> I'm working on a project based on this
>=20
> http://home.clear.net.nz/pages/joecolquitt/pic_keyboard.html
>=20
> 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
>=20
> 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
>=20
> 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
>=20
> 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
>=20
> 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
>=20
> Any thoughts ? When it's sorted out I'll put the relevant parts up
> as a project/reference on PIClist

I suspect the keyboard is seeing the characters you are sending as
commands to the keyboard, but as it doesn't know what to do with them it
goes into dumb mode.

But then I thought this was how barcode scanners and the like worked, so
that doesn't make sense either ...
--=20
Scanned by iCritical.

--=20
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