trs80gp - A TRS-80 Model 1,2,3,4,12,16,6000,Tandy 10,MC-10,Color Computer,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 Tandy 10, TRS-80 Micro Color Computer Model MC-10, TRS-80 Color Computer, TRS-80 DT-1 Data Terminal, TRS-80 Videotex and Electric Crayon external colour display.

The emulator runs on Windows from XP all the way up to Windows 11. 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.

For older versions and checksums, please consult the release notes.

Community

I've 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 Federation 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 of facebook groups dedicated to the TRS-80 models that trs80gp emulates.

Features

• Emulates floppy disk, hard drive, cassette, hires graphics, Orchestra 80/85/90 and printer.
• Window scalable to any size with realistic phosphor-dot rendering.
• Near perfect video emulation including beam drop-outs, wait states and various other subtle effects.
• Can visually indicate Z-80 video memory conflicts.
• Cycle perfect sub-instruction Z-80 and video timing.
• Built-in Z-80 debugger with source level debugging using zmac .bds output.
• 6809 debugger for Videotex and Color Computer
• 6800 debugger for Electric Crayon
• 6803 debugger for MC-10
• 68000 debugger for Model 16 and 6000
• Switchable turbo mode for high speed yet still accurate operation.
• Auto-turbo modes to go fast during slow operations (e.g., disk, cassette) and back to normal when typing.
• AVI and FLV (Flash) video capture.
• GIF and animated GIF screenshot capture.
• Audio capture to WAV file.
• Load programs directly from command line for fast development and testing.
• Can both "paste" and send files as input to keyboard (aka "fast type").
• "Copy" to copy the screen in ASCII, Unicode or graphics format.
• Keyboard selectable between normal and game mode.
• Software keyboard to get around limits of PC keyboards.
• Brightness, contrast and display colour controls.
• Batch mode and command line input to automate tasks.
• Can open files and disk images within .zip archives.
• Optional emulator extensions provide memory protection and timing to the Z-80. And emulator exit.
• Bus tracing, disassembling, profiling, memory dumping and other features for reverse engineering and debugging.

Overview

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:

      trs80gp ball.zip

      trs80gp ball.zip?ball.cas

      trs80gp ball.cas

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 Options
• Model Selection
• The Keyboard
• Light Pen and Joystick
• Floppy Disks
• Hard Drives
• Cassette Tapes
• Aculab Floppy Tapes
• Sound
• Memory
• Endpoints
• Printer
• Serial (RS-232) Ports
• Recording movies, pictures and audio.
• Turbo Mode
• Display
• File Import and Export
• Events
• Programming
• FreHD Emulation
• DT-1 Terminal
• TRS-80 Videotex
• Electric Crayon
• Color Computer
• Tandy 10
• Linux Notes
• MacOS Notes

Command Line Option Summary

Model Selection

See the Color Computer section for how to mix and match combinations of ROM versions.

Keyboard

Enable ghosting for a truly 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. On the Color Computer O, G, N will result in OGF showing up.

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.

Model 2, 12, 16, 6000 and Tandy 10 have a soft capslock option activated with the -ks option or the Keyboard → Soft Capslock. It acts like capslock without using the real capslock key. It can save a lot of trouble switching between the emulator another other applications. It is remembered as a preference and will be activated automatically if you run TRSDOS on the Model 2 or 12 as it requires that all commands use upper case.

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:

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

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.

Software Keyboard

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 software keyboard window underneath the main one and you'll feel like you're on a real TRS-80. Minutes of fun.

The software 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

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"

    trs80gp -m2 -iw Date -iy "%m/%d/%Y\r%h.%i.%s\rBASIC\r10 ?7*5\rRUN\r"

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. Mind you, 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 or disabled entirely with -itime 0.

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. Generally 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.

The -ik will explicitly set individual keys in the keyboard matrix. This can be used to control games and other programs which do not use the standard ROM or DOS keyboard input routines. But you do need to know they keyboard matrix layout and carefully time the input make the whole exercise rather tedious. A better facility for entering input to games and other uncooperative programs is being considered.

The emulator automatically goes into turbo mode when processing input fed in from the command line or pasted directly into it. The speed boost is nice when pasting in BASIC source listing or other large input. It can be turned off with the -iatx on the command line or put on explicitly with -iat. Or use the Edit → Auto Turbo menu entry.

