Changing CONFIGURATION word from within program

[btaylor]

Is it possible to re-write the configuration word once the chip (877A) has been loaded with a boot loader and soldered on the board?

I realise the config memory location is above the address range normally accessible but are there any tricks that might let me recover 20 boards with 877A thin quad flatpacks that need to have the WDT active but which were programmed with WDT OFF?

thanks
Brian

[Melanie]

Sorry to tell you, but the Config word is not accessible through your program in any way.

The only way is to solder-on leads for ICSP but bear in mind that a high voltage is applied to MCLR (easy if you have tied this to Vdd with a Resistor, just unsolder it), and that RB6/RB7 carries the programming data and clock so it shouldn't be loaded down with too much baggage. PIC will have +5v on it... so again, best to isolate it rather than power up your entire PCB. http://www.picbasic.co.uk/forum/attachment.php?attachmentid=68&d=1088530104

Other than that, it's time to make friends with your favourite desoldering tool...

[btaylor]

I ended up making up a programming harness than linked the target board to my EPIC programmer. Similar to your schematic except I found I had to groundthe LV Prog pin of the PIC16LF877A TQFN package. Only a couple of fixable shorts soldering to the fine pitch wires and all 20 boards recovered in the end.

By enabling the WDT I was able to use the PBP SLEEP command and drop the idle current draw from 120 uA down to 8 uA (including two 32 Mbit serial flash memories).