IBM Model M2 keyboard error codes (LEDS)

[Tony Duell]

> 
> 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 

That is not the same thing at all. The serial command/data transfer 
to/from the system is bit-banged by the microcontroller, so the 
microcontroller must be running its firmware correctly to handle that 
RESET command. Yes there is such a command which initialises various 
parameters of the keyboard, but it's not what I was thinking of.

I was thinking of the hardware reset to the microcontroller that causes 
it to run the firmware in the first place. The reset pin of the 8048 is 
connecvted to an RC network in the keyboard, not to the hardware reset 
signal in the host system (strangely, at least on XT machines, pin 3 of 
the DIN connector (labelled as 'reserverd') did carry the system reset 
line, but no IBM keyboard used it. I don't think it's connected at all in 
AT machines.

If the microcontroller does not reset properly, then it will not be able 
to accept any commands from the host.

-tony