xtrs(1) TRS-80 Model I/III/4/4P emulator for the X Window System


xtrs [-model m] [-diskdir d] [-debug] [other options]


xtrs is built on top of a Z-80 emulator, with added routines to support keyboard and video I/O through an X interface. The hardware emulation can operate as a TRS-80 Model I, Model III, Model 4, or Model 4P.

xtrs supports 48K of RAM in Model I or Model III mode, 128K in Model 4 or Model 4P mode. Floppy disks and hard disks are emulated using files to store the data; or under Linux only, real floppy drives can be used. A printer is emulated by sending its output to standard output. A serial port is emulated using a Unix tty device. Cassette I/O is emulated using files to store the cassette data; real cassettes can also be read or written (with luck), either directly through your sound card (on Linux and other systems with OSS-compatible sound drivers), or via .wav files. Game sound and music output are also supported if you have an OSS-compatible sound driver; sound output though the cassette port, through the Model 4 sound option, and through the optional Orchestra-85/90 music synthesizer card are all emulated. In Model I mode, the HRG1B graphics card is emulated. In Model III and 4/4P mode, you can select whether the Radio Shack graphics card or Micro Labs Grafyx Solution is emulated. There is also a mouse driver for Model 4/4P mode. Several common time-of-day clock cards are emulated on all models. The Alpha Products joystick is emulated using the PC's numeric keypad.

Because xtrs emulates the hardware, all known TRS-80 Model I/III/4/4P operating systems should run on it, including all flavors of TRSDOS, LDOS/LS-DOS, NEWDOS, DOSPLUS, MultiDOS, and TRS-80 CP/M. However, the emulator also includes some extensions to the standard hardware, and the special drivers, utilities, and instructions needed for these are not provided for all operating systems.

The Z-80 emulator has a debugger called zbx. You can enter the debugger either by starting xtrs with the -debug flag or by pressing F9 while xtrs is running. The debugger runs in the X terminal window that you started xtrs from. Once you are in the debugger, type "help" for more information.

Special support in the emulator allows the program to block when waiting for information from the keyboard. This will work only for programs that wait for keyboard input using the standard Model I/III ROM call; the emulator decides whether to block the Z-80 program when it tries to read from the keyboard memory by pattern-matching its stack.


The following keys have special meanings to xtrs:

LeftArrow, Backspace, or Delete is the TRS-80 left arrow key. RightArrow or Tab is the right arrow key. UpArrow is the up arrow key. DownArrow or Linefeed is the down arrow key. Esc or Break is the Break key. Home, Clear, or LeftAlt is the Clear key. Control is the Model 4 Ctrl key (address bit 7, data bit 2). RightAlt is equivalent to the shifted down arrow key (used as a control key with some TRS-80 software).

F1, F2, and F3 are the Model 4/4P function keys (address bit 7, data bits 4, 5, and 6). F1 is also the Model I Electric Pencil control key that some users added to their machines. F4 is the Model 4 Caps Lock key (address bit 7, data bit 3). F5, Compose, or ScrollLock is equivalent to the @ key (so that @ can be used as a modifier key). F6 is equivalent to the 0 key (so that a shifted 0 can be obtained). F7 signals a disk change in the emulated floppy drives (see below). F8 exits the program. F9 enters the debugger (zbx). F10 is the reset button.

F11 (or Shift+F1 on some systems) toggles an overlay window which summarizes the above information.

In Model III, 4, and 4P modes, the left and right shift keys are distinct; in Model I mode, they are the same. The PageUp and PageDown keys always activate the positions that correspond to the Model III/4/4P left and right shift keys (address bit 7, data bits 0 and 1 respectively), even in Model I mode. The End key activates an unused position in the keyboard matrix (address bit 7, data bit 7).

The keys [, \, ], ^, _, {, |, }, and ~ also activate unused positions in the keyboard matrix (address bit 3, data bits 3-7). With many TRS-80 keyboard drivers, these keys map to the corresponding ASCII characters; with others, they do nothing. In some cases you may find the shift state is reversed from what it should be; if you press [ but { is displayed instead (etc.), see the -shiftbracket and -noshiftbracket options below to correct the problem. The Insert key maps to the same position as underscore (address bit 3, data bit 7), so that this key can be used both with and without shift pressed; with many TRS-80 keyboard drivers one of these maps to ASCII code 0x7f.

On a German keyboard, the umlaut and "ess-tsett" keys should activate the corresponding characters used in the GENIE, a German Model I clone. This feature is most useful together with the "-charset genie" command line argument.

Pressing a key on a PC numeric keypad with NumLock disengaged emulates the Alpha Products joystick. Keys 2, 4, 6, 8 (KP_Down, KP_Left, KP_Right, KP_Up) are the main directions; keys 1, 3, 7, and 9 (KP_End, KP_Page_Down, KP_Home, KP_Page_Up) work as diagonal directions by activating two main directions at once; and key 0 (KP_Insert) or 5 (KP_Begin) is the fire button. Note that your X server may default to sending digits for the keys on the numeric pad even if NumLock is not pressed. If you have this problem, you can use the xmodmap program to remap your numeric pad, and use the xev program to debug it.

Emulated cassette

To control the emulated cassette, a file called ".cassette.ctl" in the current directory keeps track of what file is currently loaded as the cassette tape and the current position within that file. The cassette(1) shell script provides a way to manipulate this file. You may use this script to load and position cassette tape files. The operation works very much like an actual tape recorder. See the cassette man page for more information about the cassette shell script and the cassette file formats that are supported.


For printer support, any text sent to the TRS-80's printer (using LPRINT or LLIST, for example) is sent to the standard output.

