Hi all

I'm working on a project based on this

http://home.clear.net.nz/pages/joecolquitt/pic_keyboard.html

The intention is to monitor/capture/transmit keypresses of the
PC keyboard, using a PIC circuit between the keyboard and the
PC. Although it can be added in parallel

A problem has arisen which has me stumped. The keyboard
freezes when the PIC transmits a character down to the PC.
The PC still recognises and displays any further characters
sent by the PIC, so the clock and data lines are still working

As far as I can tell, according to the pdf linked to on the page,
the PIC transmission is within timing specs (as evidenced by
the PC recognising characters sent). On occassion I've had
the PIC emulate the timing exactly but the keyboard still stops

As I understand it, PC keyboard outputs are open-collector
or open-drain with pullups to Vcc. My grounding transistors
are in parallel with those, which I wouldn't have thought to be
a problem. I've also tried disconnecting the keyboard during
a PIC transmission using 4066 switches but no luck

I see no glitches on data, clock or Vcc, and there's no sequence
which would put the keyboard in a state to receive commands.
All I see is a character going to the PC from the PIC

Any thoughts ? When it's sorted out I'll put the relevant parts up
as a project/reference on PIClist

TIA

Joe

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