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using a 16F688, my board got made with a led hooked to pin 4 instead of pin 2, it needs to light on pin high but since #4 is a in only.... future boards will be corrected but on the ones I have now there is no place to cut trace and jumper, what is available is to jumper pins 2 & 4. NOW I am not using MCLR and the program doesnt access pin 4 for anything. So...
Can I send lows and highs out on pin 2 (shorted to pin 4) with #4 connected to LED+ ?
code was already written for Pin 2 to LED.
I'd cut pin 4 and bridge a single-strand wire to pin 2 (the leads cut off a LED work nicely for short hops).
Like the time I forgot the resistors on 2 columns of LEDs, d'uh! I cut the traces and bridged the resistors. Not elegant but it worked.
Short answer; whatever works. :)
Robert
thanks, I cant cut pins, customer would notice. I am using a IC socket, so I was going to use circuit trace repair strips to jumper 2 & 4 under the socket. hidden by socket and chip. and its not really modifying the existing board, its just adding to it. this is a example circuit to show my work, I dont wanna show any errors if possible. I was just wondering what would happen if the MCLR pin, even though MCLR is disabled, would cause the code/program to do weird stuff.
I dont want to turn it on till I know for sure as I only have 1 of this chip right now.
Quote:
Originally Posted by wdmagic
of course you can ... moreover if pin 4 never can turn into an output ! :rolleyes:
I remember some Genuine Microchip reference designs using this feature ... ( especially the " 50 Mhz frequ. counter " using a 16F84 ... )
Alain
Hi,
As long as MCLR is disabled I can't see any problems doing that once the circuit is in its normal operating mode.
However, if you're programming the PIC in circuit it might be a problem since MCLR is also the Vpp pin which you now have jumpered to a "normal" pin. I don't know for sure if this would be a problem but I think it might.
The internal protection diode on "the other pin" would clamp the voltage applied to the MCLR-pin by the programmer to just above Vdd which would prevent the PIC from entering programming mode. Using a diode as the "jumper" from RA5 to MCLR would protect RA5 from the high voltage applied to the MCLR-pin during programming. Or, perhaps, use Low Voltage Programming - I've never used it though.
Obviosuly, if you're NOT programming the PIC in circuit then I can't see any obvious issues.
May require some investigation/testing.
/Henrik.
Henrick,
wdmagic said he is using a socket. I think that means he can do his programming off board. You are correct that ICSP would not work with the programming pin jumpered to another pin. I know from experience. A Pickit 2 programmer will stop and send an error message when attempting to program with jumpered pins.
Ok thanks everyone, yes this circuit is programmed offboard. and the new boards dont have this issue just this one. thanks for the info.
and thanks for the info on ICSP I forgot about that, its good Im not using that :)