Emulated floppy disks

In Model I mode, xtrs emulates a Radio Shack Expansion Interface with the Percom Doubler or Radio Shack Doubler installed. The Doubler provides double-density disk access by allowing either the stock WD1771 FDC chip or a WD1791 chip to be selected under program control. At powerup the 1771 is selected, so operating systems with no Doubler driver see a stock system. By default, the emulator pretends to be both a Percom and Radio Shack Doubler at the same time -- it responds to the special commands of both -- so a driver for either should work. Under LDOS, use the command "FDUBL" (newer versions of LDOS), or "PDUBL" or "RDUBL" (older versions) to install the driver. Software that tries to detect which doubler you have (such as Super Utility) may be confused by the emulation of both at once, so you can choose to emulate only one with a command line option; see below.

In Model III, 4, or 4P mode, xtrs emulates the stock floppy controller, which uses a WD1793 chip (software-compatible with the WD1791) to provide both single and double density.

Four 5.25-inch floppy drives are emulated, with storage in files named diskM-U, where M is the TRS-80 model (1, 3, 4, or 4p) and U is the drive unit number (0, 1, 2, or 3). If a file of the required name is not found, a drive with no disk in it is emulated (but see below). If the user does not have write permission for a floppy file, and/or the file has an internal write protect flag set, a write-protect tab is emulated. Use the mkdisk(1) program to turn the write protect flag on or off. To change floppies in an emulated drive, rename the existing file for the drive (if any), rename the new floppy file to the proper name, and hit function key F7 in the emulator.

If you try to boot an emulated Model I, III, or 4 with no file named diskM-0 (that is, no disk in drive 0), xtrs emulates having no floppy disk controller. The behavior of a real machine with a disk controller in this case didn't seem useful to emulate faithfully: A real Model I hangs with a screen full of garbage; a real Model III or 4 goes into a retry loop printing "Diskette?" on the screen and rechecking whether you've inserted one. A real Model 4P always has a floppy controller, however, so xtrs always emulates one.

Due to a limitation of the original Model I hardware, drive :3 cannot be double-sided in Model I mode. In the original Model I, you could not have a drive :3 at all if any drive in the system was double-sided, but the emulator is able to be more forgiving.

Emulated floppy image files can be of any of three types: JV1, compatible with Jeff Vavasour's popular freeware Model I emulator for MS-DOS; JV3, a compatible extension of a format first used in Vavasour's commercial Model III/4 emulator; or DMK, compatible with David Keil's Model 4 emulator. All three types work in xtrs regardless of what model it is emulating. A heuristic is used to decide which type of image is in a drive, as none of the types has a magic number or signature.

JV1 supports only single density, single sided, with directory on track 17. Sectors must be 256 bytes long. Use FORMAT (DIR=17) if you want to format JV1 disks with more (or less) than 35 tracks under LDOS.

JV3 is much more flexible, though it still does not support everything the real controllers could do. It is probably best to use JV3 for all the disk images you create, since it is the most widely implemented by other emulators, unless you have a special reason to use one of the others. A JV3 disk can be formatted with 128, 256, 512, or 1024-byte sectors, 1 or 2 sides, single or double density, with either FB (normal) or F8 (deleted) data address mark on any sector. In single density the nonstandard data address marks FA and F9 are also available. You cannot format a sector with an incorrect track number or head number. You can format a sector with an intentional CRC error in the data field. xtrs supports at most 5802 total sectors on a JV3 image.

The original Vavasour JV3 format supported only 256-byte sectors, and had a limit of 2901 total sectors. If you use sector sizes other than 256 bytes or format more than 2901 sectors on a disk image, emulators other than xtrs may be unable to read it. Note that an 80 track, double-sided, double-density (18 sector) 5.25-inch floppy will fit within the original 2901 sector limit; the extension to 5802 is primarily for emulation of 8-inch drives (discussed below).

The DMK format is the most flexible. It supports essentially everything that the original hardware could do, including all "protected" disk formats. However, a few protected disks still may not work with xtrs due to limitations in xtrs's floppy disk controller emulation rather than limitations of the DMK format; see the LIMITATIONS section below.

The program mkdisk(1) makes a blank emulated floppy or "bulk erases" an existing one. By default, mkdisk makes a JV3 floppy, but with the -1 flag it makes a JV1 floppy, or with the -k flag a DMK floppy. See the mkdisk man page for more information.

Early Model I operating systems used an FA data address mark for the directory on single density disks, while later ones wrote F8 but would accept either upon reading. The change was needed because FA is a nonstandard DAM that is fully supported only by the WD1771 floppy disk controller used in the Model I; the controllers in the Model III and 4 cannot distinguish between FA and FB (which is used for non-directory sectors) upon reading, and cannot write FA. To deal nicely with this problem, xtrs implements the following kludge. On writing in single density, an F8 data address mark is recorded as FA. On reading with an emulated WD1771 (available in Model I mode only), FA is returned as FA; on reading with a WD179x, FA is returned as F8. This trick makes the different operating systems perfectly compatible with each other, which is better than on a real Model I! You can use the -truedam flag to turn off this kludge if you need to; in that case the original hardware is emulated exactly.

TRS-80 programs that attempt to measure the rotational speed of their floppy disk drives using timing loops will get the answers they expect, even when xtrs does not emulate instructions at the same speed as the original machines. This works because xtrs keeps a virtual clock (technically, a T-state counter), which measures how much time it should have taken to execute the instruction stream on a real machine, and it ties the emulation of floppy disk index holes to this clock, not to real time.

Emulated 8-inch floppy disks

In addition to the four standard 5.25-inch drives, xtrs also emulates four 8-inch floppy drives. There is no widely-accepted standard hardware interface for 8-inch floppies on the TRS-80, so xtrs emulates a pseudo-hardware interface of its own and provides an LDOS/LS-DOS driver for it.

Storage for the emulated 8-inch disks is in files named diskM-U, where M is the TRS-80 model number (1, 3, 4, or 4p) and U is a unit number (4, 5, 6, or 7). The only difference between 5.25-inch and 8-inch emulated drives is that the emulator allows you to format more bytes per track in the latter. A new JV3 floppy can be formatted as either 5.25-inch or 8-inch depending on whether you initially put it into a 5.25-inch or 8-inch emulated drive. A new DMK floppy, however, must be created with the -8 flag to mkdisk in order to be large enough for use in an 8-inch emulated drive. JV1 floppies cannot be used in 8-inch drives. Be careful not to put an emulated floppy into a 5.25-inch emulated drive after it has been formatted in an 8-inch emulated drive or vice versa; the results are likely to be confusing. Consider using different file extensions for the two types; say, .dsk for 5.25-inch and .8in for 8-inch.

