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Hi, all.
I was going through some of the programs I wrote for a course when I was in college 20 years ago, and I got curious about something. I made an analog comparator with the PIC12F629, and I want to change some of the code and the circuit. Before someone says the PIC12F629 is obsolete, again, this is something I did 20 years ago and I just want to tweak it a little bit for fun. I have some PIC12F629 microcontrollers from back then, so I'm not going to buy a modern microcontroller for this.
This is the circuit I made. Turning the potentiometer on GP0 turns the LED on GP5 on and off depending on the reference voltage on GP1 .
This is the code I wrote, which works fine:
I'm setting CM2-0 to 010, which is the setup where the comparator's output is not connected to anything. That's why in the main loop, I read the value of COUT, I put in VGPIO, which is a memory address (0x20), and then put that in the GPIO. This works fine, but I was looking at the PIC12F629 datasheet to understand the code, and I realized that it would had been easier to just set CM2-0 to 001, which connects the output of the comparator to GP2, and then put the LED on GP2. So I wrote this new code (I highlight the lines that are different after the code):
Differences:
1) MOVLW ~(1<<2) ;GP2 IS OUTPUT (instead of MOVLW ~(1<<5))
2) MOVLW 0<<CINV|b'001' (instead of MOVLW 0<<CINV|b'010')
3) The MAINLOOP is empty.
In this code, the main loop is empty because supposedly, the output comparator is directly connected to GP2, which is where I put the LED now. However, no matter how much I turn the potentiometer, the LED is always on. What am I doing wrong?
I was going through some of the programs I wrote for a course when I was in college 20 years ago, and I got curious about something. I made an analog comparator with the PIC12F629, and I want to change some of the code and the circuit. Before someone says the PIC12F629 is obsolete, again, this is something I did 20 years ago and I just want to tweak it a little bit for fun. I have some PIC12F629 microcontrollers from back then, so I'm not going to buy a modern microcontroller for this.
This is the circuit I made. Turning the potentiometer on GP0 turns the LED on GP5 on and off depending on the reference voltage on GP1 .
This is the code I wrote, which works fine:
Code:
;**********************************************************************
; VARIABLES
;**********************************************************************
CBLOCK 0x20 ;20h is the first file of the General Purpose Registers
VGPIO ;Virtual GPIO
ENDC
;**********************************************************************
; CODE STARTS
;**********************************************************************
ORG 0 ;reset vector
GOTO BEGIN
;**********************************************************************
; PROGRAM BEGIN
;**********************************************************************
BEGIN
MOVLW ~(1<<5) ;GP5 IS OUTPUT
BANKSEL TRISIO
MOVWF TRISIO
;CONFIGURE COMPARATOR
MOVLW 0<<CINV|b'010'
;SELECT MODE 2 (CM=010)
; +REF IS CIN+, -REF IS CIN-,
; COMPARATOR ON, NO EXTERNAL OUTPUT
;OUTPUT NOT INVERTED (CINV=0)
; -> COUT=1 IF CIN+ > CIN-
BANKSEL CMCON
MOVWF CMCON
MAINLOOP
;DISPLAY COMPARATOR OUTPUT
CLRF VGPIO ;ASSUME COUT=0 (LED OFF)
BANKSEL CMCON
BTFSC CMCON, COUT ;IF COMPARATOR OUTPUT HIGH
BSF VGPIO, 5 ;TURN ON LED
MOVF VGPIO, W ;COPY VIRTUAL GPIO TO GPIO
BANKSEL GPIO
MOVWF GPIO
GOTO MAINLOOP
END
Code:
;**********************************************************************
; VARIABLES
;**********************************************************************
CBLOCK 0x20 ;20h is the first file of the General Purpose Registers
VGPIO ;Virtual GPIO
ENDC
;**********************************************************************
; CODE STARTS
;**********************************************************************
ORG 0 ;reset vector
GOTO BEGIN
;**********************************************************************
; PROGRAM BEGIN
;**********************************************************************
BEGIN
;INIT GPIO
MOVLW ~(1<<2) ;GP2 IS OUTPUT
BANKSEL TRISIO
MOVWF TRISIO
;CONFIGURE COMPARATOR
MOVLW 0<<CINV|b'001'
;SELECT MODE 1 (CM=001)
; +REF IS CIN+, -REF IS CIN-,
; COMPARATOR ON, EXTERNAL OUTPUT IS GP2
;OUTPUT NOT INVERTED (CINV=0)
; -> COUT=1 IF CIN+ > CIN-
BANKSEL CMCON
MOVWF CMCON
MAINLOOP
GOTO MAINLOOP
END1) MOVLW ~(1<<2) ;GP2 IS OUTPUT (instead of MOVLW ~(1<<5))
2) MOVLW 0<<CINV|b'001' (instead of MOVLW 0<<CINV|b'010')
3) The MAINLOOP is empty.
In this code, the main loop is empty because supposedly, the output comparator is directly connected to GP2, which is where I put the LED now. However, no matter how much I turn the potentiometer, the LED is always on. What am I doing wrong?