Paste Macros

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). Also, like -iy, "%" substitutions for date and time can be used.

Light Pen and Joystick

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.

For the Color Computer the -js option or Keyboard → Joystick → Swapped will use the second gamepad on your PC as the primary joystick and vice-versa.

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

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.

Unlike actual floppy drives, the emulated drives operate in a special any-sided mode. If a double-sided disk image is inserted, the drive will become double-sided. If the drive has a single-sided disk image and the operating system attempts to format a track on side 2, the drive and disk image will automatically upgrade to double-sided.

To control this behaviour, the The -dNss, -dNds and -dNas command line options allow you to force drive N in the system to behave as single-sided, double-sided or any-sided. Alternatively, you can enable or disable any-sided mode via the Diskette → Drive → Emulate only ... menu option.

Because of problems with CP/M auto-detecting drive sides during FORMAT, the any-sided drive behaviour is not the default on the Model II family. The index hole position is different between single and doubled sided 8" diskettes. Real 8" double-sided disk drives use the position change to actively detect doubled-sided or single-sided diskettes. As a result (unless -dNas is used), the emulator will signal NOT READY from the 8" drive in the follow cases:

• Double-sided image used in a single-sided drive
• Access the second side of single-sided image in a double-sided drive

Note that in this strict mode if you wish to format a double-sided disk image you must insert a double-sided blank as the single-sided blank will not be promoted to double-sided.

Like the original machines, the Model II (-m2) will have single-sided 8" drives and the Models 12, 16, 6000 and Tandy 10 (-m12 -m16 -m6000 -m10) will have double-sided 8" drives.

Internal Floppy Images

File Import and Export

Conversely BASIC programs can be exported by simply listing them to the printer with LLIST and then copying the output seen in the Printer → Printer... window. Or for very short files a File → Copy of what is on the screen will suffice.

The File → Load... menu entry can load a program file into memory. Most of the TRS-80's have either a DUMP or SAVEM command you could use to subsequently save the program to diskette. Debuggers and other system utilities often have similar capabilities. However, you'll need to know where the file loads into memory and the execution address if it is a program file.

For exporting binary data keep the Record -> RAM command in mind. A LOAD PROG/CMD or LOADM can bring a file into memory which can then be extracted from the saved copy of RAM.

Another approach is to use some kind of file transfer program in the emulator that can send or receive files over the RS-232. Since the RS-232 can be hooked to a TCP/IP connection it should be possible to get some kind of utility than can speak xmodem or the kermit protocol or what have you. Or even something of your own devising.

These may not be the most desirable approaches but I mention them as they can be surpisingly handy. Pasting in a basic program from your PC editor and then capturing local edits with LLIST is a fairly decent if somewhat hand-crank development environment. Or sometimes you just need to get something in once to bootstrap a more powerful technique. And some of the tedium can be automated with trs80gp's automatic input facilities.

Model 1,2,3,4,12,16,6000

The built-in utilities floppy has IMPORT2 and EXPORT2 commands to bring files into and out of the emulator. They use the FreHD emulation so trs80gp must be run with the -frehd option for them to work or activated by the Hard Drive → 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 reads a file from the host computer and writes it to a TRS-80 disk file.

Usage: IMPORT2 [-lnepvr] hostfile [trs80file]

If the trs80file parameter is omitted 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.

Options:

-l

Convert the host file name to lower case. This is needed for NEWDOS/80 which insists on uppercasing the command line.

-n

Change all newlines ('\n') in the host file to carriage return ('\r')

-e

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 some other text files.

-p

Model II TRS-DOS only - write a program rather than a data file. This must be speficied when importing executables (i.e., /CMD files).

-v

Model II TRS-DOS only - write input text file as a variable length record file. Lines longer than 255 characters will be split up.

-r

Model II TRS-DOS only - input file is a raw a variable length record file. This is required if the file was originally exported with the -r option.

EXPORT2 reads a file from the TRS-80 and writes it to the host computer.

Usage: EXPORT2 [-lner] trs80file [hostfile]

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

Options:

-l

Convert the host file name to lower case. This is needed for NEWDOS/80 which insists on uppercasing the command line.

-n

Change all carriage returns ('\r') in the TRS-80 file to newlines ('\n')

-e

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.

-r

Model II TRS-DOS only - if the export file has variable length records it will be written in raw variable length record format. This allows guaranteed preservation of variable length record files on export and import. The default translation of them to text files could introduce errors if, for some reason, the file type was not holding a text file.

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.

Variable Length Record Files

Normally they are exported and imported as text files in the standard TRS-80 format with carriage return (character 13) terminated lines. It appears that these variable length record files are primarily used for program source code with each record holding a single line.

When they are exported in raw format each record is preceeded by a length byte which gives the size of the record including the length byte. A length byte of 1 will have no following data. A length of 44 will be followed by 43 bytes of data. A length of 0 is followed by 255 bytes of data.

Model 16, 6000 Xenix Import and Export

There is also the xfile utility. It can read (but not write) Xenix hard drive images. Once trs80gp has been shut down xfile can list or extact files directly from the hard drive image file.

For truly massive file import and export there is a technique where tar archives can be placed into hard drive images. Credit to John Elliott IV for the technique and these instructions on how to do it.

Make a copy of your root filesystem DSK (both the DSK & CFG). Name it something else like scratch.dsk and scratch.cfg. Launch trs80gp, and use the Hard Drive menu to mount the new image on a free drive. On my system, I have HD0 as root and HD1 as /home, so I mount on HD2. On the emulator’s Hard Drive menu, that’s root on :4, home on :5, and ‘scratch’ my extra drive on :6.

Boot XENIX & login. su to root.

To bring files in, on your host system you create a tar file with the items you wish to import. Next, on your host system, you run this command:

	dd if=my-stuff.tar of=/path-to/scratch.DSK obs=512 seek=34

What that does is skip the boot tracks on the HD image and write the tar file to the data portion of the HD image. On your XENIX system, just run tar xvf /dev/hd2. You’ll see the files extracted that you tar’d up on your host system.

To transfer files OUT of the emulator, create a tar file on /tmp or wherever. Next, DD the tar file to /dev/hd2 (in my case, or wherever your ‘scratch’ drive is). So, for example, let’s say I want to get something out of my source directory:

     % su –
     Password:
     # cd /home/iv/src
     # tar cvf /tmp/vim-4.5.tar vim-4.5

     [tar outputs stuff]
     # dd if=/tmp/vim-4.5.tar of=/dev/hd2 obs=512
     iiii blocks in
     oooo blocks out

Next, on your host system, extract your tar file with dd:

    % dd if=scratch.DSK of=/tmp/vim-4.5.tar ibs=512 skip=34 count=oooo

Working With Hard Drives

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 https://www.drem.info/. 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 https://www.pdp8online.com/mfm/mfm.shtml. 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

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. It will prompt you for a PC file in which to save the .cas image when the save is done. If you'd rather just hear the cassette send to the speaker turn off Cassette → Save → Auto.

When auto save is on the emulator waits a fifth of a second after the cassette has stopped before prompting to save the output. In some cases, like when BASIC saves variables to tape, the auto save triggers too quickly. Use the -csd N command line option to increase this delay (given in tenths of a second) or choose one of the presets under the Cassette → Save menu.

When loading a cassette file the emulator displays the cassette counter in the title bar as Cr|123|. When writing the title bar will show Cw|001|. If the counter stops when reading then the emulator has reached the end of the inserted cassette tape image. If the TRS-80 hasn't finished loading then the load has likely failed.

Working With Aculab Floppy Tapes

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

.tape File Format

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

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.

Sound

Use Audio → Mute to toggle sound on and off.

Memory

The standard maximum RAM on a Model 4 was 128 KB. HyperMEM expands that up to a megabyte with -mem hyper:1024 and is represented as a larger RAM in the debugger, recording and trace. For memory sizes greater than 128 K hyperMEM is assumed. -mem 256 is equivalent to -mem hyper:256 on a Model 4.

The Model 4 also features two expansion RAMs, -mem super:1024 and -mem mega:16384. These don't extend main memory but provide a new tranche of banked RAM. The Record menu and the debugger refer to them as "Expansion RAM" and accesses to it show up as expram[] in the trace log.

The Model 4 can have an additional 256K with the XLR8er mod installed via the -z180 flag. The Record menu and the debugger refer to them as "XLR8er RAM" and accesses to it show up as xlr8er_ram[] in the trace log.