To use the emulated 8-inch drives, you'll need a driver. Under LDOS or LS-DOS, use the program XTRS8/DCT supplied on the emulated floppy utility.dsk. This driver is a very simple wrapper around the native LDOS/LS-DOS floppy driver. Here are detailed instructions.

First, make sure an appropriate version of LDOS is in emulated floppy drive 0, and the supplied file utility.dsk is in another emulated floppy drive. Boot LDOS. If you are using Model I LDOS, be sure FDUBL is running.

Second, type the following commands. Here d is the LDOS drive number you want to use for the 8-inch drive and u is the unit number you chose when naming the file. Most likely you will choose d and u to be equal to reduce confusion.

    Enter unit number ([4]-7): u

You can repeat these steps with different values of d and u to have more than one 8-inch drive. You might want to repeat four times using 4, 5, 6, and 7, or you might want to save some drive numbers for hard drives (see below).

Finally, it's a good idea to give the SYSTEM (SYSGEN) command (Model I/III) or SYSGEN command (Model 4/4P). This command saves the SYSTEM settings, so the 8-inch drives will be available again the next time you reboot or restart the emulator. If you need to access an 8-inch drive after booting from a disk that hasn't been SYSGENed, simply use the same SYSTEM command again.

In case you want to write your own driver for another TRS-80 operating system, here are details on the emulated pseudo-hardware. The 8-inch drives are accessed through the normal floppy disk controller, exactly like 5.25-inch drives. The four 5.25-inch drives have hardware select codes 1, 2, 4, and 8, corresponding respectively to files diskM-0, -1, -2, and -3. The four 8-inch drives have hardware select codes 3, 5, 6, and 7, corresponding respectively to files diskM-4, -5, -6, and -7. (See also the -sizemap option below, however.)

Real floppy disks

Under Linux only, any diskM-U file can be a symbolic link to a real floppy disk drive, typically /dev/fd0 or /dev/fd1. Most PCs should be able to read and write TRS-80 compatible floppies in this way. Many PC floppy controllers cannot handle single density, however, and some may have problems even with double density disks written on a real TRS-80, especially disks formatted by older TRS-80 operating systems. Use the -doublestep flag if you need to read 35-track or 40-track media in an 80-track drive. If you need to write 35-track or 40-track media in an 80-track drive, bulk-erase the media first and format it in the 80-track drive. Don't write to a disk in an 80-track drive if it has ever been written to in a 40-track drive. The narrower head used in an 80-track drive cannot erase the full track width written by the head in a 40-track drive.

If you link one of the 5.25-inch floppy files (diskM-0 through diskM-3) to a real floppy drive, TRS-80 programs will see it as a 5.25-inch drive, but the actual drive can be either 3.5-inch or 5.25-inch. The drive will be operated in double density (or single density), not high density, so be sure to use the appropriate media.

If you link one of the 8-inch floppy files (diskM-4 through diskM-7) to a real floppy drive, TRS-80 programs will see it as an 8-inch drive. Again, you need to use the XTRS8/DCT driver described above to enable LDOS/LS-DOS to access an 8-inch drive. The real drive can be either 3.5-inch, 5.25-inch, or 8-inch. A 3.5-inch or 5.25-inch drive will be operated in high-density mode, using MFM recording if the TRS-80 is trying to do double density, FM recording if the TRS-80 is trying to do single density. In this mode, these drives can hold as much data as a standard 8-inch drive. In fact, a 5.25-inch HD drive holds exactly the same number of bits per track as an 8-inch drive; a 3.5-inch HD drive can hold 20% more, but we waste that space when using one to emulate an 8-inch drive. In both cases we also waste the top three tracks, since an 8-inch drive has only 77 tracks, not 80.

The nonstandard FA and F9 data address marks available in single density on a real Model I with the WD1771 controller also need special handling. A PC-style floppy disk controller can neither read nor write sectors with such DAMs at all. This raises three issues: (1) It will be impossible for you to read some Model I disks on your PC even if your PC otherwise supports single density. In particular, Model I TRSDOS 2.3 directory tracks will be unreadable. (2) On writing in single density, xtrs silently records a F9 or FA DAM as F8. (3) On reading in single density with an emulated WD1771 (Model I mode only), F8 is returned as FA. If you need more accurate behavior, the -truedam flag will turn on error messages on attempts to write F9 or FA DAMs and will turn off translation of F8 to FA on reading.

Hint: Be sure to set the drive type correctly in your PC's BIOS. Linux and xtrs rely on this information to know how fast your drives are spinning and hence what data rate to use when reading and writing. All 3.5-inch drives spin at 300 RPM. Newer 5.25-inch high-density capable drives ("1.2MB" drives) normally always spin at 360 RPM. (Some can be jumpered to slow down to 300 RPM when in double-density mode, but you should not do that when plugging one into a PC.) Older 5.25-inch drives that cannot do high density ("180KB", "360KB" or "720KB" 5.25-inch drives) always spin at 300 RPM. All 8-inch drives spin at 360 RPM. If you plug an 8-inch drive into a PC (this requires a 50-pin to 34-pin adaptor cable), tell your BIOS that it is a 5.25-inch 1.2MB drive.

Emulated hard disks

xtrs can emulate a hard disk in a file in one of two ways: it can use a special, xtrs-specific LDOS driver called XTRSHARD/DCT, or it can emulate the Radio Shack hard drive controller (based on the Western Digital WD1010) and use the native drivers for the original hardware.


