Franz Fasching wrote:
>
> Hi ev'rybody,
>
> I've troubles getting a home-built Tait-style 16F84 programmer to work,
> although I believe the hardware (parallel port, D0, D1 for programming, ACK
> for readback) to be correct (correct voltage of _MCLR during programming,
> correct Vdd and Vss, correct "0" and "1" levels at RB6 and RB7).
>
> I use the circuit with David Taits PP.EXE, and it verifies fine in debug mode
> (PPDEBUG=1, readback is o.k.), but during programming the very first word of
> WALK.HEX, PP.EXE stops with "error: read 03FF, expected 0186" or something
> like that. Now I'm wondering if not the programmer, but the 16F84 chip itself
> is faulty?
>
> Does anyone have a hint where I could start searching for the problem?
> I already tried various settings of PPDELAY and PPSETUP, but nothing works.
> Unfortunately I just have a logic probe, but no scope for testing.
> How can I test the 16F84 chip to be "good" or "bad", or further verify the
> programmer hardware without a scope?
>
> Thanks for your help,
> Franz
Greetings:
  You don't say how you power the circuit.  I have had similar problems
when using Tait-style programmers under battery power when the batteries
get weak.  It will read the PIC fine, and erase it fine but you will get
errors when you try to program it.

Jeff