The later Tandy 1000s from the TL and SL onward came with 101-key keyboards. These keyboards, called the Tandy Enhanced Keyboard, were an autoswitching keyboard that could work in an IBM PC, XT, AT or their clones. This keyboard uses a 5-pin DIN plug and do not work in an earlier Tandy 1000.
In the technical reference manuals for the TL and SL, which are the last Tandy technical reference manuals available online, the keyboard controllers do mention Tandy 1000 Keyboard compatibility. These computers have a 7-pin DIN connector even though an XT or AT keyboard only uses four pins. The schematics indicate that the extra pins are used for Tandy 1000 keyboard-specific signals.
I decided to test my TL to see whether this Tandy 1000 keyboard compatibility was real or just a paper feature. I obtained an 8-pin female DIN connector to plug the Tandy 1000 keyboard into and a 7-pin male DIN connector to plug into the TL.
Here are the pinouts for the Tandy 1000's keyboard :
Tandy 1000 Keyboard
1 - Data
2 - Busy
3 - Ground
4 - Clock
5 - +5v
6 - Reset
7 - NC
8 - NC
And here are the pinouts for the Tandy 1000 TL and SL keyboard's connector :
Tandy TL/SL 7-pin DIN
1 - Clock
2 - Data
3 - NC or Tandy Keyboard Reset
4 - Ground
5 - +5v
6 - NC or Tandy Keyboard Busy
7 - NC Keyboard Type
As you can see, Tandy sought to add signals for the Tandy keyboard around the existing signals for the IBM keyboards. The conversion I came up with is as follows :
TL/SL - 1000
1 - 4
2 - 1
3 - 6
4 - 3
5 - 5
6 - 2
7 - 3
You will note that pins 4 & 7 on the TL/SL end are both wired to pin 3 on the Tandy 1000 keyboard end. This is because TL/SL pin 7 determines the keyboard type. The default is IBM, so you must drive this signal to ground to tell the TL and SL to initialize themselves for the Tandy 1000 keyboard. This wiring does just that. Here is the proper pinout for the male version of a 8-pin DIN connector, and the 7-pin DIN is identical except that it omits the center pin :
It was extremely helpful when soldering the adapter to have a multimeter in a continuity tester mode. This allowed me to ensure that there were no bridged pins and that each wire corresponded to the proper pin. Also, the mirror image numbering between male and female versions of a DIN connector is very confusing, so I look to the back of the female connector as a male connector. It is easier to wire a male connector to a male connector.
When I finished the soldering and tested my pins to ensure they were connected properly, I plugged my Tandy 1000 keyboard into one end and my Tandy 1000 TL into the other end of the adapter. To my amazement, it actually worked! The keyboard LEDs lit up for a moment, which is always a good sign. Even the Hold key did what it was supposed to do. I think I am the first person to ever have attempted this outside Tandy itself!
One thing to note about the SL, the technical reference indicates that U1 must be installed on the keyboard/joystick daughterboard, The only image of the daughterboard I have seen shows that U1 is present, so it probably won't be an issue. This is what it looks like with the proper chips installed :
Although the SL/2 is virtually identical to the SL in terms of hardware, I do not know whether Tandy kept the Tandy 1000 Keyboard compatibility throughout the board revisions of that model. The SL/2 has some differences from the SL, it always uses the updated Bonanza PSSJ chip compared to the SL, early revisions of which used the Jacksboro PSSJ chip. The SL/2 has a later revision of the BIOS 01.04.04, compared to the SL, 01.04.00.
The TL/2 uses a 5-pin DIN, and according to my friend Cloudschatze, the technical notes for that system state that the Tandy 1000 keyboard compatibility was removed. The RL, RL-HD, RLX, RLX-HD. RLX-B, RLX-B-HD, RSX & RSX-HD and TL/3 use PS/2-style 6-pin mini-DIN keyboard and mouse connectors and came later than the TL/2, so they are not compatible either.
So why would anyone want to subject themselves to a Tandy 1000 Keyboard when there are so many better keyboards you can use with a TL or an SL like an IBM Model M or a Northgate Omnikey (no adapters required)? Some Tandy games (King's Quest Tandy booter, Snow Strike) and some Tandy programs (Deskmate through Personal Deskmate 2) refuse to work correctly or will freeze without a Tandy 1000 Keyboard installed. With the Tandy 1000 Keyboard, King's Quest will not refuse to accept further commands if you turn the sound off by pressing the 1 key. Snow Strike becomes playable with a joystick on the Tandy 1000 TL, but pressing a keyboard key in the flight mode will give a momentary pause which will not be present on a Tandy 1000 TX or SX. Without the Tandy 1000 Keyboard, however, Snow Strike would refuse to register any keyboard keypresses after the first one on the TL once you get to trying to fly the airplane.