Endpoints

Some of these connections would not make physical sense on a real machine. The printer port can be hooked up to the RS-232 serial port. Or the built-in mouse emulation can be tied to the keyaboard input endpoint. trs80gp does not generally limit the possiblities.

Here are all the possible endpoints as they would be written on the command line. When a command line option says it will take an enpoint then any one of these may be written in.

Endpoint	Operation
:port	Connect to the given TCP/IP port on the local host. For example, :8900 to connect to port 8900. trs80gp will keep trying to connect so it will still work if the server is not immediately listening on The port.
@port	Listen for connections on then given TCP/IP port.
host:port	Connect to the given TCP/IP host and port. Like the :port syntax but allows connection to remote machines.
|command %p	trs80gp will listen for TCP/IP connections and put the port number in place of %p in the command line given and run that command. For instance, this will connect a Model 3 to an emulate MX-70 printer: trs80gp -p "|trs80gp -mx70 -p :%p" This is how trs80gp does trs80gp -p :mx70 internally.
/dev/ttyname	Hook device to the Unix hardware serial port (e.g., /dev/ttyUSB0) or named pipe. If hooked to a trs80gp serial port the emulator will control the real serial port baud rate and other communcation parameters.
>filename	Output to the device is written to the given file.
<filename	Input from the device is read from the given file.
<infile>outfile	Combine the <infile and >outfile to specify both where to read input and where to write output.
:loop	Connect a loopback device that will echo any input it receives as output. This will operate like a physical loopback on bidirectional devices like serial ports.
:mouse	Emulated 2 button mouse. Normally only connected to a serial port.
:mouse3	Emulated 3 button mouse. Normally only connected to a serial port.
:dt1	Connect to an emulated DT-1 terminal.
:v	Connect to a Videotex emulator.
:mx70	Connect an emulated MX-70 printer. Normally only attached to printer or serial ports.
:ec	Connect an Electric Crayon Emulator.

Here are the devices that can be hooked up to endpoints, the command line argument for that device hookup and the menu entry that can be used to check the connection status or make a new connection.

Device	Command Line Option	Menu
printer port	-p	Printer → Connection...
serial port	-r or -rA	Serial → Port A...
second serial port	-rB	Serial → Port B...
keyboard input	-ip	Keyboard → Connection...
Becker port	-becker	Serial → Becker...
Events	-event	Debug → Event...

The Printer

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. The printer window is a simple ASCII view of the printer output. It works great for BASIC listings and such but for more complex output see below for how to fully emulate a printer.

As a convenience the emulator goes into turbo mode whenever output is sent to the printer. This "printer auto-turbo" can be turned off and on with the -pt and -ptx command line options or via the Printer → Auto Turbo menu entry.

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 any TRS-80 printer output is written to a file called trs80-printer.txt.

Serial (RS-232) Ports

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

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

On Linux and Mac a serial port can be hooked up to a hardware serial port by specifying the device name. trs80gp cannot do this on Windows as yet. In most cases:

    trs80gp -r /dev/ttyUSB0

Serial port devices cannot be opened by most ordinary (non-root) users by default in linux. There are various ways around this problem but one way is to add yourself to the dialout group with:

    sudo usermod -a -G dialout $USER

Model 1 RS-232 Sense Switches

Recording

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

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.

At the expense of graphical and timing accuracy the emulator can run up to twice as fast as turbo mode with the -haste command line argument (or by using the File → Haste menu item). As the old saying goes, haste makes waste so only use this when speed is vital. Besides only updating the display once per second, "haste" skips wait state calculations which will throw off the timing of a program that accesses the display. Any video capture will also be distorted.

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

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.

FreHD Emulation

Since trs80gp can emulate a hard drive itself, FreHD emulation just means the other handy features of the FreHD such as the real time clock and access to the host file system for file import and export. It also means you can experience TRS-80 video and test your own FreHD files without needing a real TRS-80 or FreHD.

There are only two FreHD features not implemented. The VHDUTL cannot set the clock and you cannot mount floppy disk images through the FreHD using the special DSK/DTC device driver.

