IBM Model M2 keyboard error codes (LEDS)

Chuck Guzis cclist at
Tue Jun 8 16:11:51 CDT 2010

On 8 Jun 2010 at 20:13, Tony Duell wrote:

> The keyboard contains a microcotroller (8048 IIRC) which is reset by
> an RC network in the keybaord, it doesn't sue the system reset line. i
> suppose if the 5V line was risingtoo slowly, then the microcontroller
> may not initialise properly.

If it's connected to an AT+ system said PC normally sends out a RESET 
command to the keyboard.   This is pretty much required as there are 
some "autoswitching" (XT-AT mode) keyboards that will send out a 
continuous stream of wrong-parity ACKs until they receive either an 
XT-style reset (holding clock and data low for ~200 msec) or an AT 
response (porobably any command;  NAK or RESET will do).

It goes without saying that bizarre and wonderfully non-functional 
things happen if you plug an XT keyboard into an AT-or-better system 
or an AT keyboard into an XT system.


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