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-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Jinx
Sent: Thursday, March 30, 2000 16:37
To: PICLIST@MITVMA.MIT.EDU
Subject: Reading PIC RAM with PSP


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