In most cases all that's needed is to copy the contents of a FreHD SD card to a directory (or simply mount the SD card on your PC) and run:

     trs80gp -m4 -frehd_dir frehd_file_directory

FreHD setups often come with patched versions of the TRS-80 Model 1, 3 or 4 ROMs that will boot from the FreHD when the machine is powered on. Normally they will only boot from floppy disk and require a special boot floppy that boots with the hard drive active. Add the -frehd_patch option or use Hard Drive → FreHD → ROM Patches to have trs80gp act the same way.

When FreHD emulation is enabled trs80gp will try to connect the image files hard4-0, hard4-1, hard4-2 and hard4-3 in the root of the FreHD directory as hard drives 0 through 3 respectively. But it will only do it when the respective hard drive has no image connected.

The built-in FreHD loader block can be overriden with a custom 256 byte boot block using -frehd_load file.bin or the Hard Drive → FreHD → Loader... menu entry. FreHD's auto-boot normally tries to load the FreHD menu from a frehd.rom file in the FreHD directory. For convenience, trs80gp has a version of the FreHD menu program built-in and you can activate it with -frehd_menu or Hard Drive → FreHD → Built-in Menu.

The FreHD Boot Sequence

The Model 4P is the only TRS-80 in the 1,3,4 line that has hard drive boot code in its ROM. A properly configured hard drive image will boot on the 4P without any FreHD auto-start patches to the 4P's 4K ROM.

The FreHD auto-start patches do not add direct hard-drive booting to the Model 1, 3 or 4. Instead, just before trying to boot off the floppy, they load and execute 256 byte FreHD loader block into RAM location $5000. If the space-bar is held the loader block will return to the ROM and the boot will proceed normally. Otherwise, the loader block will then try to load and execute the frehd.rom menu program from the SD card. Despite it's suffix, the frehd.rom file is actually in /CMD format.

The FreHD menu program displays a nice splash screen which includes the version number of the FreHD firmware (as determined by querying the FreHD itself). It then uses the FreHDs extended facilities to list available hard drive images to boot. When the user selects one it instructs the FreHD to mount that hard drive image and proceeds to boot it.

Booting is mostly a matter of loading the second sector from the hard drive into $4300 (or $4200 on the Model 1) and executing it. Before doing so the FreHD menu will write the current time and date into a few locations. Most TRS-80 operating systems will check for a valid date in these locations when they boot and not prompt for one.

Here is where I am not entirely clear on the exact operation for the FreHD menu program. It will also try to make patches to the boot block and perhaps even the operating system itself. I believe the intent of these patches it to allow certain TRS-80 operating system to accept the pre-initialized time and date. There may well be other purposes.

Boot Sequence in Depth

Note that you could write your own frehd.rom menu program. And in the general sense it could do anything you want. It could just be a game that auto-boots on the FreHD. But if you aim to improve the menu or even make a different loader block then you'll want to consult the source code. And continue reading as I have a few more details on how it all hangs together.

On the Model 3 a fairly short sequence of ROM BASIC commands can be used to mimic the auto-start ROM patch:

     POKE 16912,16
     10 OUT 197,3
     20 IF INP(196)<>254 THEN PRINT"No frehd":END
     30 FORI=0TO255:POKE20480+I,INP(196):NEXT
     RUN
     SYSTEM
     /20480

Notice that the loader block must start with $FE or it will be ignored by the auto-start patch. That's so the auto-start patch has no effect when there is no FreHD attached. It is actually bytes 1 through 255 of loader block that are put into RAM $5000 (20480). The last byte at $50FF is the first byte which is $FE. The initial OUT to port 197 ($C5) serves two purposes. It tells the FreHD to start feeding byte 0 and on of the load block when reads come in on port 196 ($C4). And it outputs that value as byte 2 of the loader block. Since execution begins at byte 1 the loader block must put an instruction there which effectively skips byte 2. As such, loader blocks have byte 1 set to $FE which is the Z-80 CP A,n instruction.

This byte is used by the auto-start patch to indicate to the FreHD menu program what type of TRS-80 it is running on. Hence the 1 for Model 2, 3 for Model 3 and 4 for Model 4. The Model 4P auto-start patch puts in a 5.

If the loader block cannot find a frehd.rom file on the SD card it will simply return and the TRS-80 will boot as normal.

Once the FreHD menu program is loaded it will load the model number from location $5001. Initially it uses the model number to decide if it should use the ROM routine to read the keyboard (1, 2, 3, 4) or its own keyboard scanning for model 5, the 4P. It then scans the root directory of the SD card looking for hard drive image files in HDV format. A file must start with the bytes $56 $CB, have bit 0 of byte 8 set (indicating autoboot) and byte 11, the OS type must be one of:

     0 for LS-DOS 6.3.1
     1 for LDOS 5.3.1
     2 for CP/M
     3 for Newdos 2.5
     4 for Model I LDOS 5.3.1
     5 for Model I NEWDOS 2.5

As mentioned before, once an image is selected it will be mounted as hard drive 0 and the menu will kick off the boot by loading sector 2 from the hard drive into $4300 (or $4200 if the model number is 1).

It will also write the current date and time into one or more memory locations depending on the model number and OS type. This will make most TRS-80 operating systems skip prompting of the date and time as they are already initalized.

Before executing the boot block the FreHD menu system may patch the hard drive boot block (or even, I think, some of the code loaded by the boot block) for unclear purposes. I suspect it is to allow some of the OS's to accept an initialized date. And maybe even patch the OS to load from the hard drive instead of diskette. The menu will also load the modeala.iii from the SD card on the Model 4P if the OS type is 1 or 3 so those Model 3 operating systems will work on a 4P which does not have the necessary BASIC ROM to support them.

After that the FreHD system is out of the picture and the operating systems boots as it would off a regular hard drive.

The diligent programmer can make use of the various memory locations and I/O ports to set breakpoints to inspect the boot process at any point in its various steps. Special FreHD operations such as opening and reading files on the SD card are recognized and displayed clearly in the bus trace allowing a high level view of what a program is doing with the FreHD.

Events

Event messages are send one per line and are simple ASCII text:

dN

Floppy drive N is now active. d-1 means no floppy drive is active.

sN

The active floppy drive has seeked to track N.

hN

Hard drive N is now active. h-1 means no hard drive is active.

eN

The active hard drive has seeked to track N.

c1

The cassette relay has turned on.

c0

The cassette relay has turned off.

p1

Data is being send to the printer.

p0

No data is being send to the printer.

kRCS

The key at row R and column C has been pressed (S=1) or released (S=0). For example, if the A key is tapped on a Model 1 a k011 message will be sent followed closely by a k010. See the keyboard matrices below for how to map row and column numbers to keys for each model.

r1

The reset button has been pressed.

r0

The reset button has been released.

Keyboard Matrices

Model I Keyboard Matrix

Model III Keyboard Matrix

Model 4 Keyboard Matrix

Japanese Model I Keyboard Matrix

Videotex/CoCo matrix

MC-10 Keyboard Matrix

Programming

Running Programs

Batch Mode

     trs80gp -m4 -ee program.cmd

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.

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.

The Z-80 (and other CPUs) 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. A breakpoint can be at a single address or cover a range of addresses using "addr1:addr2" syntax. Make sure to tick the checkbox next to the 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. For Z-80 machines use -b 0 to start the debugger immediately at machine startup or reset. On 6800, 6803 and 6809 machines use -bmr fffe to achieve the same effect.

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 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

The debugger window title will indicate the CPU has stopped, give the memory or I/O address involved and the breakpoint that triggered the stoppage, if any. Programs loaded in .bds form come with memory protection and the debugger will show ".bds file" as the source of a fault. Or "program" if the program itself set up protected memory with emulator extensions.

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 except for the T-state and cycles counters. 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:

• IntrDis - An EI instruction was just executed so the Z-80 will not respond to a maskable interrupt until the next instruction finishes execution.
• Halt - The Z-80 has executed a HALT instruction and will not resume execution until an interrupt occurs. During this time it will continue to fetch and ignore the opcode of the current instruction.
• Pfix, PfIy - The Z-80 is in the middle of a series of $DD and $FD bytes. The Z-80 only pays attention to the last byte in such a series to determine if it has an IX ($DD) or IY ($FD) instruction. The Z-80 cannot be interrupted during this processing but for practical reasons trs80gp breaks such sequences down to a progression of artificial pfix and pfiy instructions.
• PostIff2 - The Z-80 has just executed a LD A,I or LD A,R instruction which will read the wrong value of IFF2 if an interrupt occurs at the same time as the instruction. This is to emulate a Z-80 bug and, unlike the others, does not correspond to a real internal state latch.

