Model 600

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First off, just for context and perspective... understand that the Model 600 was frankly a terrible machine, and it was born and died quickly. One estimate is that only 20,000 were ever made. Made, not sold. There is very little 3rd party software, documents, accessories, or knowledge about it.

Pretty much all of what little info and software there is, is contained in the Model 600 directory from the M100SIG archive.


Model 600 Owners Manual
Tandy 600 Handheld BASIC Reference Manual
Developing Applications with Microsoft Works for Model 600
Microsoft Works Utility Disk for Model 600
Service Manual


Copies of the original/full M100SIG, BASIC.!55, and Utility Disk files are here:


Serial cable


Floppy Disks

3.5 inch, DSDD / 2SDD, aka Double Density, aka "720K" floppies

Don't use 1.44M floppies. Or rather, don't depend on them. They won't hurt the drive, and files probably will save and load ok. The problem is just that a DD 720K drive head writes with a much stronger signal that is too strong for the more sensitive magnetic media on a modern HD 1.44M disk. It may seem to work, but it's not reliable as the HD media is being over-driven.

If you have random old unmarked disks, you can identify the correct ones by the square holes in the corners of the disk. 720K disks only have one hole in one corner.

Main Battery

4xD-cell 4.8V, NiCD or NiMH

Select the universal connector. It says "male" in it's description, but it's actually female. The pins are the correct size and spacing and it plugs right onto the 3 pins on the motherboard perfectly, although you have to either release the pins from the connector and reverse the positions of the red and black wires, or just plug the connector onto the motherboard connector off-center, so that the black wire goes to the center pin and the red wire goes to the pin closest to the back of the machine, and an empty position hangs off the side.

Or you can write in the note field during checkout: "3 pin female Molex connector, Pin 1 red, center black, 6" wire" and they will install a keyed connector that you can't plug in backwards.

Be careful how the wire is routed so that the video cable doesn't pull on it when the screen is opened.

This NiMH battery has greater capacity than the original NiCD battery, and can be safely charged by the original NiCD charging circuit, but, there is a NiMH batteries have a shorter self-discharge time than NiCD. The Original NiCD battery had a capacity of only 4,000mah, while this battery has 10,000mah. That means If you charge it today, and then use it all day today, you should get more than twice as many hours of run-time. However, if you charge it today, and then leave it sitting on the shelf, a new NiCD battery might stay more charged for more weeks or months than a new NiMH.

Memory Battery

3.6V NiMH or NiCD

This NiMH battery has greater capacity (80mah) than the original NiCD battery (50mah), and may be safely charged by the NiCD charging circuit. However, it might not be the best choice for a soldered-in memory battery due to NiMH faster self-discharge rate. Modern NiMH are better than older NiMH, so maybe the standard wisdom is no longer necessarily true. Or maybe the greater starting capacity makes the total time to discharge work out about the same. I don't know.


Model 600 comes with 32K of ram built-in, and 1 or 2 96K modules can be added.

Jason Lee-Steere has produced a design for a new 96K memory module you can make yourself.

Option ROMs

The option rom pinout is just plain 27C256 DIP28, so it's simple to copy/modify/create option roms.

There were only 2 option roms ever produced.

The machine shipped with Multiplan by default. Few ever got the BASIC rom, but you mostly don't need it at least today, because there is a disk/ram version of BASIC which you can download, install, and run from ram. It consumes almost 40k of ram, while the option rom version consumes no ram, but then again, today we also have a way to make new ram modules so everyone can max out their machine to 224k, and using the ram version means you don't have to remove your Multiplan rom in order to get BASIC.

So there is no collection of rom images that you can burn to chips and use like Model 100/102 has. But you could replace a missing or damaged rom, or copy your Multiplan or BASIC rom to a new, re-writeable chip to hack on it.

You can read the original roms (all of them, not just the option rom) by just reading them in an eprom programmer as if they were 27C256. And you can make a new rom by just writing to a normal 27C256, and sticking it in a Molex chip carrier. That means it's easy to hack on the system roms.

