeout value can be changed with the -itime N option.

A few of the options such as -id N (wait N frames) and any which generate screenshots (-is, -ic), exit the emulator (-ix) or write to files (-it, -im) do not wait for keyboard polling and can be used to grab screenshots of games. Though they are of most use in writing the automated tests used by trs80gp's authors. The -showframe option is useful for screenshots as it shows the current emulator frame in the title bar. Thus you needn't guess how many frames to wait before a program is ready for its screenshot.

A facility for entering input to games and other uncooperative programs is being considered.

Paste Macros

The Edit → -> Define Macro... menu allows you to create up to 10 paste shortcuts. The strings entered can be pasted either through the Edit → Paste Macro 0 though 9 menu entires or by pressing Alt-0 though Alt-9. Each macro is automatically saved and there is a different set of macros for each TRS-80 model.

The mechanism is exactly the same as other automatic input so you can use \ escapes to enter control and graphics characters. This is particularly useful for Xenix's virtual console feature where entering \xFC followed by 0 though 9 will switch to that console. For example, to have Alt-4 switch to console 4 set up the macro to send \xFC\x34 or \xFC4 (\x hex escapes consume at most 2 digits).

Light Pen and Joystick

The Windows version supports joystick input on the Model 1, 3 and 4 and light pen input on the Model 1. The light pen must be enabled with the -lp option; the joystick can be disabled with the -jx option.

An Alpha products joystick is emulated using any of the standard joysticks attached to your computer. The actual joystick was a bus hog that would respond to reads on practically any I/O port. Most programs use port $00, $13 or $F7 so only those are mapped by trs80gp.

With the light pen enabled pressing the mouse button down will simulate the light pen making contact with that position on screen. Releasing the mouse button acts as if the pen were removed from the screen. Very few programs were found that have light pen support so please report any problems you see. We'd be very much interested to run some test programs if you have an original light pen.

Working With Floppies

The Diskette menu shows all 4 floppy drives and what disk image is inserted in them or <empty> if there is none. Any disk file name enclosed in << .. >> is a built-in disk image. If the name has an asterisk (*) before it the disk has been modified and must be saved. For non-internal disk images the changes are saved automatically, but changes to internal disk images or disk images loaded from .zip archives must be explicitly saved to another file. trs80gp will remind you to do this if you try to eject a disk with changes or exit the emulator with unsaved changes.

All built-in disk images have a short name that starts with a colon. This is displayed in parenthesis on each entry in the "Insert disk..." menu as a reminder that the short name can be used on the command line to insert the floppy when starting trs80gp.

Each drive has a sub-menu that lets you eject diskettes, replace diskettes, insert diskettes, save them to a new file or toggle their write protection. This isn't the read-only flag of the PC file system but an internal one corresponding to the physical write protect notch on the real floppy disks. Besides saving a copy of a disk image file, Diskette → ... → Export... can write out the disk image in ASCII format or as a track dump in ASCII format for debugging purposes.

The internal diskettes unformatted dmk and unformatted imd are single-sided unformatted diskettes in DMK and IMD format. Equivalent to the -d dmk and -d imd command line options. Your currently running DOS will need to format them before they can be used. unformatted dmk DS and unformatted imd DS are double-sided disk images also accessible from the command line as -d dmk-DS and -d imd-DS.

The -d0, -d1, -d2, -d3, -td and -ld command line options allow you to select disks to insert into the floppy drives when the emulator starts. The default is to put a TRS-DOS floppy in drive :0 so that the TRS-80 will boot into TRS-DOS (which is the same as the -td option). You can just use -d file.dsk to have a floppy disk inserted in the next available drive or just the name of the floppy disk image if it ends in one of the known suffixes (.dmk, .dsk, .imd, .hfe, .jv1 or .jv3.

Whenever a floppy is accessed trsg80p will go into turbo mode automatically. This can be enabled or disabled with the Diskette → Auto Turbo menu. Running in turbo mode has no harmful effect on diskette usage as the necessary relative timing remains the same. Generally you'd only want to turn the feature off to experience the original pace of the machine or when faster disk operations make it hard to read text. Or to keep the TRS-80's real time clock in sync with the current time.

File Import and Export

The built-in utilities floppy provides the IMPORT2 and EXPORT2 to bring files into and out of the emulator. They use the FreHD emulation so trs80gp just be run with the -frehd option for them to work or activated by the Diskette → FreHD menu. Otherwise they will say No FreHD attached and exit. Most Model II operating systems will require the hard drive controller to be disabled (-hx) for the utilities to function.

IMPORT2 will read a file from the host computer and write it to a TRS-80 disk file.

Usage: IMPORT2 [-lnep] hostfile [trs80file]

If the trs80file parameter is omited the last component of the hostfile is used with '.' changed to '/'. If this is not a legal TRS-80 file name you will get an error message.


Convert the host file name to lower case. This is needed for NEWDOS/80 which insists on uppercasing the command line.
Change all newlines ('\n') in the host file to carriage return ('\r')
Most Models: Use the NEWDOS/80 end of file convention. This is required for DOSes such as DOSPLUS which use the NEWDOS/80 convention but are not detected by IMPORT2.
Model II: Write the file with a logical record length of 1. This is required for JCL files and likely most text files.
Model II only - write a program rather than data file. This must be speficied when importing executable (i.e., /CMD files).

EXPORT2 will read a file from the TRS-80 and write it to the host computer.

Usage: EXPORT2 [-lne] trs80file [hostfile]

If the hostfile parameter is omitted the trs80file is used with '/' changed to '.'.


Convert the host file name to lower case. This is needed for NEWDOS/80 which insists on uppercasing the command line.
Change all carriage returns ('\r') in the TRS-80 file to newlines ('\n')
Use the NEWDOS/80 end of file convention. This is required for DOSes such as DOSPLUS which use the NEWDOS/80 convention but are not detected by EXPORT2.

IMPORT2 and EXPORT2 are my modified versions of Frederic Vecoven's modified version of Timothy Mann's originals. VHDUTL is a modified version of Frederic Vecoven's original. My main change was to add support for the Model II operating systems. Note that although there is a utility floppy image for each DOS and model the executables are all identical. The copies are only required because of their incompatible file systems and floppies. The executables themselves detect the DOS they are run under and use the correct system calls.

