On Thu, 23 Sep 2004 11:07:38 +0100, you wrote:

>Does anyone know of any issues that might be preventing some PIC16LF819's
>being reprogammed in-circuit, using a Microchip ICD2 programmer?
>
>I have 20 boards each with a PIC16LF819 (SOIC) soldered in. They all
>programmed without any problems first time around. I then needed to
>reprogram them and 17 reprogrammed fine, but 3 failed. In fact they fail at
>the first of the programming cycle, the Part Erase. Even though the erase
>reports that it succeeded, it takes a lot longer than it should (5 seconds
>instead of few hundred ms) and a subsequent blank check says it failed.
>Everything I have tried so far has not got them to reprogram.
>
>The config bit settings as shown by MPLAB (v6.60) for the original and
>reprogramming are:
>  Oscillator:           INTRC-RA6 is Port I/O
>  Wathdog Timer:        Off
>  Power Up Timer:       On
>  MCLR Select Bit:      RA5 is MCLR
>  Brown Out Detect:     Off
>  Low Voltage Program:  Disabled
>  Data EE Read Protect: Disabled
>  Flash Program Write:  Write Protection Disabled
>  CCP1 Mux:             RB2
>  Code Protect:         Enabled - All protected
>
>I have desoldered all the peripherals components in case they were causing
>the trouble. So now the only connections to the Vpp, PGC and PGD pins are
>from the board's programming header, but the reprogramming still fails.
>
>I've buzzed through and checked for shorts but no problems found.
>
>I have tried selecting power from the ICD2 and also power from the board -
>no luck erasing/reprogramming either way.
>
>Checking the signals on a scope: Vdd is 5V (if powered from the ICD2) or
>3.3V (if powered from the board); During programming Vpp reaches 13.5V (rise
>time of 70ns approx); PGC and PGD both produce good squarewaves between 0V
>and Vdd.
>
>I've tried a couple of other ideas I've come across - adding a pull-down of
>1k to the Vpp line, and also a pull-up of 1k to the same line (on a
>different occassion) but with no success.
>
>Could anyone please offer any suggestions as to how to get these
>PIC16LF819's to erase and reprogram? BTW - the codespace is totally full,
>otherwise I guess I could include a bootloader to get around this. Also, if
>another programmer is likely to work better for this than the ICD2 then I'm
>willing to get one.
>
>Very many thanks,
>
>James

I'm not sure it applies to this part, but I know the 12F parts are sensitive to Vcc risetime, which
can cause problems when there is capacitance or other loading on the supply.  

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