The debugger also provides a sub-window for watching expressions. For each expression you choose what result to show: The memory byte or word at the calculated value, or the value itself (or the high/or low byte of the value)

Expressions use C-like syntax consisting of:

• Decimal constants (use $ or 0x to prefix hexadecimal constants)
• Parenthesis to control order of evaluation
• C number operations: + - * / %
• C bit operations: ! ~ << >> & ^ |
• C comparisons: == != < > <= >=
• C logical and/or: && ||
• Register names: e.g. A B C AF HL IX AF'
• Register flags: e.g. F.C, F.N
• Source code symbol values (if loaded)

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.

Some models have built-in symbols and source code which are automatically loaded. While often helpful this sometimes gets in the way of debugging programs. Use the -nrs option or File → Unload Symbols to stop this. Though "Unload Symbols" will drop any other symbols or source code you have loaded.

Disk Viewer

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 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

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

     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
     6     Control recording
              B=$41 - toggle audio recording
              B=$4D - toggle Mhz Audio recording
              B=$47 - toggle animated GIF recording
              B=$46 - toggle Flash video recording
              B=$56 - toggle video recording
              B=$53 - take screenshot
              B=$47 - take cleanshot
   64..127 Set parameter (see below)
     128   exit emulator with return code BC
     255   set carry flag (to detect if extensions active)

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.

Using Emulator Extensions in BASIC

For BASIC where OUT is readily available but setting register contents is difficult there a way to trigger any function with just OUT commands.

OUT 71,32+n will trigger function n using whatever parameters were previously set. A parameter is set by first doing an OUT 71,64+p where p is the parameter number and then doing OUT 71,x to set the value. If a command requires a register then the parameter triggered version of the command will read parameter 2 for register B, parameter 3 for register C, parameter 8 for H and so on. Or put another way, you select the parameter for register R by sending the ascii value of the register letter.

For example, this will toggle animated GIF recording:

    OUT 71,66:OUT 71,71:OUT 71,32+6

INP(71) is used to get results from emulator extensions. Only detection (code 255) and T-state counter read (code 7, B=1) return results. Here is a simple Model III example that checks the emulator extensions are installed. If so, it then reads the number of T-States to execute the little FOR loop and shows them as a raw value and translated to milliseconds.

10 OUT 71,255:IF INP(71)<>1 THEN ?"You forgot -ee":END
20 OUT 71,66:OUT 71,0:OUT 71,37
30 FOR I=1 TO 10:NEXT
40 OUT 71,66:OUT 71,1:OUT 71,37
50 T=0:FOR I=0 TO 3:T=T*256:T=T+INP(71):NEXT
60 ?T;"T states";T/2027.52;"ms"

Bus Trace

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]

     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

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 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

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 escape 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".

Electric Crayon

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.

    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 the usual trs80gp programming features.

Color Computer

Tandy 10

trs80gp's emulation of the Tandy 10 is based on one set of dumped diskettes and an ADOS and BASIC manual. The operation system it runs, ADOS, is a slightly different flavour of CP/M where programs load at hex $1100 rather than $100 and system calls are CALL $1009 instead of CALL 5.

The Tandy 10 has a number of special keys. Many of them are similar in function to modern PCs. Here's how they are mapped:

No examples of PREV PAGE, CURR PAGE, NEXT PAGE, SET ATTR, INS LINE, DEL LINE, FORM SELECT or STATUS LINE being used have been found. The emulator does not know what key codes they generate.

As ADOS is essentially CP/M, menus and error messages use A: and B: to refer to the drives rather than :0 and :1 as is the TRS-DOS family convention.

Input scripting with the -i family of options works but ADOS will tend to abort commands in progress upon any input. Either -iw waits until data is availble or -id frame delays are needed in order to issue multiple commands.

Auto-run of .com or BASIC programs has not been implemented. Nor has FreHD extensions for file import/export.

While the emulation is very functional there are some inaccuracies due to a lack of information:

• Actual boot firmware.
• The exact shape of screen characters.
• The video cursor appearance.
• Exact video timing.
• Speed of blinking.
• Some keys not implemented.
• Serial port (we think it has one).

If you can help with any of these things, please do get in touch.

Linux Notes

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

    open trs80gp.app --args -m1 -pcg-80

    trs80gp.app/Contents/MacOS/trs80gp -m2 -turbo

The End