Al Williams wrote:

> Ah... I hadn't noticed that. So that means my erase is probably
> working.
> Then the only problem is that if I burn the fuse word, when I do a
> read
> after a reset, I read location 1 instead of 0! I can do everything
> except
> the burn of the fuse (even IDs) and it comes up with location 0. If I
> burn
> the fuse, I get location 1. Very strange. Oh well, I'm sure I will
> work it
> out.
>

Dear Al

This problem is not described in 16c84 programming specs. But an answer
is in progamming specifications of other PIC (do not remember which
exactly). I faced with it when built my own programmer. The problem is
in entering programming mode. Being more precise - voltage on MCLR pin
rises not as fast as it should. This result in PC counter increments and
you read location 1 instead of 0. As for configuration memory this does
not matter since you use additional command to enter this mode which
sets PC to 2000. When configuration word is not programmed the
oscillator is configured fo RC and does not work with crystal.when you
programm it you get this fucking increment.
There are two ways to avoid those increments: 1 slow down your PIC or
stop it (in case of in-circuit programming). 2 change your MCLR
circuitry which applies 12 V ( open collector with 10 K pull-up resistor
which I see on many programmers is not enough for in-circuit programming
even if PIC run @ 4 MGz). I redused pull-up to 1 K and this work up
until 10 MGz.

Regards
Vassili