I know its basic, but have your CORRECTLY set the ADCON register? Last
month I was developing code for '877 and I reached your same problem. It
was solved changing the ADCON register.

Another thing: When you execute an toggle routine or command, the pic
reads the pin contents, then togle a bit and shifts out it again to the
pin, so, depending on your hardware (an led drawing a lot of current for
example), when the pic reads the pin, the "hi" (an 1) voltage on it is
below, let's say 2.5v; so the read is interpreted as a low rather then a
high. If it happens, the real behavior is that the pin don't toggle. It
also happened to me last month.

If it helps, reply so I may track this "interesting" behavior.

see you,
             Beto.




______________
I believe I've just found a really nasty hardware bug in the 16F876.  I
figure I would tell you guys first then figure out who at MChip to give
a
piece of my mind.

Here's the scenario : I'm using pin 0 of port A to wakeup an external
device.  This involves toggling the pin.  If only pin 0 is written to, a
0
never comes out on the port.  To get it to write something another pin
on
port A must also be written to.

My bare bones software test cases are :
1: xor pin 0 with 1
2: delay

In this case pin 0 stays a 1, constantly.  If I change it to :

1: xor pin 0 with 1
2: delay
3: write a 1 to pin 1,2,3 or 5;
4: write a 0 to pin 1,2,3, or 5;

Then it works.  Otherwise nix.  It operates in exactly the same manner
with
bsf and bcf on that particular pin.  I didn't see anything in the errata
on
this.  I'm more than a bit irritated.  If someone can show me how this
is a
bug on my part I'd be grateful (as well as surprised).

Here's the source for working :

m015    MOVLW .1
00F0 1283  0529         BCF   0x03,RP0
00F1 1303  0530         BCF   0x03,RP1
00F2 0685  0531         XORWF PORTA,1
00F3 0000  0533         NOP
00F4 0000  0535         NOP
00F5 0000  0537         NOP
00F6 0000  0539         NOP
00F7 0000  0541         NOP
00F8 1685  0544         BSF   PORTA,5
00F9 1285  0546         BCF   PORTA,5
00FA 28EF  0549         GOTO  m015

And for not working :
m015    MOVLW .1
00F0 1283  0529         BCF   0x03,RP0
00F1 1303  0530         BCF   0x03,RP1
00F2 0685  0531         XORWF PORTA,1
00F3 0000  0533         NOP
00F4 0000  0535         NOP
00F5 0000  0537         NOP
00F6 0000  0539         NOP
00F7 0000  0541         NOP
00F8 28EF  0547         GOTO  m015

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