Dear Piclisters,

I am trying to use an EPP parallel port to transfer data from my
PIC-O'Scope to my PC and I am having trouble. I am using a PDF file
documentation which I got from some web site (I can't remember where) but
it isn't clear about some things. Let me ask a few questions and maybe
someone will know some answers:

1) The nWAIT line is the only handshaking line (out of three) which is in
input to the PC. It seems, however, to have a 1k (about) pull up to 5v
internally in the PC. Is this what it should be, or am I doing something
wrong, or (worse) is this maybe a quirk in my PC?

2) One of the pins on the pic is connected to this nWAIT line. It is
supposed to pulse high and then low again for about 1us to ack the EPP
port data transfer. I don't have a scope fast enough to see this very
well, but if I hook up a 115MHz counter chip to it, I actually see about
three pulses when it should have only pulsed once. If I disconnect the
line from the PIC and just measure the output of the pic, I get only 1
pulse, just as I should. If I hook up a long wire from the pic pin and
terminate it in a 1.5k resistor, I still only see 1 pulse, as it should
be. However, when it gets hooked up to the actual nWAIT line on the
parallel port, it goes wacky. This happens both with a 4 foot cable
between the PC and the PIC, and also even if I reduce the cable to 1 foot.
If I buffer this line with a pair of 7404s (one right after the other so
it is not inverting), I get only 1 pulse if I measure the pic pin, but I
get erratic (somewhere around 3 pulses) if I look at the output of the
buffer. I also tried using pin RA4 (open collector) with a small pull up
(1k), thinking that this might give the pic a better ability to drive the
line: same results, several pulses instead of one.

3) The code on the pic is supposed to read in a character from the EPP
port and send it back again. The PC software is acting as if it is being
properly ack'd, and it is receiving the proper character. However,
if I ,for example,send the letter A (or any ascii character for
that matter) and then send B, I'll get A back for both of them, and then
B back for the next one (in other words, I'm not sure if the acking is
occuring at the right time or if it is staying in sync).

I'm sorry to be so long winded and confusing, but I have been working on
this on and off for a few months, and I have been at it very intensily
these past few days and I think I have traced my problem down to this,
and I'd appreciate it if someone could either answer my questions or
point me to a better tutorial.

Thanks very much,

Sean