All you need is:

  • eprom programmer - Suggestion: TL866 (TL866CS or TL866A doesn't matter) There is free software for Windows, Linux, and OSX.
  • One or more 27C256 eprom in DIP28 package. Either one-time-programmable, or UV erasable.
  • If UV erasable, then you also need a UV eprom eraser. The $15 ones on ebay work fine.
  • (optional, recommended) Molex chip carrier
    This is so you don't have to unbend the pins on your multiplan rom to steal it's carrier.
    Molex 50-39-5288 (78802-10)
    EBY 9775-548-28
  • (optional, recommended) Molex socket
    This is again so you don't have to unbend pins on your eprom to re-program it. You can install a 27C256 in a carrier and just leave it. Put the empty Molex socket in *:the ZIF socket in the eprom programmer.
    Molex 15-41-3281 (A78805-0418) or 15-29-9282 (A78805-0518)

I happen to have chanced into a lot of over 130 carriers and sockets for cheap, so if you want one, or a few, just email me, Brian White , and I'll give you a few free, just pay the shipping.

TODO: rom binary format gleaned from the developers manuals and the multiplan rom.
TODO: minipro command lines, esp for forcing a read of the mask roms without chip id.
See dissecting rom directory above


Xmodem Procedure / Installing BASIC

How to get a file from the internet onto the Model 600 using a serial cable.
This example will use BASIC.!55 as the file to transfer.
This is also documented in the Owner's Manual in the TELCOM section.

Get a usb-serial adapter and the special serial cable shown above, or equivalent.

Download files from the Software link above, for instance BASIC.!55 , or anything from the Model 600 directory of the M100SIG archive, to your local modern pc.

On the modern pc, install a serial comm program that has xmodem file transfer. Examples (all free):
Windows: TeraTerm
Linux: minicom
OSX: minicom (macports or brew, or nix)

On the modern machine, start the comm program, select the com port and set the serial settings to 9600 8n1 xon/xoff (aka software flow control).

(The model 600 can be set to 19200, but file transfers don't actually work at that speed.)

On the 600, run TELCOM
Press M [ Modify]
[TAB] to move between fields
name: (leave empty)
baud: 9600
stop: 1
word: 8
xon/xoff: (Yes)
[ENTER] to save and go back to the menu

Press C [Connect]
[TAB] twice
using modem: No

Now it should say ONLINE on the bottom.

Press [Shift]+[Esc] to pull up the telcom menu again without going offline
T [Transfer]
R [Receive]
Protocol: (Xmodem) (you have to press X to select Xmodem)

The Model 600 is now waiting to receive a file.
Now back on the modern machine:
In the comm program, send a file using xmodem, and select BASIC.!55 that you downloaded previously. It takes a few minutes to transfer. Despite the serial port settings being set to 9600baud, the actual speed goes about the same as 600baud. Old forum posts suggest it is slow firmware routines in the Model 600.

When it's done:

On the 600:
D [Disconnect]
Y confirm

Now your should see a new entry, BASIC, in the system manager on the left in the middle.
You now have BASIC installed on your 600!

The maximum single file size you can transfer is 65535 bytes. That is 64K minus one byte.
TELCOM will allow you to transfer up to a full 64K (65536 bytes) before aborting, but if you transfer a full 64K file to the 600, and back, the final byte will be changed from whatever it was to 0x20 (space).

Saving files to disk

This is also documented in the Owner's Manual.

Download the files in the Utility Disk directory, or at the very least FORMAT.!60, to your local PC.

Use the xmodem procedure above to copy all the Utility Disk files, or at least FORMAT.!60 , to the model 600.

Insert a 3.5" DSDD / 2SDD (double density, aka 720K) disk. NOT a 1.44M disk.


Press [CTRL]+[F10] to get back to the system manager.

C [Copy]

COPY file: (arrow down to BASIC, it will show as "BASIC.!55" in this field)


to: A: (you type "A:" in this field)


Now BASIC.!55 has been copied to a disk.
If you wipe the memory on the 600, you can reinstall BASIC by copying from the disk without needing xmodem and a PC any more.

Utility Disk

The model 600 shipped with a floppy disk called Tandy Model 600 Utility Disk
This is just an ordinary disk with the following 5 files on it:


No special boot sectors or anything like that.
To re-create a new Utility Disk, just:

Download all the files from the Utility Disk directory.

Copy each one to the 600 using the xmodem procedure above.

Copy each one to a disk using the copy to disk procedure above.

Then just label the disk, and write-protect it by opening the door in the little square hole in the corner of the disk.

The original disk only had exactly these 5 files on it, but today you might as well put BASIC.!55 on there too.