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JBM
Joined: 12 May 2004
Posts: 54
Location: edinburgh, Scotland
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| PIC16F88 comparator |
 Posted: Wed Mar 08, 2006 3:03 pm |
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I'm trying to use the PIC16F88's internal comparator, but so far, no joy.
Here's my code:
| Code: | #include <16F88.h>
#fuses INTRC_IO, NOWDT, NOPROTECT, BROWNOUT, PUT, NOLVP
#use delay(clock=8000000)
void main(void)
{
setup_oscillator(OSC_8MHZ);
setup_comparator(A0_VR_A1_VR); // Comparator mode 2
setup_vref(0xC0 | 9);
while(1){
output_bit(PIN_B5,C1OUT);
delay_ms(100);
}
} |
it should be strikingly similar to the code here, but isn't identical. This is beacuse my version of PCM is about 2 years old (version 3.184), which is likely to be where my problem is.
If that isn't the case, what am I doing wrong? I've got the voltage reference oupoutting fine on A2, but no matter what my voltage on A0 is, C1OUT is always 0.
Any ideas?
-JBM |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Wed Mar 08, 2006 3:28 pm |
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In your version of the compiler, the wrong address is used
for the CMCON register.
Here is the code for your version:
| Code: |
... setup_comparator(A0_VR_A1_VR); // Comparator mode 2
0028: MOVLW 02
0029: BCF 03.5 // Bank 0
002A: MOVWF 1F // Wrong address for CMCON
002B: BSF 03.5 // Bank 1
002C: MOVF 05,W // Read TRISA
002D: IORLW 03 // Set A0 and A1 as inputs
002E: MOVWF 05 // Write to TRISA
002F: MOVLW 06 // Do a short delay
0030: MOVWF 77
0031: DECFSZ 77,F
0032: GOTO 031
0033: NOP
0034: BCF 03.5 // Bank 0
0035: MOVF 1F,W // Read the wrong register
0036: BCF 0D.6 // Clear the CMIF bit
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Here is the code for PCM vs. 3.245:
| Code: |
... setup_comparator(A0_VR_A1_VR); // Comparator mode 2
// Note: Bank 1 is already selected.
0027: MOVLW 02
0028: MOVWF 1C // Set CMCON (0x9c) = 0x02
0029: MOVF 05,W // Read TRISA
002A: IORLW 03
002B: MOVWF 05 // Set A0 and A1 = inputws
002C: MOVLW 06 // Do a short delay
002D: MOVWF 77
002E: DECFSZ 77,F
002F: GOTO 02E
0030: NOP
0031: MOVF 1C,W // Read CMCON
0032: BCF 03.5 // Bank 0
0033: BCF 0D.6 // Clear the CMIF bit
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You could fix this by writing to CMCON directly with a line of code.
Define the address with a #byte statement. |
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JBM
Joined: 12 May 2004
Posts: 54
Location: edinburgh, Scotland
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| Posted: Wed Mar 08, 2006 3:30 pm |
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PCM, you never cease to amaze me.
Thanks a million.
-JBM |
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