My guess:  You have a short in there somewhere.  That's an OC or OD
(open collector or open drain) driver, should never be held low like
that...  Pulled low sometimes when toggling the clock line, yes, but not
always.  Your pull-up resistor's tested good, I assume <G>

Cycling power should cause some activity from the keyboard (LED's should
flash and a little more) - NEVER should data be held low, as then the
host computer cannot talk TO the keyboard.  Something's wrong.

  Mark

John Hansen wrote:
> I'm working on a project that involves interfacing an AT keyboard with a
> PIC.  I'm following the documentation on
> http://www.beyondlogic.org/keyboard/keybrd.htm
> I've applied 5 volts to the keyboard and placed pull-up resistors across
> both the data and clock lines from the keyboard.  When I look at the clock
> output on a scope, I get just what I'd expect.  Looking at the data line,
> however, always produces a low logic level.  This occurs even when I don't
> have the data and clock lines attached to anything (except the
> pull-ups).  Something in the keyboard is clearly pulling the data line low
> and keeping there.  Pushing keys on the keyboard doesn't change anything,
> the data line stays low.  Is it necessary to send a sequence to the
> keyboard to get it to wake up and start sending data in response to
> keypresses?  Thanks in advance for any assistance you might be able to provide.
>
> John Hansen

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