The picstart plus won't read RAM.  The best way to read the RAM is to use one
pin as a serial output, and every so often send the contents of the ram out it.

Otherwise, use a 16f876 and the free ICD.  You'll be able to troubleshoot the
'f84 with the 'f876

-Adam

Jinx wrote:
>
> I'm trying to get to the bottom of a PIC h/w problem. I haven't got
> a h/w emulator (grrrrr) and wonder if what I propose to do with a
> Picstart Plus unit is possible.
>
> What I've been doing up until now is removing the PIC from the
> circuit and reading the EEPROM contents with the PSP. There
> are some points in the s/w where I used to be able to stop the
> flow and write some RAM to EEPROM. However, the s/w has
> grown quite complex and that method is no longer easily do-able
> and I can't free up a pin for a "freeze" pushbutton without affecting
> the data.
>
> I'd like to take the PIC out of the circuit it's in, with a Lithium cell
> (+ diode) on it to keep the RAM alive, and drop it into a PSP so that
> I can read both the RAM and EEPROM contents. But looking at
> MPLAB 3.99.06 I don't see a window for displaying read RAM. Do
> later versions cater for this or is what I'm hoping to do too off-the-wall ?
>
> I've previously bit-banged the RAM / EEPROM contents out using
> two spare pins with a Motorola EVM and that worked OK, but now
> those last two pins are being used. Besides, because of the dynamic
> nature of the circuit and the way the s/w is growing, it's getting tedious
> to keep putting break points in at various places to make the s/w halt
> at the right moment and then jump to a serial i/o routine.
>
> Ideally what I'd like to do is
>
> (a) h/w switch the xtal out to freeze the PIC
> (b) turn the power off, keeping RAM contents intact with the Li cell
> (c) drop the PIC into the PSP and read it, assuming that a RAM
>      read is possible and displayable
>
> Any thoughts ?
>
> TIA