Nick Bedbury wrote:
> I am having a problem connecting to a PIC18F87J50.  I constantly read
> a device ID of 0x0000.

That indicates a communication problem between the programmer and the PIC.

Which programmer are you using?

> When looking at the PGC and PGD data during a connect,
> it seems like there is some capacitance between the signal lines and
> ground.  Both the clock and data signals
> slowly decrease in voltage magnitude throughout an attempted
> connection/program
> operation to the PIC.

That makes very little sense.  Maybe some connection is not really connecte=
d
somewhere.  It sounds like things are floating.

> I added decoupling capacitors between power
> and ground, which temporarily fixed the problem.

Whoa, you mean you didn't have them in there in the first place!!?  Why
would you build a PIC circuit without decoupling caps?  All the grounds nee=
d
to be solidly tied together close to the PIC too.  What kind of decoupling
cap did you use?  Ceramic, electrolytic, something else?  What size?

When you said the programming lines were slowly floating earlier, did you
have the scope probe ground connected.  Normally that would be a stupid
question, but not when someone tried to get away without decoupling caps.

> ... breadboard circuit ...

This is starting to smell more and more like a flaky connection.

> Now that I have resumed working, again I am
> reading a device ID of 0x0000 with no luck.

What do PGC and PGD look like now?  What are Vdd and MCLR doing during
programming?  Do they look different at the programmer than at the PIC.

> Previously, the PIC would not connect unless I temporarily probed the
> programming pins with an o-scope.

Yikes, you've got some serious problem there.  Are you really sure MCLR or
PGM aren't floating?  Don't just say they shouldn't be, actually verify it
with a scope probing right at the PIC pin, not some other place it's
supposed to be connected to.


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