Except for the Model II they should work on a real machine with a FreHD hard drive emulator. I have not tested this.

For bulk import and export I recommend either creating a /JCL (batch/script file) containing all the commands or using the -i options to have trs80gp do all the typing. There are also command line and GUI utilities to read and write files for many TRS-80 floppy image formats. I recommend the graphical TRSTools utility or the command line trsread & trswrite utilities. Neither have any support for the Model II which was the primary motivation to add IMPORT2 and EXPORT2 to trs80gp.

Internal Floppy Images

A handy table listing all the available internal floppy image files and how they may be accessed from the command line. trs80gp only shows floppies made for the current model in the menu which is generally helpful but you can't use them to boot a Model 4 with a Model III TRSDOS like trs80gp -m4 :td3 will do from the command line. Unless you export the internal :td3 image to a file in Model III mode and then insert that file in Model 4 mode.

Model DOS Menu Entry Type Command Line
I TRSDOS 2.3 << TRSDOS23.DSK >> Boot :td1 or -td
<< m1-trsdos-blank.dmk >> Blank :tb1
<< m1-trsdos-util.dmk >> Utilities :tu1
LDOS 5.3.1 << ld351-1.dsk >> Boot :ld1 or -ld
(also inserts :ld1e)
<< ld351-2.dsk >> Extras :ld1e
<< m1-ldos-blank.dmk >> Blank :lb1
<< m1-ldos-util.dmk >> Utilities :lu1
II TRSDOS 2.0a << TSDOS20A.IMD >> Boot :td2 or -td
<< m2-trsdos-blank.dmk >> Blank :tb2
<< m2-trsdos-util.dmk >> Utilities :tu2
LS-DOS 6.3.1a << l2-631a.dmk >> Boot :ld2 or -ld
<< m2-lsdos-blank.dmk >> Blank :lb2
<< m2-lsdos-util.dmk >> Utilities :lu2
TRSDOS II 4.2 << m2-trsdos4-blank.dmk >> Blank :t4b2
<< m2-trsdos4-util.dmk >> Utilities :t4u2
III TRSDOS 1.3 << TRSDOS13.DSK >> Boot :td3 or -td
<< m3-trsdos-blank.dmk >> Blank :tb3
<< m3-trsdos-util.dmk >> Utilities :tu3
LDOS 5.3.1 << ld3-531.dsk >> Boot :ld3 or -ld
<< m3-ldos-blank.dmk >> Blank :lb3
<< m3-ldos-util.dmk >> Utilities :lu3
4 TRSDOS 6.2.1 << TRS621.DSK >> Boot :td4 or -td
<< m4-trsdos-blank.dmk >> Blank :tb4
<< m4-trsdos-util.dmk >> Utilities :tu4
LS-DOS 6.3.1 << ld4-631.dsk >> Boot :ld4 or -ld
<< m4-lsdos-blank.dmk >> Blank :lb4
<< m4-lsdos-util.dmk >> Utilities :lu4
Any Any << Unformatted dmk >> Unformatted :dmk
<< Unformatted imd >> Unformatted :imd
<< Unformatted dmk DS >> Unformatted :dmk-ds
<< Unformatted imd DS >> Unformatted :imd-ds

Boot Boot floppy for the given DOS. Must go into drive :0
Blank Formatted floppy for the given DOS.
Utility Utility programs for copying files to and from emulated floppies.
Unformatted   Floppy image without any data. Will require a FORMAT before it can be used by a particular DOS.
Extras Second floppy for Model I LDOS which doesn't have the space for everything on a single floppy.

Working With Hard Drives

The Hard Drive menu can attach up to 4 drives. There are only unformatted hard drive images built-in so you will have to either supply your own or go through the process of formatting and otherwise setting up the emulated hard drive for use under your choice of emulated operating system.

Selecting Hard Drive → :slot → << unformatted hdv >> (or "emu" or "DREM") will connect an unformatted hard drive image to the selected controller slot. It will immediately prompt for a file to save the hard drive data. This is unlike the diskettes which will track changes internally and only ask to save when they are ejected.

On the command line use -h :hdv (or :emu or :drem) to attach a blank hard drive image and -hx to disable the hard drive controller.

The "drem" format is compatible with the DREM hard drive emulator available at It stores hard drive images as a pair of files. A file.cfg which gives the geometry and other information and a file.dsk which holds the data for all the blocks.

The "emu" format is compatible with the Gesswein MFM emulator available at Both the "drem" and "emu" formats allow for convenient copying of hard drive images to or from real TRS-80's.

FreHD emulation is not generally compatible with the Model II hard drive. Model II operating systems like the built in TRSDOS-2.0a which are unaware of the hard drive can import and export files using the FreHD utilities. But TRSDOS-II will fail to boot with -frehd enabled.

Working With Cassettes

Cassette tape image files in the standard .cas format can be inserted into the virtual cassette drive with the Cassette → Insert... menu or the -c command line option. Upon insertion trs80gp adds entries to the Cassette menu corresponding to each cassette file found in the .cas image. Normally there is only one file. You can "fast forward" or "rewind" the cassette by selecting the menu entry for a file. Each menu entry gives information on the format of the cassette file, it's name (if any), baud rate and length in seconds.

When the TRS-80 goes to read the cassette (usually as the result of a CLOAD or SYSTEM command) the emulator will send the data to the TRS-80 and go into turbo mode to load the data as quickly as possible. Cassette → Auto Turbo can be used to disable this feature.

When the TRS-80 saves a cassette file (e.g., a CSAVE"A" command is entered) the emulator switches to turbo mode and will prompt you for a PC file in which to save the .cas image. If you'd rather just hear the cassette send to the speaker turn off Cassette → Auto Save.

Working With Aculab Floppy Tapes

The Wafer menu shows all 8 tape drives and what wafer image is inserted in them or <empty> if there is none. Any wafer name enclosed in << .. >> is a built-in wafer image. If the name has an asterisk (*) before it the wafer has been modified and must exported to be saved. For non-internal wafer images the changes are saved automatically. trs80gp will prompt to save modified wafer images when you try to eject them or exit the emulator.

