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.

Most of what little info and software there is, is contained in the Lib-11-TANDY600 directory in the M100SIG archive (backup copy).

See also the venerable Tandy 600 faq. It's a bit out of date, but has been around a long time and is indeed a good run down of most FAQs.


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
Tandy 600 Programmers Reference Guide BIOS and BIOS Specification
File:Tandy Technical Bulletin - Model 600 (1986)(Tandy) Bulletins 001-002.pdf


See the Lib-11-TANDY600 directory in the M100SIG archive

Copies of the Utility Disk files and the RAM and ROM versions of BASIC


Serial cable


Parallel 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, the data will just not be reliable due to the incorrect match between the drive read/write head signal strength and the magnetic media on the disk.

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 inch 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. While you have the machine open, open and close the screen so you can see how the cables get pulled 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.

Many local R/C hobby shops or BatteriesPlus shops will make up a pack like this on demand too. Just show them the old pack and they make a new one just like it easy.

DO NOT leave the wall power plugged in for more than 24 hours! The charging circuit is not "smart" like modern battery charging circuits. It will over-charge and damage the batteries if left plugged in for several days.

You can also simply remove the main battery. The machine runs fine without it. Without the main battery installed, then it would be ok to leave the wall power connected all the time.

Memory Battery

3.6V NiMH or NiCD
3/v80h 2-pin

Current NiMH batteries have greater capacity (80mah) than the original NiCD battery (50mah), and may be safely charged by the NiCD charging circuit.


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

There is a 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.
  • Molex chip carrier
Original carrier manufacturers and part numbers for reference:
Molex 50-39-5288 (78802-10)
EBY 9775-548-28
3D-printed chip carrier:
  • (optional, recommended) Either a Molex 78805 socket, or DIP-28 test clip
This is so you don't have to remove the chip from the carrier to re-program it. Once the chip is installed on a carrier, You can only un-bend the pins once or twice before they break off. Put the empty Molex socket in the ZIF socket in the eprom programmer, or clip the test-clip onto the chip, with ribbon cables to the programer.
Socket part numbers to search for: Molex 15-41-3281 (A78805-0418) or 15-29-9282 (A78805-0518).

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

Alternatively, see Meeprom for a fancier solution to making a re-rwitable option rom that fits in the Molex socket, and does not need an original Molex socket to connect to a programmer, nor a UV eraser.

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


Cold Start

while holding those, press and release POWER.

You must do this on first power-up after the memory battery has been dead or when the memory power switch has been turned off or after installing/removing ram modules.

This wipes all memory.

Warm Start


Resets any running software, but does not wipe memory.

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 (RAM version of BASIC) 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 the RAM version of BASIC, or anything from the Model 600 directory of the M100SIG archive.

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

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 TELCOM app in the 600 allows setting the speed up 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.
(Actually, the drive is single-sided. Single-sided 3.5" disks are rare but they do exist. If you actually have any single-sided 3.5" disks, this (and TPDD1 & TPDD2) is one of the few good uses for them.)


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 from the Software section above.

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.

There is a nice reproduction disk label here: