Today I sort of got the 16F876 to do some A/D work, or at least what appears
to be useful results.  I put some LEDs
on some of the port C pins (I only have 4 available so I chose bit 0, 2, 3,
and 4) and I put a pot from +5 to 0 on
analog channel 0 and the LEDs  do change their pattern as I change the
analog input, but there's some things I still don't know how to figure out
about the program.

The LEDs don't stay lit, they just flash quickly on and then stay off for a
while and then flash on quickly again (with the same or updated data) and I
can't decide if the program is somehow setup to do this purposely or if
there is something I should know otherwise.  I would have expected the ports
to latch the samples so the LEDs are always on with the current sample data,
not flashing with it, so I was wondering what might cause it.  I thought I
found some possible reasons for this in the original demo file I was using
so I commented some things out but it still does the same thing.  I first
commented out a line that looks like it clears port C right after storing
the sample data on the port so I thought, no wonder it is only flashing if
it writes to the port and then clears it in the next line...but taking that
out didn't help...then I wondered what is the use of the "WaitPush" loop
that does something on port B....I thought maybe it wants port B to be doing
something for it to latch port C....so I tried tieing all pins of port B
high, then low, then some high and some low and all it did was change the
rate of port C flashing data LEDs.  So I commented out the whole loop and
expected that the program would just sample the input, write it to the port,
then immediately resample the input and update the port so that the lights
would always be on with the data and would only change when the input level
changed....but still all I get is flashing data, not latched output data.

I appended the demo file here again with the commented out portions, hoping
someone can look at it and tell me if it should be latched data or if there
is a reason it's flashing, and if I should uncomment some of that stuff
again to make it work better.

All I ever wanted was a simple program to read the analog port and store the
binary on the port so I can see that it changes the leds when I change the
pot, but this flashing thing is making me wonder if I did something wrong.

I ended up using just an RC combination on OSC1 still instead of a crystal
if that is necessary information at all.  And yeah, regarding that previous
thread about the internal RC.....when I first tried this yesterday I had
nothing on the OSC pins and the circuit didn't do anything so I didn't even
have noise clocking it...now I have SOMETHING.


;DEMO file from MPlab files, modified slightly

     list p=16f876
     include "p16f876.inc"

     org 0x000
     nop
Start
     banksel PORTC
     clrf PORTC                  ;Clear PORTC
     movlw B'11000001'     ;RC, A/D enabled
     movwf ADCON0

     banksel OPTION_REG
     movlw B'10000111'     ;TMR0 prescaler, 1:256
     movwf OPTION_REG
     clrf TRISC                    ;PORTC all outputs
     movlw B'00001110'      ;Left justify,1 analog channel
     movwf ADCON1          ;VDD and VSS references

     banksel PORTC

Main
     btfss INTCON,T0IF     ;Wait for Timer0 to timeout
     goto Main
     bcf INTCON,T0IF

     bsf ADCON0,GO         ;Start A/D conversion
Wait
     btfss PIR1,ADIF             ;Wait for conversion to complete
     goto Wait

     movf ADRESH,W         ;Write A/D result to PORTC
     movwf PORTC

     ;clrf PORTC
 ;WaitPush
     ;btfss PORTB,0
     ;goto WaitPush
 ;movwf PORTC

 goto Main
 end