• Please review our updated Terms and Rules here

AT to XT Keyboard Converter

Or you can just build one yourself on a hunk of perfboard, like I did with the original.

I'm surprised that no one has used the SMT version of the MCU and stuck the whole thing inside of a DIN connector shroud. There's really not much to it--an 8 pin IC and a couple of passives.
 
@ChuckG,

Thanks for the suggestion of building myself, would love to do that. However, I have no way of programming the chip, any suggestions on that?

Also, is this still the latest schematicc (attached picture), is it possible to get a clearer picture?
 

Attachments

  • xtatkey..jpg
    xtatkey..jpg
    15.5 KB · Views: 21
@ChuckG,

Thanks for the suggestion of building myself, would love to do that. However, I have no way of programming the chip, any suggestions on that?

Also, is this still the latest schematicc (attached picture), is it possible to get a clearer picture?

Wow, I'd have to find an 11-year old schematic file? I'll have a look, but no promises.

Most PROM programmers can handle the small PIC chips and there is also the JDM programmer if you've got a real serial port. I think I used PonyProg software to drive it.
 
For what it's worth, here's my schematic in PDF form (done on Eagle). I accessed it last in 2014, so there's been some water under the bridge:
 

Attachments

  • xtatkey.pdf
    12.5 KB · Views: 30
Thanks, I really appreciate you guys digging up the old info, it is very helpful. Of course the challenge is still programming the chip since I don't have any programmer. Will look into the link on building one, though, should be intersting.

Thanks again.
 
Guys,

I found a way to make my Elite/Chicony KB-5181 keyboard work with my Sperry PC/HT.

My keyboard does not have the switch that converts from AT to XT protocol but evidently the version of firmware in my keyboard (controller chip week 29 of 1994) still supports both protocols.

On the circuit board is a place (SW1) for a switch to be mounted (but none actually there) and on the reverse (trace) side there was a blob of solder acting as a jumper, closing the switch and thus keeping it in AT. I desoldered that blob (thus opening the switch) and now it works perfectly as an XT protocol keyboard with the Sperry PC/HT.

Passing this on if it helps anyone out there.

Thanks to all who have responded to my posts!
 
does anybody has a working solution .... HEX for "Zenith Z-150 XT(black label)" keyboard

it has different signals
I found info about it

http://i.imgur.com/q0x8Ayi.png

This is a "normal" XT keystroke with the DATA line held normally low, and CLK normally high. When ready to send a code, 10 CLK falling edges are sent: 2 start bits, 8 data bits, for a total of 10 bits:

http://i.imgur.com/9EaWXlh.png

This is a keystroke from the Z-150. The DATA line is held normally high (opposite). When ready to send a code, only 9 CLK falling edges are sent for a total of 9 bits. I'm guessing there is only 1 start bit.
the text is taken from here , also there a pictures from logic analyzer"

https://deskthority.net/viewtopic.php?f=2&t=12972&start=30#p354189
 
Hi,

at first, sorry for my english :rolleyes: and a big thanks to Chuck(G)! I read this thread with enthusiasm and built one of those nice converters for a special terminal. Because the logic of shift-register differs a little bit, I had to make some changes, stumbled about little mistakes and had ideas of improvement, especially got some more PS/2-keyboards working.

I think it's fair to share the code again:
http://pontacko.tfn-clan.de/files/at2xt/XTATKEY_RT01.ZIP

So everyone with problems can give this a try or transfer ideas.

regards

So i have burned the XTATKey RT01 and the .094 version of the firmware to different PIC12F629's. the .094 the caps lock, num lock and scroll lock LED's turn on and off depending on the state of the keyboard. Great. But the buffer is off when if I type while a program is loading it misses characters.

The RT01 firmware works with the buffer but does not appear to control the LEDs for CAPS lock, Scroll lock and Num Lock. Is there an updated version of the RT01 that does that?
 