The XTRSHARD/DCT driver has been tested and works under both LDOS 5.3.1 for Model I or III and TRSDOS/LS-DOS 6.3.1 for Model 4/4P. It may or may not work under earlier LDOS versions. It definitely will not work under other TRS-80 operating systems or with emulators other than xtrs. The hard disk format was designed by Matthew Reed for his Model I/III and Model 4 emulators; xtrs duplicates the format so that users can exchange hard drive images across the emulators.

To use XTRSHARD/DCT, first run the mkdisk program under Unix to create a blank hard drive (.hdv) file. Typical usage would be: mkdisk -h mydisk.hdv. See the mkdisk(1) man page for other options.

Second, link the file to an appropriate name. XTRSHARD/DCT supports up to eight hard drives, with names of the form hardM-U, where M is the TRS-80 model (1, 3, or 4; in this case Model 4P also uses M=4) and U is a unit number from 0 to 7. It looks for these files in the same directory as the floppy disk files diskM-U.

Third, make sure an appropriate version of LDOS is in emulated floppy drive 0, and the supplied file utility.dsk is in another emulated floppy drive. Boot LDOS. If you are using Model I LDOS 5.3.1, patch a bug in the FORMAT command by typing PATCH FORMAT/CMD.UTILITY M1FORMAT/FIX. You need to apply this patch only once. It must not be applied to Model III or Model 4/4P LDOS.

Fourth, type the following commands. Here d is the LDOS drive number you want to use for the hard drive (a typical choice would be 4) and u is the unit number you chose when naming the file (most likely 0).

    Enter unit number ([0]-7): u
    FORMAT d (DIR=1)

Answer the questions asked by FORMAT as you prefer. The DIR=1 parameter to FORMAT is optional; it causes the hard drive's directory to be on track 1, making the initial size of the image smaller. You can repeat these steps with different values of d and u to have more than one hard drive.

Finally, it's a good idea to give the SYSTEM (SYSGEN) command (Model I/III) or SYSGEN command (Model 4/4P). This command saves the SYSTEM settings, so the drive will be available again the next time you reboot or restart the emulator. If you need to access the hard disk file after booting from a floppy that hasn't been SYSGENed, simply use the same SYSTEM command(s) again, but don't FORMAT. You can freely use a different drive number or (if you renamed the hard disk file) a different unit number.

The F7 key currently doesn't allow XTRSHARD/DCT disk changes to be recognized, but you can change to a different hard disk file for the same unit by renaming files as needed and rebooting LDOS.

Technical note: XTRSHARD/DCT is a small Z-80 program that implements all the required functions of an LDOS disk driver. Instead of talking to a real (or emulated) hard disk controller, however, it uses special support in xtrs that allows Z-80 programs to open, close, read, and write Unix files directly. This support is described further in the "Data import and export" section below.

Using native hard disk drivers

Beginning in version 4.1, xtrs also emulates the Radio Shack hard disk controller (based on the Western Digital WD1010) and will work with the native drivers for this hardware. This emulation uses the same hard drive (.hdv) file format that XTRSHARD/DCT does. With LDOS/LS-DOS, the RSHARDx/DCT and TRSHD/DCT drivers are known to work. With Montezuma CP/M 2.2, the optional Montezuma hard disk drivers are known to work. The hard disk drivers for NEWDOS/80 and for Radio Shack CP/M 3.0 should work, but they have not yet been tested at this writing. Any bugs should be reported.

To get started, run the mkdisk program under Unix to create a blank hard drive (.hdv) file. Typical usage would be: mkdisk -h mydisk.hdv. See the mkdisk(1) man page for other options.

Second, link the file to an appropriate name. The WD1010 emulation supports up to four hard drives, with names of the form hardM-U, where M is the TRS-80 model (1, 3, 4, or 4p) and U is a unit number from 0 to 3. It looks for these files in the same directory as the floppy disk files diskM-U. If no such files are present, xtrs disables the WD1010 emulation.

Note that if hard drive unit 0 is present on a Model 4P (file hard4p-0), the Radio Shack boot ROM will always try to boot from it, even if the operating system does not support booting from a hard drive. If you have this problem, either hold down F2 while booting to force the ROM to boot from floppy, or simply avoid using unit number 0. Stock TRSDOS/LS-DOS 6 systems do not support booting from a hard drive; M.A.D. Software's HBUILD6 add-on to LS-DOS for hard drive booting should work, but is untested. Montezuma CP/M 2.2 does boot from the emulated hard drive.

Finally, obtain the correct driver for the operating system you will be using, read its documentation, configure the driver, and format the drive. Detailed instructions are beyond the scope of this manual page.

Data import and export

Several Z-80 programs for data import and export from various TRS-80 operating systems are included with xtrs on two emulated floppy images. These programs use special support in the emulator to read and write external Unix files, discussed further at the end of this section.

The emulated floppy utility.dsk contains some programs for transferring data between the emulator and ordinary Unix files. IMPORT/CMD, EXPORT/CMD, and SETTIME/CMD run on the emulator under Model I/III TRSDOS, Model I/III LDOS, Model I/III Newdos/80, and Model 4/4P TRSDOS/LS-DOS 6; they may also work under other TRS-80 operating systems. Model III TRSDOS users will have to use TRSDOS's CONVERT command to read utility.dsk.

IMPORT/CMD imports a Unix file and writes it to an emulated disk. Usage: IMPORT [-lne] unixfile [trsfile]. The -n flag converts Unix newlines (\n) to TRS-80 newlines (\r). The -l flag converts the Unix filename to lower case, to compensate for TRS-80 operating systems such as Newdos/80 that convert all command line arguments to upper case. When using the -l flag, you can put a [ or up-arrow in front of a character to keep it in upper case. Give the -e flag if your TRS-80 operating system uses the Newdos/80 convention for representing the ending record number in an open file control block. This should be detected automatically for Newdos/80 itself and for TRSDOS 1.3, but you'll need to give the flag for DOSPLUS and possibly other non-LDOS operating systems. If you need the flag but don't give it (or vice versa), imported files will come out the wrong length. If the destination file is omitted, IMPORT uses the last component of the Unix pathname, but with any "." changed to "/" to match TRS-80 DOS file extension syntax.

