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IBM model M on a IBM XT machine

offensive_Jerk

offensive_Jerk

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I should be recieving an IBM XT system shortly. I am curious, will a model M keyboard work with an XT?

I have the 1396434 variant. I just looked on Wikipedia, and it states there is only PS2 protocol.

Not sure if that means incompatibility.
 
offensive_Jerk said:
I should be recieving an IBM XT system shortly. I am curious, will a model M keyboard work with an XT?

I have the 1396434 variant. I just looked on Wikipedia, and it states there is only PS2 protocol.

Not sure if that means incompatibility.
Click to expand...

One way to figure out is to try it out. It will not damadge anything if it don't work.
 
The XT keyboard protocol is different from the PS/2 or AT protocol. PS/2 keyboards will work on AT machines and vice versa, the main difference is the 6 pin mini din connector (PS/2) and the 5 pin DIN connector (AT/XT).

If you plug a PS/2 or AT keyboard into an XT you get garbage when you type. Keyboards from that era may have a little switch on them to change their mode of operation (XT/AT), but that was taken out of them after XTs became less common.

Check out this thread for a convertor box (coming soon).
 
lutiana said:
The XT keyboard protocol is different from the PS/2 or AT protocol. PS/2 keyboards will work on AT machines and vice versa, the main difference is the 6 pin mini din connector (PS/2) and the 5 pin DIN connector (AT/XT).

If you plug a PS/2 or AT keyboard into an XT you get garbage when you type. Keyboards from that era may have a little switch on them to change their mode of operation (XT/AT), but that was taken out of them after XTs became less common.

Check out this thread for a convertor box (coming soon).
Click to expand...

Some keyboards are autosense, and therse will both work when connected to an XT or AT. Several of the Model M were, and I have confirmed that the Commodore PC 30/40 III are too. For some reason therse keyboards will have problems working in a PC, but I thinks this has something to do with Open-collector lines VS. normal TTL lines (the interface of the XT is OC, that's for sure).
 
Very true, but it does need to be said that the auto sense on these keyboards only works with the newer versions of the XT Bios.
 
lutiana said:
Very true, but it does need to be said that the auto sense on these keyboards only works with the newer versions of the XT Bios.
Click to expand...

Not the Commodore keyboard (for some reason). I have sucessfully used the very same Commodore PC keboard with both a Pentium from 1994 and a true-blue IBM 5160 PC/XT with the earliest BIOS dated 1982. I did not have to change anything (The Num-lock/Caps-lock/Scroll-lock leds even works, but I do not know to what degree)!
 
per said:
For some reason therse keyboards will have problems working in a PC, but I thinks this has something to do with Open-collector lines VS. normal TTL lines (the interface of the XT is OC, that's for sure).
Click to expand...

I have done some researching, and I figured the following:

The IBM 5150 PC and Type 1 keyboard uses 74LS125 tristate buffers with grounded inputs on the keyboard clock and data line. The controlling input is connected to the trigger of the buffer, and this means that when the signal to one of therse buffers are high, it gets tristated (rigth in between High and Low). When the controlling input is low, the line is grounded. There is pull-up resistors on both lines, so the two possible states are (1) grounded, or (2) tristated and default high if all inputs are tristated.

The IBM 5160 PC/XT and Type 2 keyboard uses 74LS07 Open-Collector buffers on the keyboard data and clock lines. Those can't be inactive, and therefore they will , they provide a proper High signal. the possible states are about the same as with the IBM 5150 PC, but based on Open collector instead of tristating hence they sink more current (I think).

What I think may be the cause with Model M keyboards, is that there is most problably an POST routine in the late revision of the BIOS that sends a signal over the clock line to the Model M keyboard, telling it to switch over to XT-mode. If this is not the cause, it may look at the current of the data/clock line and determine if it macthes the Open Collector interface of the XT.
 
An early IBM Model M will work on both XT and AT machines. "Official" XT Model M's had the LED panel blanked off. Plug it in and cross your fingers!
 
dongfeng said:
An early IBM Model M will work on both XT and AT machines. "Official" XT Model M's had the LED panel blanked off. Plug it in and cross your fingers!
Click to expand...

In fact, I've got an 102-key IBM PS/2 keyboard (Model M, 1391409) from 1991, and it actually worked in my early-BIOS XT too! However, as expected, the LED's doesn't work.

It's strange that the LED's are actually active on Commodore PC XT/AT keyboars working in XT-mode. Does any other AT/XT switchable keyboards do this?
 
Last edited:
per said:
In fact, I've got an 102-key IBM PS/2 keyboard (Model M, 1391409) from 1991, and it actually worked in my early-BIOS XT too! However, as expected, the LED's doesn't work.

It's strange that the LED's are actually active on Commodore PC XT/AT keyboars working in XT-mode. Does any other AT/XT switchable keyboards do this?
Click to expand...

I have a Laser AT/XT with Alps keyswitches which, if I remember correctly, DOES have functioning LEDs in XT mode. However, it is possible for them to go out-of-sync with the actual functions they represent, because the XT keyboard interface is unidirectional so the computer can't tell the keyboard what status each lock is.
 
per said:
In fact, I've got an 102-key IBM PS/2 keyboard (Model M, 1391409) from 1991, and it actually worked in my early-BIOS XT too! However, as expected, the LED's doesn't work.
Click to expand...

My Modem M works on my all 5150 and 5160 machines!

How? Well, it is UK layout, so I need to load a driver in autoexec.bat. Usually this would be:

Code: 
c:\dos\keybuk.com

But for the Enhanced layout you need to load that with a "/e" at the end:

Code: 
c:\dos\keybuk.com /e

It will work perfectly on any IBM! This is in PC DOS 3.2, the driver is not included in 2.x, which is a bit strange.

per said:
It's strange that the LED's are actually active on Commodore PC XT/AT keyboars working in XT-mode. Does any other AT/XT switchable keyboards do this?
Click to expand...

I have a couple of clone ones that do that. However, I think it is controlled by the keyboard circuits, rather than the PC itself. Sometimes they have switched the wrong way round!
 
per said:
It's strange that the LED's are actually active on Commodore PC XT/AT keyboars working in XT-mode. Does any other AT/XT switchable keyboards do this?
Click to expand...
I reckon ALL keyboards with XT/AT switch underneath (eg. KB-6251ER made by Taiwanese NAN TAN COMPUTER CO.) I've seen have special support for LEDs in XT mode.
So once I was surprised to see that auto-switching IBM Model M keyboard to remain dark when connected to an XT...
 
This may actually be related to another current thread. As much data needs to be provided as possible in these cases (for a possible compilation). Part numbers, SDL or fixed cable, lock LEDs or not, and dates of manufacture.

How about it?...
 
Like I posted before mine is a 1396434
I guess it was used for airline people, as there are other markings on the keys
Detachable cable.
manufactured 26may88.
Round IBM logo
 
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