All built-in wafer images have a short name that starts with a colon. This is displayed in parenthesis on each entry in the "Insert wafer..." menu as a reminder that the short name can be used on the command line to insert the wafer when starting trs80gp.

Each drive has a sub-menu that lets you eject, replace, insert, export to a new file or toggle the write protection of a wafer image. This isn't the read-only flag of the PC file system but an internal one corresponding to the physical write protect sticker on real floppy tapes.

You can also use the Wafer menu to manage files on the image. The menu shows a list of files on the wafer. Selecting one will prompt to save it to your PC. A Delete sub-menu also lists the files and selecting an entry will delete that file from the wafer. Finally, the Import... menu lets you copy files from the PC into the wafer image. Because the Aculab firmware may have a copy of a sector in memory is best to @LIST a drive before and after doing any file imports or deletes.

Whenever a wafer is accessed trs80gp will go into turbo mode automatically. This can be enabled or disabled with the Wafer → Auto Turbo menu.

The Wafer → Manual... brings up brief instructions how to activate and use the Aculab Floppy and access the files from within the TRS-80.

Internal Wafer Images

DescriptionCommand Line
5 foot (14 sectors):a5
10 foot (30 sectors):a10
20 foot (64 sectors):a20
30 foot (104 sectors):a30
50 foot (180 sectors):a50
75 foot (252 sectors):a75
Maximum (256 sectors):amax

.tape File Format

Aculab floppy tape wafers are stored in .tape format which is designed to hold not only those images but also Exatron Stringy Floppy images and cassette tapes in various formats. It maintains 99% backwards compatibility by putting an identifying trailer at the end of the file. Simple formats such as .cas will see the trailer as noise at the end of the tape while others will simply ignore it.

The trailer can be up to 255 bytes long and has the following format:

4 bytesMagic string Assist in identifying .tape format.
1 byteTrailer length Currently 9 bytes. Will be longer if .tape format extended.
2 bytesTrailer checksum Computed by setting checksum to 0 and for each trailer byte doing checksum = checksum * 2 + trailer[i]; Stored little-endian and trailer bytes are treated as unsigned.
1 byteFlags bit 0 - write protected if set
bit 1 - has .ESF header
bit 2 - Aculab floppy tape
1 byteData type Character indicating the encoding of the data before the trailer.
'w' - waveform (e.g., audio from cassette)
't' - bit level (i.e., .cas format)
'p' - pulse (.cpt compatible)
'b' - byte stream like bit but without leaders or start bits
'd' - data - high level like sector data or files

trs80gp only creates and understands a specific variant of .tape files for Aculab Floppy Tape emulation — flag bit 2 set, data type 'd' and data consisting of concatenated 256 byte sectors from 0 to the tape size.

When Extratron Stringy Floppy emulation is added to trs80gp it is expected it will be capable of .esf wrapping and bit level encoding.


Output to the cassette, Orchestra 80 or built-in speaker on the Model 4) is played as audio on your PC. Unless the cassette motor is turned on in which case trs80gp will convert that to data (if Cassette → Auto Save is on).

Use File → Mute to toggle sound on and off.

The Printer

Many different types of printers could be attached to a TRS-80. The emulator supports a simple text mode printer. Use Printer → Printer... to see the current output in a "Printer Output" window. There's a Save button to save the output to a file.

The printer window can automatically pop up when the emulator prints something. Use Printer → Auto Popup to enable this feature. You can also simulate a powered-down (or disconnected) printer with Printer → On.

Like the serial ports the printer port can be mapped to a TCP/IP connection. To listen for a connection use -p @port or the "TCP/IP Listen" option in the Printer → Connection... dialog. To make a connection use -p host:port or "TCP/IP Connect" in the connection dialog.

To attach an emulated MX-70 printer use -p :mx70 on the command line or use Printer → Connection... and select it from the drop-down.

The Electric Crayon colour display actually attaches via the printer port. The idea was to make it easy to program. For example, a BASIC LPRINT"ERS" will erase the screen. See the section on the Electric Crayon for some details on how to use it.

In batch mode and TRS-80 printer output is written to a file called trs80-printer.txt.

Serial (RS-232) Ports

trs80gp can map serial ports to TCP/IP connections or emulate 2 and 3 button serial mice. To have a serial port connect to a TCP/IP server use -r host:port or open Serial → Port A, fill in the hostname and port and choose "TCP/IP Connect". Or the serial port can listen on a TCP/IP port with -r @port or use "TCP/IP Listen" in the serial port dialog box. Most machines have a single serial port, the Model 2 line has two ports accessible on the command line with -rA and -rB.

trs80gp instances can now be "wired" together through serial ports. The ultimate setup is one trs80gp running Model 16 Xenix with two trs80gp's attached running DT-1 terminals. But here's a simple example of hooking two DT-1 terminal emulations together.

     trs80gp -mdt1 -r :4000
     trs80gp -mdt1 -r @4000
Characters typed on one of the DT-1's will appear on the second one. Assuming everything is working. If it does not work check the "Status" indicator of each serial port. Both sides should note they are "connected". But the "@" side may only show "Listening..." or the other side "Connecting..." both indicating no connection has been made. Or "-unbound-" if there has been some error.

To break a connection use the "None" option in the dialog box dropdown. The other side may not see the loss of connection so you may need to manually manage "unplugging" on both sides. trs80gp is not quite ready to be an internet "dial-up" BBS.

The status will also show the current transmission settings of the serial port. Baud rate, bits per word, parity and number of stop bits. These do not affect TCP/IP connections but the emulation will limit transmit and receive speeds based on port setup. Most original TRS-80 hardware could be set up to have different transmit and receive speeds. That unlikely configuration will be hidden from view. In the Model 2 line the higher baud rate settings are not exact. trs80gp will display the exact baud rate (feature or bug? You tell me).

As a convenience trs80gp can launch DT-1 and Videotex terminals directly from the command line or in the serial port connection dialog. For example, you might launch a two terminal Xenix system with:

     trs80gp -m6000 -h xenix33.cfg -rA :dt1 -rB :dt1
Or you can choose the desired terminal from the dropdown in the serial port connection dialog. Either way, these terminals will act as a unit with the main trs80gp emulator. If you exit the main emulator the terminals will also be forced to exit.

There is not yet a facility to map serial ports to real serial ports on the host machine.