EXPORT/CMD reads a file from an emulated disk and exports it to a Unix file. Usage: EXPORT [-lne] trsfile [unixfile]. The -n flag converts TRS-80 newlines (\r) to Unix newlines (\n). The -l flag converts the Unix filename to lower case. When using the -l flag, you can put a [ or up-arrow in front of a character to keep it in upper case. Give the -e flag if your TRS-80 operating system uses the Newdos/80 convention for representing the ending record number in an open file control block. This should be detected automatically for Newdos/80 itself and for TRSDOS 1.3, but you'll need to give the flag for DOSPLUS and possibly other non-LDOS operating systems. If you need the flag but don't give it (or vice versa), exported files will come out the wrong length. If the destination file is omitted, EXPORT uses the TRS-80 filename, but with any "/" changed to "." to match Unix file extension syntax.

SETTIME/CMD reads the date and time from Unix and sets the TRS-80 DOS's date and time accordingly.

The next several programs were written in Misosys C and exist in two versions on utility.dsk. The one whose name ends in "6" runs on Model 4 TRSDOS/LS-DOS 6.x; the other runs on LDOS 5.x and most other Model I/III operating systems.

CD/CMD (or CD6/CMD) changes xtrs's Unix working directory. Usage: CD [-l] unixdir. The -l flag converts the Unix directory name to lower case. When using the -l flag, you can put a [ or up-arrow in front of a character to keep it in upper case. Running CD/CMD will change the interpretation of any relative pathnames given to IMPORT or EXPORT. It will also change the interpretation of disk names at the next disk change, unless you specified an absolute pathname for xtrs's -diskdir parameter.

PWD/CMD (or PWD6/CMD) prints xtrs's Unix working directory.

UNIX/CMD (or UNIX6/CMD) runs a Unix shell command. Usage: UNIX [-l] unix command line. The -l flag converts the Unix command line to lower case. When using the -l flag, you can put a [ or up-arrow in front of a character to keep it in upper case. Standard I/O for the command uses the xtrs program's standard I/O descriptors; it does not go to the TRS-80 screen or come from the TRS-80 keyboard.

MOUNT/CMD (or MOUNT6/CMD) is a convenience program that switches emulated floppy disks in the drives. Usage: MOUNT [-l] filename U. The -l flag converts the Unix filename to lower case. When using the -l flag, you can put a [ or up-arrow in front of a character to keep it in upper case. The filename is any Unix filename; U is a single digit, 0 through 7. The command deletes the file diskM-U (where M is the TRS-80 model) from the disk directory (see -diskdir option), replaces it with a symbolic link to the given filename, and signals a disk change (as if F7 had been pressed).

UMOUNT/CMD (or UMOUNT6/CMD) is a convenience program that removes an emulated floppy disk from a drive. Usage: UMOUNT U. U is a single digit, 0 through 7. The command deletes the file diskM-U (where M is the TRS-80 model) from the disk directory (see -diskdir option) and signals a disk change (as if F7 had been pressed).

The emulated floppy cpmutil.dsk contains import and export programs for Montezuma CP/M, written by Roland Gerlach. It was formatted as a "Montezuma Micro Standard DATA disk (40T, SS, DD, 200K)," with 512-byte sectors. Be careful to configure your CP/M to the proper disk format and drive parameters (40 track, not 80), or you will have confusing problems reading this disk. Documentation is included in the file cpmutil.html and source code in the file cpmutil.tgz (a gzipped tar archive). See http://members.optusnet.com.au/~rgerlach/trs-80/cpmutil.html where you will sometimes find a newer version of the utilities than is included with xtrs.

The emulator implements a set of pseudo-instructions (emulator traps) that give TRS-80 programs access to Unix files. The programs listed above use them. If you would like to write your own such programs, the traps are documented in the file trs_imp_exp.h. Assembler source code for the existing programs is supplied in xtrshard.z, import.z, export.z, and settime.z. You can also write programs that use the traps in Misosys C, using the files xtrsemt.h and xtrsemt.ccc as an interface; a simple example is in settime.ccc.


The emulator supports only interrupt mode 1. It will complain if your program enables interrupts after powerup without executing an IM 1 instruction first. All Model I/III/4/4P software does this, as the built-in peripherals in these machines support only IM 1.

The Model I has a 40 Hz heartbeat clock interrupt, while the Model III uses 30 Hz, and the Model 4/4P can run at either 30 Hz or 60 Hz. The emulator approximates this rather well even on a system where clock ticks come at some frequency that isn't divisible by the emulated frequency (e.g., 100 Hz on Intel Linux), as long as the true frequency is not slower than the emulated frequency. The emulator has a notion of the absolute time at which each tick is supposed to occur, and it asks the host system to wake it up at each of those times. The net result is that some ticks may be late, but there are always the proper number of ticks per second. For example, running in Model I mode on Intel Linux you'd see this pattern: (tick, 30ms, tick, 20ms,...) instead of seeing ticks every 25ms.

Processor speed selection

A standard Model 4 has a software-controlled switch to select operation at either 4.05504 MHz (with heartbeat clock at 60 Hz) or 2.02752 MHz (with heartbeat clock at 30 Hz). xtrs emulates this feature.

Model I's were often modified to operate at higher speeds than the standard 1.77408 MHz. With one common modification, writing a 1 to port 0xFE would double the speed to 3.54816 MHz, while writing a 0 would set the speed back to normal. The heartbeat clock runs at 40 Hz in either case. xtrs emulates this feature as well.


Sound support uses the Open Sound System /dev/dsp device, standard on Linux and available on many other Unix versions as well. This support is compiled in automatically on Linux; if you have OSS on another version of Unix, you'll need to define the symbol HAVE_OSS in your Makefile or in trs_cassette.c. Any time TRS-80 software tries to write non-zero values to the cassette port (or the Model 4/4P optional sound port) with the cassette motor off, it is assumed to be trying to make sounds and xtrs opens /dev/dsp. It automatically closes the device again after a few seconds of silence.

