PIC16F872 - RB6 / RB7

mhaas8 · Joined: 14 Jan 2007 Posts: 3

I need to utilize pins Pins RB6 and RB7 as standard I/O on the PIC16F872. I tried utilizing the NOLVP as shown below.

#fuses HS,NOWDT,NOLVP,NOPROTECT

However, this did not solve my problem. Any assistance would be greatly appreciated.

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

They should work. Are you using a debugger, such as CCS ICD-U40
or Microchip ICD2 ? If so, the debugger uses pins RB6 and RB7.
If you want to use them, then create a stand-alone program and
disconnect the debugger from your board.

mhaas8 · Joined: 14 Jan 2007 Posts: 3

Thank you for your reply. However, I am not using a debugger.

Pins RB6 and RB7 always go high and never change state.

As a note, I am using an older CCSC compiler, PCM 3.077, but that functionality is supported.

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

I don't have a 16F872 to test, so I made the program shown below,
which runs on a 16F877. I installed PCM vs. 3.077 and compiled it
with MPLAB vs. 5.70.40 (because that old compiler won't run on vs.
7.xx of MPLAB). I then used the ICD2 (with the modern MPLAB)
to program the Hex file into my PicDem2-Plus. It works. I looked
at pins B6 and B7 with an oscilloscope and they're toggling.

I then re-compiled the program below for the 16F872, with vs. 3.077.
I compared the .LST files for the 16F877 and the 16F872. They're
very similar. There's a little bit of differences in the delay_ms()
routine code, but they're basically the same. The code that sets
the TRIS and writes to Port B pins B6 and B7 is identical.

So it's my belief that there's nothing wrong with the code generated by
vs. 3.077 of the compiler. I believe you probably have a hardware
problem. You probably have some external circuits on pins B6 and
B7 (maybe that you aren't aware of), that are causing the problem.

Or, maybe you have the DEBUG fuse enabled, or something like that.
The fact that those pins are normally used by the debugger is a very
bigg clue. You should investigate that issue completely.

mhaas8 · Joined: 14 Jan 2007 Posts: 3

I will have to do some additional investigation. However, please know that I do appreciate the insight. Thank you.