The screen display and sound of the emulator can be written to a file using the Record → Flash Video and Record → Video menus the start and stop recording. The window title will flash either *flv* or *avi* to remind that that recording is in progress. The "Flash Video" option is recommended as the resulting file size is much smaller than "Video"'s uncompressed .AVI output.

Use Record → Animated GIF to start and stop recording of the screen in animated GIF format. The window title will flash *gif* to let you know GIF recording is in progress. The resulting files are large and not exactly the same frame rate as the TRS-80.

For a screen shot you can use Edit → Copy which copies ASCII text, Unicode and bitmap versions of the screen to the clipboard. Or use the Ctrl-Alt-C and Ctrl-Insert keyboard shortcuts. You can then paste it in Notepad or Paint (or pretty much anything else).

There is also Record → Screenshot to save the screen display as a GIF image (shortcut: F11). Record → Cleanshot or Shift-F11 will save a clean screenshot (or "cleanshot") that does not have the beam drop-outs as normally appeared on the Model I and Model III.

Audio output can be captured in .WAV format using Record → Audio with *wav* flashing in the title bar to let you know it is recording. This is fine for sound effects but unfortunately does not work as a way to create files that can be loaded on real TRS-80's. Instead you should rely on the automatic Cassette → Auto Save feature and use my trld program to convert the .CAS file to .WAV format.

The rest of the Record menu entries are meant for programmers and are documented in the programming section. I will note that Record → MHz Audio records audio files with a very high sampling rate equal to the Z-80 processor speed. Most times you do not need that level of fidelity.

The -batch command line option causes all the Record menu entries to save to a specific file name to allow for fully automated testing of trs80gp itself. It also can be thought of as a way for the emulated TRS-80 to act as a batch processor. More on this in the programming section.

Turbo Mode

trs80gp can be explicitly or manually told to enter turbo mode where the emulated TRS-80 is run faster than real time, sometimes as much as 8 times faster. The entire system and not just the Z-80 is sped up so any virtual I/O between cassette and diskette is not affected nor are any active recordings. It will try to record faster but the resulting recording will be at normal speed. Turn off authentic rendering with View → Authentic Display of the -na command line option to let the TRS-80 run a bit faster.

Use the -turbo command line option to have it run constantly in turbo mode. Or hold the F12 key for a temporary speed boost. shift-F12 will keep turbo mode active without having to hold F12 and will turn off when you release F12.

In order to let you experience the TRS-80 in the best light trs80gp automatically enters turbo mode when doing cassette of diskette I/O. That can be turned off with the Cassette → Auto Turbo and Diskette → Auto Turbo menus.

Normally a turbo mode would cause massive key repeats because your normal typing speed will appear to the TRS-80 as if each key has been held down for a very long time. This is mitigated by trs80gp dropping out of turbo mode whenever a key is pressed. Use Keyboard → Auto De-turbo to turn off this feature if it isn't a problem for your application. Typically games still work fine and you can challenge yourself by playing them at high speed.


By default trs80gp starts in authentic display mode. This mode looks most like the original TRS-80 display and scales very well to fit any window size. It is selected with -va or View → Authentic Display.

For a less realistic but still scalable display there is View → Sharp Display or the -vs flag. In this mode pixels are drawn as tiny rectangles in a single colour rather than the fuzzy dots that are brightest in the middle used in authentic mode.

Since the sharp display doesn't look as good at some scales due to poorer antialiasing there is View → Fixed Sharp Display or -vi. While the window can be resized in this mode the display will only use whole number scales (e.g., 1X, 2X, 3X, etc.) to make the display look as sharp as possible.

Finally there is View → Cheap Display or -vh. It will scale up in whole number jumps it always maintains a correspondence between TRS-80 pixels and PC display pixels even if the aspect ratio is not the same as the original TRS-80 display. The Model I mode is particularly distorted and the window size will change when a Model 4 switches between 80 and 64 character modes. This mode is mainly of benefit to PCs with small displays or less processing power. It is also useful for testing since the mapping from the resulting pixels to TRS-80 graphics is simpler.

While ignored in authentic mode, -vN can be used on the command line to start the emulator at a fixed display scale (e.g., -v3 for 3X scaling). In any mode -win WxH can set the starting window size to W x H.

trs80gp can start in full screen mode (showing no menu bar, window borders or system elements) using -vf or -win full. Use the View → Fullscreen menu entry to switch to full screen mode at any time or toggle between fullscreen and windowed with the Alt-Enter keyboard shortcut. Or use the right-click context menu. Full screen mode is nice for those whose eyesight isn't what it used to be or if you want your PC to feel more like a real TRS-80 instead of an emulation.

The View → Controls dialog allows additional control over the display. There are sliders to adjust the brightness and contrast of the display much like the original TRS-80. It even permits adjustments that leave the display dimmed or brightened beyond readability.

The display colour can be changed from the usual bluish-white to any colour you like with quick presets for Green, Amber and white. Similarly the colour used to show beam conflicts (a programmer feature, more on that below) can also be changed from the default blue. Changes to colours become the default on a per-model basis. I personally like my Model 4 display green and amber for the Model 2. The -vc and -vd command line options can change the display colour without saving it as a default. Or they can specify the factory default by using - as the colour (e.g., -vc -).

Under Windows trs80gp remembers the display mode and window positions for each particular model. The windows can be set up just the way you like them and will be in those positions the next time you run. If you run more than one trs80gp emulator for a model at once the second and subsequent instances will have their own set of window positions and display settings. They will also indicate the instance as a #2, #3, etc. in the window title bar.

Beam Debug

View → Beam Debug (or -bd) turns on beam debug mode which is used to illustrate when the Z-80 and video circuitry conflict over access to display memory. When this happens on a real TRS-80 the video display will show short black streaks (or white in hires) instead of the actual data displayed. This was most prevalent on the Model I and was colloquially referred to as "screen hash" or "snow" or "raster lines". The Model 3 has this to a generally lesser extent. It should appear in Model 4 hires modes and on the Model 2 but, much to my shame, I have not written that emulation yet.