If you are playing a game with sound, you'll want to use the -autodelay flag to slow down instruction emulation to approximately the speed of a real TRS-80. If you don't do this, sound will still play correctly, but the gameplay may be way too fast and get ahead of the sound.

On the other hand, if your machine is a bit too slow, you'll hear gaps and pops in the sound when the TRS-80 program lags behind the demand of the sound card for more samples. The -autodelay feature includes a small speed boost whenever a sound starts to play to try to prevent this, but if the boost is too much or too little, you might either find that the game runs too fast when a lot of sound is playing, or that the sound has gaps in it anyway. If your sound has gaps, you can try reducing the sample rate with the -samplerate flag.

The Orchestra-85 music synthesis software will run under xtrs's Model I emulation, and the Orchestra-90 software will run with Model III operating systems under xtrs's Model III, 4, or 4P emulation. For best results, use Orchestra-90 and the Model 4 emulation, as this lets the software run at the highest emulated clock rate (4 MHz) and thus generate the best sound. If you want to run Orchestra-85 instead, you can tell it that you have a 3.5 MHz clock speedup with enable sequence 3E01D3FE and disable sequence 3E00D3FE; this will let the software run twice as fast as on an unmodified Model I and generate better sound. There is no need to use xtrs's -autodelay flag when running Orchestra-85/90, but you might want to specify a small fixed delay to keep from getting excessive key repeat.


A few Model 4 programs could use a mouse, such as the shareware hi-res drawing program MDRAW-II. The program XTRSMOUS/CMD on the utility disk (utility.dsk) is a mouse driver for Model 4/4P mode that should work with most such programs. xtrs does not emulate the actual mouse hardware (a serial mouse plugged into the Model 4 RS-232 port), so the original mouse drivers will not work under xtrs. Instead, XTRSMOUS accesses the X mouse pointer using an emulator trap. XTRSMOUS implements the same TRSDOS/LS-DOS 6 SVC interface as the David Goben and Matthew Reed mouse drivers. (It does not implement the interface of the older Scott McBurney mouse driver, which may be required by some programs.)

By default XTRSMOUS installs itself in high memory. This is done because MDRAW-II tests for the presence of a mouse by looking to see whether the mouse SVC is vectored to high memory. If the driver is installed in low memory, MDRAW thinks it is not there at all. If you use mouse-aware programs that don't have this bug, or if you edit the first line of MDRAW to remove the test, you can install XTRSMOUS in low memory using the syntax "XTRSMOUS (LOW)".

Time of day clock

Several battery-backed time of day clocks were sold for the various TRS-80 models, including the TimeDate80, TChron1, TRSWatch, and T-Timer. They are essentially all the same hardware, but reside at a few different port ranges. xtrs currently emulates them at port ranges 0x70-0x7C and 0xB0-0xBC. The T-Timer port range at 0xC0-0xCC conflicts with the Radio Shack hard drive controller and is not emulated.

These clocks return only a 2-digit year, and it is unknown what their driver software will do in the year 2000 and beyond. If you have software that works with one of them, please send email to report what happens when it is used with xtrs.

Also see SETTIME/CMD in the "Data import and export" section above for another way to get the correct time into a Z-80 operating system running under xtrs.

Finally, you might notice that LDOS/LS-DOS always magically knows the correct date when you boot it (but not the time). When you first power up the emulated TRS-80, xtrs dumps the date into the places in memory where LDOS and LS-DOS normally save it across reboots, so it looks to the operating system as if you rebooted after setting the date.


Pressing a key on a PC numeric keypad with NumLock disengaged emulates the Alpha Products joystick. See the Keys section above for details. The emulated joystick is mapped only at port 0, to avoid conflicts with other devices. The joystick emulation could be made to work with real joysticks using the X input extension, but this is not implemented yet.

Running games

Some games run rather well under xtrs now, provided that your machine is fast enough to run the emulation in real time and that you choose the right command line options. "Galaxy Invaders Plus" by Big 5 Software is particularly good. You will usually want to turn on autodelay, and if your machine is slow you may need to reduce the sound sample rate. Running your X server in 8-bit/pixel mode also seems to help in some cases. Example command lines:

    startx -- -bpp 8
    xtrs -autodelay

If you have a slow machine and the sound breaks up, it is possible that your machine is not fast enough to generate samples at the default rate of 44,100 Hz. If you think this may be happening, try "-samplerate 11025" or even "-samplerate 8000".


Defaults for all options can be specified using the standard X resource mechanism, and the class name for xtrs is "Xtrs".
-display display
Set your X display to display. The default is to use the DISPLAY environment variable.
Start with the xtrs window iconified.
-background color
-bg color
Specifies the background color of the xtrs window.
-foreground color
-fg color
Specifies the foreground color of the xtrs window.
-title titletext
Use titletext in the window title bar instead of the program name.
-borderwidth width
Put a border of width pixels around the TRS-80 display. The default is 2.
-scale xfac[,yfac]
Multiply the horizontal and vertical window size by xfac and yfac, respectively. Possible values are integers in the range [1,4] for xfac and [1,8] for yfac. Defaults are xfac=1 and yfac=2*xfac.
In Model III or 4/4P mode, resize the X window whenever the emulated display mode changes between 64x16 text (or 512x192 graphics) and 80x24 text (or 640x240 graphics). This is the default in Model III mode, since 80x24 text is not available and the 640x240 graphics add-on card is seldom used.
In Model III or 4/4P mode, always keep the X window large enough for 80x24 text or 640x240 graphics, putting a blank margin around the outside when the emulated display mode is 64x16 text or 512x192 graphics. This is the default in Model 4/4P mode, since otherwise there is an annoying size switch during every reboot.
-charset name
Select among several sets of built-in character bitmaps.

