Possible to correct this error on board layout?

[wdmagic]

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.

[Demon]

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

[wdmagic]

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.

[Acetronics2]

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.


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

[HenrikOlsson]

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.

[Dick Ivers]

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.

[wdmagic]

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 :)