In "Beam Debug" mode these dropouts are instead coloured in blue to made them even more noticeable but yet show what would have been displayed had there been no conflict in shades of blue. This is very helpful for getting the timing right when development programs that write to the display with very precise timing to increase effective display resolution. For instance, see my bouncing ball demo. Beam debug mode reveals how it secretly writes to the display where it is already black so beam conflict remains hidden from view.

This mode also shows the V-Blank and H-Blank portions of the display as rectangular regions below and to the right of the usual display respectively. Z-80 access to video memory during those times will show up as beam conflicts even though there is no actual conflict. Instead they function as a sort of oscilloscope to show when the Z-80 is accessing video memory. H-Blank or "Horizontal Blank" is the short time when the CRT electron beam is moving from the end of a display line to the start of the next one. V-Blank or "Vertical Blank" is a longer interval when the beam is moving from the bottom of the display to the top.

Beam Debug is not supported by the authentic display mode so if activated it will automatically switch the TRS-80 to cheap display mode.


Whether you're writing programs for the TRS-80 or simply wish to dissect existing programs trs80gp has much to offer. As such this section is rather brief on details. Please do get in touch with me if you have questions.

Running Programs

Normally on a TRS-80 programs are run either as /CMD files at the TRS-DOS prompt or loaded from cassette with CLOAD or SYSTEM commands. This is the best way to test programs you write but only needs to be done as a final test. For development trs80gp will directly load programs from the command line or via the File → Run... menu or via drag and drop. This is largely similar to standard procedure but does has its differences. Existing TRS-80 games often work well when run directly but there's no guarantee.

Batch Mode

Activate batch mode using the -batch command line option. In this mode many operations (most in the Record menu) will not prompt for a file name but will instead simple write the file to some fixed file name. This may seem odd but is very useful for testing your programs or trs80gp itself. One way to use this is to have your program write status information to the printer (out $F8 will do on Model 3,4) and use the emulator extensions to make trs80gp exit. You can then run it using:
     trs80gp -m4 -ee program.cmd
And it will go through its paces writing output to trs80-printer.txt. If trs80gp doesn't exit then you know your program went wrong.

In batch mode many of the menu entries switch to saving files without prompting. In most cases those files are named in sequence starting with file-0.txt, file-1.txt and so on. Those are represented by file-%d.txt.

MenuOutput file(s)
Bus Usebus-use-%d.txt
Text VRAMtrs80-text-%d.bin
Character Generator VRAMtrs80-char-%d.bin
Graphics VRAMtrs80-graphics-%d.bin
RAM trs80-ram-%d.bin
RAM16 trs80-ram16-%d.bin
Cassette → Auto Savetrs80-cassette-%d.bin
MHz Audiotrs80-%d-mhz.wav
Z-80 Profileprofile-%d.txt
Flash Videotrs80-%d.flv
Animated GIFtrs80-%d.gif
Diskette (on exit)trs80-drive%d-%d.dsk
Hard Drivetrs80-hard-disk-%d.dsk
Wafer (on exit)trs80-wafer%d-%d.tape

It is worth re-iterating that automated input options are tantamount to scripting control over the emulated TRS-80 and can be used to build up automated tests of your TRS-80 programs.

Z-80 Debugger

The Z-80 debugger may be activated at any time using Debug → Z-80 Debugger... It will also come up automatically when a breakpoint is hit. Breakpoints can be set interactively in the debugger window in the section just below the "Go" button. Breakpoints cover a range of addresses from the value in the left box to the one in the right which will be filled in semi-automatically to specify a single address. Make sure to tick the checkbox next to the start address/label to enable the breakpoint. PC breakpoints can also be set by double-clicking on the Disassembly sub-window.

You may set up to 4 breakpoints of each type. A "PC Breakpoint" is the traditional kind which is triggered whenever a program executes in the given address range. Other types trigger whenever memory is read or written in the range or I/O is performed. These types are useful to find when particular variables are changed or accessed and finding when devices are accessed. Breakpoints may also be set on the command line by the -b, -bm, -bio and related options.

A > appears in the disassembly window to indicate the next instruction to execute and an asterisk (*) to show any active PC breakpoints.

Memory and I/O breakpoints (or if the Z-80 has set breakpoints using the the Emulator Extensions) show extra information in the debug window when they are triggered. The Disassembly sub-window will show a ! to indicate the instruction that caused the fault and additional letter codes indicating what kind of fault or faults occurred. The > will point to the next instruction to execute as usual.

       R      Read protected memory
       W      Write protected memory
       E      Execute protected memory
       S      Stack protected memory
       I      Input protected I/O
       O      Output protected I/O
Various sub-windows show the current Z-80 register contents with them displayed in red if they changed during the previous step. All values are displayed in hexadecimal. There is also a view of the top of the stack and a T-state counter which can be changed as desired to measure intervals interactively.

The Step button moves execution forward a single instruction. Step Over sets a breakpoint after the current instruction and resumes execution. This is useful for CALLs to run quickly though a subroutine. Grizzled Z-80 programmers know there's no guarantee a CALL will return right after itself so caveat emptor. "Go" resumes execution until the next breakpoint or protection violation. The "Emulator Extensions" checkbox may be turned off to disable protection checks.

When single stepping the display will turn gray to give an indication where the CRT beam is at that moment in execution. There are also boxes in the lower left which give the CRT beam raster Y and X coordinates. The debugger is still operational when the TRS-80 is running. You can change registers and memory locations which will show a light-blue background to indicate you've frozen your view of them so you may change it.

Since the screen shows the contents of the previous frame and the drawing of the current frame you will not usually see an immediate change when writing to screen memory. It only shows up when the CRT beam reads and draws it. The debugger memory view gives you the ability to see immediate changes to the various different RAM systems. The defaults is "Z-80 Memory" which shows the Z-80's view of its 65536 memory locations. In the Model 1 and 3 this will show the BASIC ROM in the first 12 or 14 K or memory, the keyboard matrix from $3800 to $3BFF, the video RAM from $3C00 to $3FFF and ordinary RAM from $4000 up to $FFFF or less if a value lower than 48 was given to the -mem command line option. There may be no memory for some of the address space (e.g., $3000 .. $37FF on the Model I). Such regions will display as ~ff (or ~00 on the Model II) and cannot be changed.