In Model I mode, five sets are available. The default, wider, is a modified Model III set with characters 8 pixels wide; it looks better on a modern computer screen with square pixels than the real Model I fonts, which were 6 pixels wide. lcmod is the character set in the replacement character generator that was supplied with the Radio Shack lower case modification. (It was reconstructed partly from memory and may have some minor bit errors.) stock is the character set in the stock character generator supplied with most upper case only machines. Since xtrs currently always emulates the extra bit of display memory needed to support lower case, this character set gives you the authentic, unpleasant effect that real Model I users saw when they tried to do homebrew lower case modifications without replacing the character generator: lower case letters appear at an inconsistent height, and if you are using the Level II BASIC ROM display driver, upper case letters are replaced by meaningless symbols. early is the same as stock, but with the standard ASCII characters [, \, ], and ^ in the positions where most Model I's had directional arrows. This was the default programming in the Motorola character generator ROM that Radio Shack used, and a few early machines were actually shipped with this ROM. Finally, german or genie gives an approximate emulation of the GENIE, a German Model I clone. Characters are 8 pixels wide, and double width is supported even though later GENIE models did not include it.

In Model III, 4, and 4P modes, three sets are available: katakana (the default for Model III) is the original Model III set with Japanese Katakana characters in the alternate character positions. This set was also used in early Model 4's. international (the default for Model 4 and 4P) is a later Model 4 set with accented Roman letters in the alternate positions. bold is a bold set from a character generator ROM found in one Model III, origin uncertain.

Use X fonts instead of the built-in character bitmaps.
Use the built-in character bitmaps, not a X font. This is the default.
-font fontname
If -usefont is also given, use the specified X font for normal width characters. The default uses a common X fixed-width font: "-misc-fixed-medium-r-normal--20-200-75-75-*-100-iso8859-1".
-widefont fontname
If -usefont is also given, use the specified X font for double width characters. The default uses a common X fixed-width font, scaled to double width: "-misc-fixed-medium-r-normal--20-200-75-75-*-200-iso8859-1".
In Model I mode, emulate the HRG1B 384x192 hi-res graphics card. In Model III mode or Model 4/4P mode, emulate the Radio Shack hi-res card. This is now the default.
In Model III or 4/4P mode, emulate the Micro Labs Grafyx Solution hi-res graphics card. Note that the Model III and Model 4/4P cards from Micro Labs are very different from one another.
Enter zbx, the z80 debugger.
-romfile filename
-romfile3 filename3
-romfile4p filename4p
Use the romfile specified by filename in Model I mode, the romfile specified by filename3 in Model III and Model 4 mode, or the romfile specified by filename4p in Model 4P mode, A romfile can be either a raw binary dump, Intel hex format, or TRS-80 cmd format (for example, a MODELA/III file). If you do not set this option or the corresponding X resource, a default established at compile time is used (if any); see Makefile.local for instructions on compiling in default romfiles or default romfile names.
-model m
Specifies which TRS-80 model to emulate. Values accepted are 1 or I (Model I), 3 or III (Model III), 4 or IV (Model 4), and 4P or IVP (Model 4P). Model I is the default.
-delay d
A crude speed control. After each Z-80 instruction, xtrs busy-waits for d iterations around an empty loop. A really smart C optimizer might delete this loop entirely, so it's possible that this option won't work if you compile xtrs with too high an optimization level. The default delay is 0.
Dynamically adjusts the value of -delay to run instructions at roughly the same rate as a real machine. The tracking is only approximate, but it can be useful for running games.
Turn off -autodelay. This is the default.
-keystretch cycles
Fine-tune the keyboard behavior. To prevent keystrokes from being lost, xtrs "stretches" the intervals between key transitions, so that the Z-80 program has time to see each transition before the next one occurs. Whenever the Z-80 program reads the keyboard matrix and sees an emulated key go up or down, xtrs waits cycles Z-80 clock cycles (T-states) before it allows the program to see another key transition. Key transitions that are received during the waiting period or when the Z-80 program is not reading the keyboard are held in a queue. The default stretch value is 4000 cycles; it should seldom if ever be necessary to change it.
Emulate [, \, ], ^, and _ as shifted keys, and {, |, }, and ~ as unshifted. This is the default in Model 4 and 4P modes, and it works well with the keyboard driver in Model 4 TRSDOS/LS-DOS 6.
Emulate [, \, ], ^, and _ as unshifted keys, and {, |, }, and ~ as shifted. This is the default in Model I and III modes, and it works well with many TRS-80 keyboard drivers. With some keyboard drivers these keys do not work at all, however.
-diskdir dir
Specify the directory containing floppy and hard disk images. If the value starts with "~/" (or is just "~"), it is relative to your home directory. The default value is ".".
-doubler type
Specify what type of double density adaptor to emulate (Model I mode only). The type may be percom, radioshack (or tandy), both, or none. The type may be abbreviated to one character. The default is both, which causes the double density adaptor emulation to respond to the special commands of both the Percom and Radio Shack cards.
Make all real floppy drives double-step, allowing access to 35-track or 40-track media in an 80-track drive. Linux only. See the Floppy Disks section for limitations.
Turn off double-step mode for all real floppy drives. Linux only. This is the default.
-stepmap s0,s1,s2,s3,s4,s5,s6,s7
Selectively set double-step mode for individual real floppy drives. If sU is 2 and diskM-U is a real drive, the drive will be double-stepped; if sU is 1, it will be single-stepped. You can omit values from the end of the list; those drives will get the default value set by -doublestep or -nodoublestep.
-sizemap z0,z1,z2,z3,z4,z5,z6,z7
Selectively set whether drives are emulated as 5-inch or 8-inch; see the section "Emulated 8-inch floppy disks" above. If zU is 5, the drive will appear to Z-80 software as 5-inch; if 8, as 8-inch. The default setting (as reflected in the documentation above) is 5,5,5,5,8,8,8,8. You can omit values from the end of the list; those drives will get the default values. Setting one or more of the first four drives to 8-inch may be useful for CP/M software that supports 8-inch drives. You can also use XTRS8/DCT with 8-inch drives in the first four positions; even though the prompt suggests the unit number must be 4-7, numbers 0-3 are accepted. XTRS8 does not check whether the unit you've selected is really being emulated as an 8-inch drive, however; you'll simply get errors during FORMAT if you get this wrong.
Turn off the single density data address mark remapping kludges described in the "Emulated floppy disks" and "Real floppy disks" sections above. With this option given, the distinction between F8 and FA data address marks is strictly observed on both writing and reading. This option is probably not useful unless you need to deal with Model I disks that use the distinction as part of a copy-protection scheme. See also "Common File Formats for Emulated TRS-80 Floppy Disks", available at http://www.tim-mann.org/trs80/dskspec.html.
The opposite of -truedam. This setting is the default.
-samplerate rate
Set the sample rate for new cassette wav files, direct cassette I/O to the sound card, and game sound output to the sound card. Existing wav files will be read or modified using their original sample rate regardless of this flag. The default is 44,100 Hz. See also the cassette(1) man page.
-serial ttyname
Set the tty device to be used for I/O to the TRS-80's serial port. The default is /dev/ttyS0 on Linux, /dev/tty00 on other versions of Unix. Setting the name to be empty (-serial "") emulates having no serial port.
-switches value
Set the sense switches on the Model I serial port card. This option is meaningful only in Model I mode, and only when the -serial option is not set to "". The default value is 0x6f, which Radio Shack software conventionally interprets as 9600 bps, 8 bits/word, no parity, 1 stop bit.
Disable emulator traps (see "Data import and export") that could write to host files other than disk images in the original diskdir.
The opposite of -emtsafe. This setting is the default.

