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PICList Thread
'Reading PIC RAM with PSP'
2000\03\30@193638 by Jinx

face picon face
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 ?


2000\03\31@033445 by Alan B Pearce

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Why not program up your code into one of the newer micros with bigger ROM space
and more i/o pins, and then mount the chip on a header that will plug into your
original hardware? This would allow you to have a breakpoint switch and serial

2000\03\31@100652 by M. Adam Davis

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


Jinx wrote:
{Quote hidden}

2000\03\31@124602 by jamesnewton

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James Newton (PICList Admin #3) 1-619-652-0593
PIC/PICList FAQ: or .org

{Original Message removed}

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