You can also select just the RAM to focus on the 48K of memory. But keep in mind these other views use their own addressing. The RAM view starts at 0 but that is seen (by the Model 1 and 3) as starting at $4000. The amount and type of each varies depending on the Model but you'll typically see Text VRAM for the usual character display, and Hires VRAM for the high resolution graphics option (which is usually only accessible to the Z-80 through I/O ports).

You can search through memory by typing a string into the search box. The usual backslash escapes can be used for control and graphics characters: \n, \r, \t and \HH for any hexadecimal value. If the string starts with $ then the rest is taken to be hexadecimal digits with spaces ignored. The < and > buttons cycle through the matches which are highlighted in the memory window below.

In a clunky way RAM can be changed. The easiest approach to to select a memory byte and write a new hexadecimal value for it. The emulator simply reads back the memory dump so you can also delete a line and enter any address followed by a colon and a series of space-separated hexadecimal bytes to change memory locations without having to look at them.

A few pseudo-memory regions are viewable but not changeable. They are intended to give a partial view of the TRS-80 hardware state.

   Z-80 Device        What the Z-80 would return if an I/O were read.
   Z-80 Port Writes   The last value written by the Z-80 to a port.
   Z-80 Port Reads    The last value read from an I/O port by the Z-80.

At the bottom of the window are line of check boxes and drop-downs to control bus tracing which is discussed later.

Most of the Z-80 register state shown is familiar to Z-80 programmers and can be directly altered by Z-80 programs. The IFF1 checkbox is checked when interrupts are enabled (by an EI) instruction and not when they are disabled by a DI instruction or entry into an interrupt routine. Relatedly, IM shows the interrupt mode of the processor which pretty much has to be 1 for Model 1, 3 and 4 computers and 2 for the Model 2 line. The I register is mostly only relevant in interrupt mode 2.

Other state is not directly accessible and pretty much just showing off how accurate trs80gp's Z-80 emulation is.

WZ is an internal temporary register used by Z-80 during various 16 bit operations. In an officially undocumented but reliable quirk of implementation bits 3 and 5 of this register are put into bits 3 and 5 of the flag register F whenever a BIT test is done on (HL)). Early investigators of this called the register MEMPTR. Google "Z80 MEMPTR" or try this link to learn more.

EXX, AFAF', DEHL and DE'HL' show the state of internal flip-flops that select different banks of registers when EXX, EX AF,AF' and EX DE,HL instructions are executed. Effectively they show the number of times modulo 2 each instruction has been executed but the Z-80 program and trs80gp's Z-80 debugger show the currently active sets are you would expect.

The dropdown shows special Z-80 processor states and will spend 99.999% of its time in Normal mode. The other modes are:

Source Level Debugging

My zmac cross assembler will output machine language programs in .bds format. It is a text format so by looking at it and the zmac source code you can probably figure out how to generate it yourself. But the important part here is that loading .bds files from the command line will enable source level debugging.

Use Debug → Source Code to bring up the source code that has been loaded. It will look a bit like an assembler listing file. The current program location will be highlighted and follow the execution of the Z-80.

The format also defines symbolic labels so you can type these labels in to the breakpoint or register windows instead of having to look up the hexadecimal values yourself. You can also use labels for the -b and other command line option to set breakpoints.

In certain situations you may want to have symbols available for a program but don't wish to load it into memory. The -ls command line option and File → Load Symbols... menu entry are used to only load the symbols from a .bds file. Doing so allows you to use symbolic names in the debugger but does not alter RAM contents in case the program is already underway.

Disk Viewer

Under the Debug menu there is a Disk Viewer which allows you to browse through all the floppy and hard drive images inserted and examine their data. There is a search feature to look for strings or binary data. The usual backslash escapes can be used for control and graphics characters: \n, \r, \t and \HH for any hexadecimal value. If the string starts with $ then the rest is taken to be hexadecimal digits with spaces ignored. The < and > buttons will cycle through all the matches.

Use the drop downs to select disk images, sides, tracks and sectors. The sector dropdown presents both the physical and logical sector numbers. The logical number is the value written on the disk and is what is used when we generically refer to reading or writing sector N. The physical number is the relative position of the sector in the track.

Device Map

The debug menu also features the somewhat experimental "Device Map" feature. It gives you a quick overview of the current mappings of Z-80 address and I/O space to RAM and devices. In short, something like the typical memory map seen in programmer guides. Do keep in mind that it shows the mapping when it was brought up. If the program subsequently switches memory maps the window will not be updated.

The feature is experimental mainly because it doesn't yet display all the emulator implicitly knows about the address space. For example, the Model I does not have any memory mapped from $3000 to $36FF but the map will display that as read-only RAM. And it says nothing at all about the memory mapped printer and floppy disk devices accessible in the $3700 - $37FF range. In other words, the map can be incomplete or misleading. But it seems more handy having it around even with its current shortcomings.

Advanced Recording

Sometimes examining memory in the debugger is too cumbersome. The "Text VRAM", "Graphics VRAM" and "RAM" entries in the "Record" menu will save those RAM areas to a file where you can use external tools to do a more thorough analysis.

The normal recording options can assist debugging. It may be helpful to step through a video a frame at a time to see some graphical glitch in detail. The "MHz Audio" option takes this to the extreme by recording audio output a sample rate equal to the speed of the Z-80. In effect this lets you see exactly when the audio changes.

The Trace option is the most useful so I've dedicated section to it. The other options attempt to self-document in their output. Unlike the Trace option these other options don't record everything. Typically they'll just track the PC values to keep overhead low. When they do their final output the use whatever value is in RAM at the time for the disassembly. If the program changes you may seen confusing output. This gets even worse if the memory mapping changes.

All these recording options can be activated and stopped at any time. It is useful and often desirable to start them when the program is stopped in the debugger and then stop them at the next breakpoint after an interesting subroutine or full step of a game simulation has run.

Record → Z-80 Profile tracks every instruction executed and shows you a list of those instructions, the number of times each instruction was executed and the total T-States spent on each instruction. It is intended to help measure where your program spends its time to be used as a guide for optimization. It can also be used to simply track what a program as done during an interval. However, "Bus Use" is better for that task and Trace will show every instruction in order.

Record → Backtrace show the last 65536 instructions executed. In theory you can use this to respond to a crash. But practically speaking that many instructions is at most a tenth of a second so you're not likely to be quick enough to catch it.