Additional resources

There are many other TRS-80 resources available on the Web, including shareware and freeware emulators that run under MSDOS and other operating systems, software for converting TRS-80 physical media to the emulator's disk file format, ROM images, and TRS-80 software that has already been converted. For pointers, see http://www.tim-mann.org/trs80.html.

Bugs and limitations

The emulated serial port's modem status and control signals are not tied to the signals on the real serial port, because the real signals are not available to software through the Unix tty device interface. The ability to check for parity, framing, and overrun errors and receive an interrupt when one occurs is not emulated. Unix does not support 2000, 3600, or 7200 baud, so these TRS-80 data rates are remapped to 38400, 57600, and 115200 baud respectively.

A better signal processing algorithm might help read real cassettes more reliably, especially at 1500bps.

Some features of the floppy disk controller are not currently emulated: Force Interrupt with condition bits 0x01, 0x02, or 0x04 is not implemented. Read Track is implemented only for DMK emulated floppies. The multiple-sector flags in Read and Write are not implemented. The timing of returned sectors is emulated only for the Read Address command, and not very accurately for JV1 or JV3. If a disk has more than one sector with the same number on a track, xtrs will always see the first (counting from the index hole) when reading or writing; a real machine would see the next one to come under the head depending on the current rotational position of the disk. Partially reformatting a track (which TRS-80 programs like HyperZap and Model I Super Utility do to achieve mixed density) is supported for DMK but not JV3; however, switching densities while formatting (which Model III and 4 Super Utility do) works on both DMK and JV3.

Real physical floppy disks are supported only under Linux, because Unix does not define a portable interface to the low-level floppy controller functionality that xtrs needs. There are some limitations even under Linux: Index holes are faked, not detected on the real disk, and the timing of returned sectors is not emulated at all. Due to the limitations of PC-style floppy disk controllers, when formatting a physical floppy under xtrs, you cannot mix sectors of different sizes on the same track, switch densities in the middle of a track, or reformat only part of a track. However, xtrs can read and write to physical floppies that have already been formatted in these ways (perhaps by a real TRS-80).

The extended JV3 limit of 5802 sectors is somewhat arbitrary. It could be raised by generalizing the code to permit more than two blocks of 2901, but this does not seem too useful. 5802 sectors is already enough for a 3.5-inch HD (1.44MB) floppy, which the TRS-80 didn't support anyway. If you need more space, use emulated hard drives instead of emulated floppies with huge numbers of tracks.

XTRSHARD/DCT ignores the internal write-protected flag in hard drive images, but a hard drive image can still be effectively write protected by turning off its Unix write permission bits.

The emulator uses a heuristic to decide what format a ROM file is in. If a raw binary ROM image starts with 0x01, 0x05, or 0x22, it can be misidentified as being in a different format. This is rather unlikely to occur, as ROMs typically begin with 0xF3, the DI instruction.

The joystick emulation could be made to work with real joysticks using the X input extension, but this is not implemented yet.

If you discover other bugs, write fixes for any of these, or make any other enhancements, please let us know so that we can incorporate the changes into future releases.

Authors and acknowledgements

xtrs 1.0 was written by David Gingold and Alec Wolman. The current version was revised and much extended by Timothy Mann (see http://tim-mann.org/). See README and README.tpm for additional notes from the authors.

We also thank the following people for their help. The JV1 and JV3 floppy disk file formats were designed by Jeff Vavasour, originally for his MSDOS-based TRS-80 emulators. The DMK format was designed by David Keil for his MSDOS-based TRS-80 emulator. The hard disk file format was designed by Matthew Reed for his MSDOS-based TRS-80 emulators. Al Petrofsky and Todd P. Cromwell III supplied font data. Roland Gerlach contributed the CP/M import and export programs as well as several bug reports and fixes for the emulator itself. Ulrich Mueller added the -borderwidth option, improved the -scale option and the bitmap font scaling, ported the import, export, and settime utilities to Newdos/80, and contributed the HRG1B emulation. Branden Robinson supplied the first version of the cassette man page, fixed Makefile bugs, translated cassette to the Bourne shell, and implemented watchpoints in zbx. Mark McDougall provided documentation for the Micro Labs Grafyx Solution card. Jenz Guenther added the -title option and contributed code to emulate the GENIE (German Model I clone). Joe Peterson contributed code to emulate the TimeDate80 and the -emtsafe feature. Denis Leconte contributed part of the -scale implementation.