I am in the middle of a design using a 12C508A (highly cost sensitive). As
part of the manufacturing process, I am going to need to run a special
calibration mode of the PIC's program. This will be followed by programming
a couple of previously unused locations with RETLW instructions containing
the calibration constants.

I intend to perform the calibration using the same physical interface as
ICSP. However, the program will be running on the PIC and will interact with
the calibration/programming station using a simple serial protocol.

GP3 will have 3 possible states:
Pulled to Vpp to enter programming mode.
Pulled to ground to enter calibration mode.
Left floating so the built-in pullup will pull it high for normal operating
mode.

What I need is an ICSP programmer design with available source code, so that
I can add commands to the programmer to perform the calibration (ie: pull
GP3 down to indicate calibration mode, then use the same clock and data
lines as ICSP uses to communicate with the PIC to perform the calibration).
After the calibration constants are determined then the program will reset
the PIC, raise GP3 to Vpp and burn in the calibration constants in as
RETLW's.

Is there source code available for a PIC-based ICSP programmer for the
12C508(A)?

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

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