Record → Bus Use tracks the execution of a program. The output is much like a disassembler but with markup indicating how memory was accessed: read, written, executed, jumped to, called and so on. The disassembly tends to be better than a static disassembly since it uses the Z-80's execution path to point out what is code and what is data.

The disassembly will be entirely commented out except for any areas where a program was loaded by the command line (or using File → Load/Run) into memory. The intent here is to distinguish the loaded program from the ROM or operating system routines it uses. If the program is sufficiently put through its paces the result should be a good disassembly that can be assembled to produce the original code. Unlike the other trace options any data uncommented in the disassembly is based on the original data loaded so it won't be fooled by simple self-modifying code. However, this is a problem if the program relocates itself. In which case you'll have to get a relocated version of the program loaded. At least "Bus Use" will help understand the relocator code.

Emulator Extensions

These are enabled by the -ee command line option. They can be turned off using the "Emulator Extensions" checkbox in the Z-80 Debugger. A Z-80 program accesses them by sending a function code to I/O port $47. Here is a brief overview:
     0     Set bus permissions for address HL to DE to B
     2     Trigger bus fault B
     3     Disable (B=0) or enable (B=1) bus permissions
     4     Trigger execute fault (i.e., drop into the debugger)
     5     Reset (B=0) or get (B=1, into DEHL) T-state counter
     128   exit emulator with return code BC
     255   set carry flag (to detect if extensions active)
Function 5 allows for automated profiling of Z-80 code. Function 128 is typically used to end a test in batch mode. The bus permissions are very helpful in tracking down nasty bugs. For example, you can set your code section to execute-only. The emulator will trap into the debugger the instant something tries to overwrite over your code. Or even read it. Another useful technique is turning off stack permissions at the bottom and top of your stack to detect stack overflow or underflow.

For function 0 the lower 7 bits in B are set to indicate what Z-80 operation is allowed on that memory location. Or for the first 256 addresses what I/O operation is allowed on a port. Those bits are:

   Mask    Operation  Z-80 Debugger letter indicator
     1     Read       R
     2     Write      W
     4     Execute    E
     8     Stack      S
     16    In         I
     32    Out        O
     64    DMA        D
Stack permission is required for CALL, RET, PUSH, POP, RETI and RETN.

Bus Trace

The Record → Trace feature is a very powerful and comprehensive tool for debugging Z-80 programs and the emulator itself. It can log every instruction executed, memory access, interrupt and I/O port access the Z-80 or any DMA device does. It also places markers in the output file to indicate when a frame has ended and when one second of execution has finished. It can be activated a program start with the -trace option. The full log is recorded in the output file. The last frame or two of the log can be viewed using Debug → Trace Log...

The output can be voluminous. You'll want to use breakpoints to turn tracing on and off for as short a period as possible. The "Tracing" checkpoint in the Z-80 Debugger is a convenient shortcut. And there are additional check boxes to enable or disable tracing for Z-80 instruction, I/O accesses, memory accesses and interrupts.

For even finer control I/O logging can be enabled on a per-device basis. This is handled by the device drop-down. The interface is awkward. As you select each device in the drop-down the checkmark to the right changes to indicate if that device is being logged. But you still must check the I/O box to enable I/O logging. To make it more confusing but usable the best course is to turn I/O off, select the device you're interested in, enable it and then turn I/O back on. If you turn I/O on first it will enable all devices by default.

Yes, it's bad but at least it gives some way to target particular devices. Obviously these controls should be in some other window but the debugger happened to be handy at the time. trs80gp wasn't built in a day.

The actual logging looks something like this:

   8033317 @3018 z ex       jp	$35c2
   8033327 @35c2 z ex       push	af
       +11 @35c2 z wr _ffb4 00 ram[ffb4]
       +11 @35c2 z wr _ffb3 44 ram[ffb3]
   8033338 @35c3 z ex       in	a,($e0)
       +11 @35c3 z in _e0 fb
   8033349 @35c5 z ex       rra
   8033353 @35c6 z ex       jp	nc,$3365
   8033363 @35c9 z ex       rra
   8033367 @35ca z ex       jp	nc,$3369
   8033377 @35cd z ex       push	bc
       +11 @35cd z wr _ffb2 38 ram[ffb2]
       +11 @35cd z wr _ffb1 80 ram[ffb1]
The first column is the T-State counter. The second is the PC of the Z-80 when the operation occurred. Next a letter code shows the device responsible ('z' for Z-80 and 'd' for DMA chip). The type of access follows. Most are "ex" for instruction execution with a disassembly of the instruction following. But for reads, writes, ins and outs (rd, wr, in, ot) the memory or I/O address is shown followed by the value read or written. Other possible operations are:
     ht     Fetch during Z-80 halt
     i0     Interrupt mode 0 bus read
     i1     Interrupt mode 1 bus read
     i2     Interrupt mode 2 bus read
     ni     NMI (non-maskable interrupt) bus read
After any access there may be a description of what the value means to that device and possibly the internal state of the device. A good example is the CRTC video controller chip used in the Model 2 and 4. A I/O write (out) to its address register will be annotated with the name of the register selected. An I/O write will show the name of the register changed and its current value. Some devices are very simple in that any byte read or written can only have one meaning. But for the CRTC a write to a register depends on which register was previously selected. Without the annotation you would have to search backwards for the last register selection. And if the register is 16 bits wide you'd also have to look back for the last time that other 8 bits were changed. This is tedious and may not even appear in the bus trace you've made.

Not all devices provide annotations. If they do then you can bet they were giving us trouble in developing the emulator. Most of the Model 2 devices have annotations.

By the way, the underscore and @ signs in front of addresses are intentional and useful. vi (and maybe other editors) make it easy to search on words. So starting a search on _ffb2 will only find other references to that memory location being read or written. But searching the word ffb2 will find instructions that reference the address. Or you can search for @ffb2 explicitly to restrict your search to only instructions executed at that address.

DT-1 Terminal

The TRS-80 DT-1 (Data Terminal 1) is not a computer but a terminal and as such can do very little without being connected to a computer. It does have a built-in SET-UP screen that needs the DT-1 User's Manual to be understood. Do note that you must press Page-Up on trs80gp to access the setup screen as Ctrl+Shift+Enter will not work. And if you're in the setup screen use Page-Down to active the "KL" easter egg rather than pressing Ctrl+Shift-4.