The funny thing about the converter is that I didn't need one at the time--I still have XT-compatible keyboards. But I wanted a challenge to see how cheaply one could be constructed. At the time, the PIC12F629 was about the cheapest MCU capable of doing the work. I was considering the 6-pin PIC10F MCUs, but not enough I/O pins.

Of course, nowadays, the picture has changed--silicon has gotten stupid-cheap and even light bulbs have MCUs in them, not to mention pet toys and Christmas lights. My last keyboard-oriented project (done a couple of years ago) was to convert an IBM iPoint IR keyboard to a PS/2 interface. For that, I used a STM32F103 "blue pill"--way overkill for the job, but still stupid cheap. It could easily be adapted to be USB interface as well, but I have no use for such a gizmo.

I wonder if one of those sub-$0.10 Chinese OTP MCUs could be used for the ATXT keyboard converter... ;)
 
The RT01 firmware works with the buffer but does not appear to control the LEDs for CAPS lock, Scroll lock and Num Lock.
I put Schnurzels RT01 code into the PIC12F629 of an AT2XTKB connected to my IBM XT. I then used that AT2XTKB with the IBM 84-key keyboard supplied with early IBM AT's, and with a Honeywell keyboard. On both keyboards, the NUM LOCK, CAPS LOCK, SCROLL LOCK lights behaved as expected (e.g. each press of the CAPS LOCK key toggled the state of the CAPS LOCK light).
 
I put Schnurzels RT01 code into the PIC12F629 of an AT2XTKB connected to my IBM XT. I then used that AT2XTKB with the IBM 84-key keyboard supplied with early IBM AT's, and with a Honeywell keyboard. On both keyboards, the NUM LOCK, CAPS LOCK, SCROLL LOCK lights behaved as expected (e.g. each press of the CAPS LOCK key toggled the state of the CAPS LOCK light).


So I have verified that the NUM LOCK, CAPS LOCK, SCROLL LOCK lights actually do work on a different $5 USD PS/2 keyboard by proHT. But on a Compaq KB-0133 they do not with RT01 firmware but they work on both keyboards with the 0.94 firmware.

anyone have a clue of why RT01 is behaving differently on different PS/2 keyboards?
 
Last edited:
Hi Guys,

I got the AT2XTKBD circuit board some time back in the hopes of converting my XT Keyboard for use with my PC visa PS/2. I had understood that of course the code for the PIC needed to be changed as i had planned to use it the opposite of what it was intended for.

After looking at the code i realized that a whole LOT more needs changing besides the translation lookup table for the scan codes. Like for example the functions processing the signals from the host were all done assuming that the host was an XT computer, and the functions processing the input from the keyboard were assuming that from a AT Keyboard.

From looking at the AT2XTKBD.sch diagram, my idea was to hook up the PC to the current "PS/2_Keyboard" port and the XT keyboard to the "XT_HOST" port. And re code the code for the adapter. Is this feasible (hardware wise)?

Next thing i can't figure out is what is the purpose of Jumper 1? :confused:

I think before i attempt this i need to understand more on how a AT host, and a XT keyboard behaves. Can someone please point me to some documentation on these? I seem to easily find docs for AT keyboard but not much is found for XT Keyboard.

Thanks!

Hi, I also need this XT2 reverse adapter: I need to Connect an IBM Model F XT keyboard to a more "modern" board like a 286 or 386 AT. Have you had any success?
 
Hi guys, thread is a little confusing with the commentary of a few different projects & some links are dead now. What is the current source & schematic please??
 
Hi guys, thread is a little confusing with the commentary of a few different projects & some links are dead now. What is the current source & schematic please??

Circuit diagram

1. Goto post #1 at [here].
2. Use link: Schematic view #1

Parts list

Within post #1 at [here].

Version 0.94 code for PIC - Hex file for programmer

1. Goto post #1 at [here].
2. Use link: View attachment XTATKEY_094.zip

Version 0.94 code for PIC - Source listing

In [here].

Additional information

See [here].
 
Back
Top