Yes, I realize the two are quite different in the way they are programmed,
and I thought I had all my problems solved, but here I go again.

I've designed a serial port based production programmer for the midrange
pics. I am able to program the 16F84, and to read it at the variable
voltages required of a production programmer.  I've been trying to read and
program the 16C71 but I'm having absolutely no luck.

According to my reading of the programming data sheets, the algorithm for
reading the 16F84 and 16C71 are *exactly* the same.  How can it be that I
can read the 'F84 but not the 'C71?

If I look at the 'F84 on a scope, I see the command issued to the pic, a
little rise as the PIC (being read) changes from high impedance input to
low impedance output, then the data is clocked out.  On the other hand, if
I look at the 'C71, it appears the command is never accepted, so the data
never comes out, and there is no telltale bump as the the pin changes from
input to output.

Could it be that the 'C71 and 'F84 have different technologies driving
their inputs and outputs?  I've tried adjusting the resistors on the open
collector pull-ups on RB7 (data I/O), but that has not affected anything.

Can anyone offer any pointers? A kick in the pants in the right direction?

To those that help me out, I continue with my offer of a
coffee/tea/soda/beer on your next trip to the Washington D.C. area.


About my programmer:

I was inspired to make this programmer since I can't seem to get any of the
parallel port programmers, or the PICStart Plus, to work under Windows NT.
I set out to develop a stand-alone (except for the terminal) production
programmer for the mid-range PICs.  Once I'm confident enough in it, I'm
going to offer the design up as freeware.  I've started to write the
driving code in Perl, so if it all goes according to plan, this programmer
should work on any system that has a serial port and a version of Perl that
can talk to the serial port.

Yes, there are many programmers out there, but few (free) production
programmers, and heck, I wanted to learn something, not just copy someone
else's design.  Now I'm regretting that decision :)

Matt

-----------------------------
Matt Bennett                |
mjb@hazmat.com              |
http://www.hazmat.com/~mjb/ |