The trs80gp Setup menu provides all the functionality of the DT-1 SET-UP screen in a somewhat more descriptive format. It will also change the SET-UP screen if you're in it so you can learn the cryptic settings. Use Setup → Duplex → Half to put the DT-1 into a mode where you will see each character you type. If you're feeling really adventurous type <ESC;>G2Blinking<ESC>G0text to see some blinking text.

trs80gp's DT-1 emulation is missing a few features of the original. There's no way to attach a printer, not all input keycodes can be generated, there's no half-intensity text mode and no beep. If you have a real DT-1 please get in touch as a few tests could go along way to implementing the missing features.

TRS-80 Videotex

The TRS-80 Videotex terminal was an early foray into online information access. It had a 300 baud modem allowing it to get the latest news and information. The built-in software is very minimal and trs80gp itself hasn't been polished enough yet to help round off the rough edges.

The Videotex could run in offline mode. It lets you enter pages of text and it was possible to later upload that data to an online service. To experience this, run trs80gp -mv or use File → Change Model → Videotex. Press almost any key (except backspace) and you'll be entering text in the offline mode. Take time to be amazed that it word-wraps text as you type.

If you press backspace (which is a physical mapping of the BREAK key; sorry about that) it will then prompt you with "PLACE CALL". On the real machine you'd pick up your phone, dial the information service. When in answered you'd put the phone down and press ENTER to let it know you're connected.

When you hung up the phone (or the server hung up) the terminal will print OFF LINE indicating this. There was also an LED, I gather. There must be some way to proceed from this point but either I don't know what it is or trs80gp doesn't quite emulate it yet. You can reset the emulator if necessary. You can use another terminal to act as the online service. See the Serial section for general information on how to virtually hook up two trs80gp emulators. Here's a quick rundown of how to see it in action.

  1. Start a Videotex with a DT-1 attached: trs80gp -mv -r :dt1 (or select "DT-1 Data Terminal" from the dropdown in the Serial port dialog box).
  2. Press backspace on the Videotex to see the "PLACE CALL" prompt.
  3. Wait a second or two.
  4. Press Enter on the Videotex.
  5. Typing in the Videotex should now cause characters to appear on the DT-1 side and vice-versa.
  6. Not really a step, but you can use paste on either one as another way to enter text.
  7. Close the DT-1 window and see the Videotex say "OFF LINE".
You may find the Videotex manual and technical documentation helpful. It does support a monochrome 128 x 96 graphics mode. And there was even a way to download 6809 code. At which point the built-in 6809 debugger may see some use.

Electric Crayon

The Electric Crayon is an external device that provides a colour video display. It can work with practically any computer as it connects via the printer port. It was primarily targeted at Model 1 and 3 users as the machines did not have a colour display nor high resolution graphics.

You may attach an emulated Electric Crayon to trs80gp by using -p :ec on the command line or bringing up the Printer → Connection... dialog box and choosing "Electric Crayon" from the dropdown. In either case a new instance of trs80gp will run acting as an Electric Crayon emulator. When launched this way the Electric Crayon emulator will go away when you quit the main trs80gp program.

Even with an Electric Crayon attached trs80gp still records the output to the printer in the normal window. This can be very handy to capture a drawing or debug a program using the Electric Crayon.

You can also just run a standalone Electric Crayon emulation via trs80gp -mec and hook it to another trs80gp emulator using the -p command line options to map TCP/IP connections to the printer port. The Printer section gives some more details on how to do that.

Although the owner had no direct control over the real Electric Crayon, trs80gp supports pasting text to its command processor. Thus even run standalone you can draw using the usual paste methods: Edit → Paste, the input macros or -i on the command line. For example:

       trs80gp -mec -i "A 10 4 HELLO WORLD\r"

Not many programs were written for the Electric Crayon. Here's quick overview of the available commands so you can write some yourself. You can get more detail from the January 1981 issue of 80 Microcomputer. However, don't miss out on the fun of playing with the commands and figuring it out yourself.

A x y string     Display text string.
C n     Select colour.
ERS     Erase display.
H x y len     Draw horizontal line.
M n     Change graphics mode.
I     Invert. (swap between the two palettes)
LD*     Load data or code in S record format.
P n     Set semigraphics value written when drawing.
R x y string     Display string in reversed colours.
S x y     Set pixel (or P pattern if in semigraphics)
V x y len     Draw vertical line.
    Graphics Modes:

    0	alphanumerics and semigraphics-4
    1	2 x 3 semigraphics-6
    2	 64 x  64 x 4 graphics
    3	128 x  64 x 2 graphics
    4	128 x  64 x 4 graphics
    5	128 x  96 x 2 graphics
    6	128 x  96 x 4 graphics
    7	128 x 192 x 2 graphics
    8	128 x 192 x 4 graphics
    9	256 x 192 x 2 graphics

The Electric Crayon's 6800 CPU is fullly emulated. There's a debugger and most of the usual trs80gp programming features.

Linux Notes

Version 2.4 was the first wide release of the Linux version of trs80gp. It has had several releases since there but likely has a small user base. Please get in touch if you run into problems.

Per-user preferences are stored in $XDG_CONFIG_HOME/.config/trs80gp/prefs.ini if the XDG_CONFIG_HOME environment variable is set and not empty. Otherwise $HOME/.config/trs80gp/prefs.ini is used if the HOME environment variable is set. If not, then no preferences will be saved.

MacOS Notes

Some trs80gp features are only available through the command line. The easiest way to run from the command line is use the open command. For example, here is how to start trs80gp in Model I mode with the PCG-80 programmable character graphics generator enabled:
    open --args -m1 -pcg-80
You can run the executable directly which may be preferable in some cases. Just use the path to it inside the directory. Here's how to start a Model II in turbo mode: -m2 -turbo

The End

Pretty much anything else depends on knowing how to operate a TRS-80 or program a Z-80. While it surely would be good to provide links to documentation I'll just leave you with your prior knowledge and good hunting in your web searches.

George Phillips, September 4, 2021. george -at-