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I want to use a PIC16F877A (I have a boot loader on it) to control the speed of an electric motor. I also want to use the PIC for a few other things not related to this problem so I want to program it in assembly for better programming control (and for the fun of it). Motor speed will be controlled using a potentiometer as input in a voltage divider. The voltage will be measured using one of the analog pins on the PIC (I don't care which one). The measured voltage will used to set the value of a PWM signal that will go to an H-bridge.

My circuit is pretty much already built but I've lost my notes from mechatronics class years ago. How can I program the PIC16F877A in assembly code to measure voltage at one of the analog pins and output a PWM signal to an H-bridge?

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Do I need to reply to my own post? I wrote some of the A2D but I'm not sure if it's correct because I don't have any way to output the result (like PWM and motor speed).

In this code, I want to use RA0/AN0 as the A2D pin. After this, I'm stuck.

LIST P=16F877A
INCLUDE P16F877.INC

org 0x1F00 ; For the boot loader
goto Start

Start
; 01 = B1
bsf STATUS, RP0
bcf STATUS, RP1

; Set PORTA to output
MOVLW B'11111111'
MOVWF TRISA

; Set PORTE to output
MOVLW B'11111111'
MOVWF TRISE

; Justify left the A2D inputs
; All possible pins are analog, VREF+ = VDD, VREF- = VSS
clrf ADCON1

; 00 = B0
bcf STATUS, RP0

; Fosc / 8, RA0/AN0, AD on
movlw B'01000001'
movwf ADCON0

; Get the AD measurement
GetAD
bsf ADCON0, GO
Pause
btfsc ADCON0, GO
goto Pause
return

Main
call GetAD ; Get the AD measurement
goto Main ; Loop back
END

Member Avatar for 3ak

I revised my previous code and added the PWM from what I read about it. Can someone please help?

LIST P=16F877A
INCLUDE P16F877.INC

org 0x1F00 ; For the boot loader
__CONFIG _WDT_OFF

Start
; 01 = B1
bsf STATUS, RP0
bcf STATUS, RP1

; Set PORTA to input
movlw B'11111111'
movwf TRISA

; Set PORTE to input
movlw B'11111111'
movwf TRISE

; Justify left the A2D inputs
; All possible pins are analog, VREF+ = VDD, VREF- = VSS
clrf ADCON1

; 00 = B0
bcf STATUS, RP0

; Fosc / 8, RA0/AN0, AD on
movlw B'01000001'
movwf ADCON0

; 00 = not used, 11 = LSB, 1100 = PWM
movlw B'00111100'
movwf CCP1CON

goto Main
; call GetAD

; Move the new values from the A2D, ADRESH and ADRESL,
; to the PWM values, CCPR1H and CCPR1L, respectively
SetPWM
movf ADRESH, CCPR1H
movf ADRESL, CCPR1L
return

; Get the AD measurement
GetAD
bsf ADCON0, GO
Pause
btfsc ADCON0, GO
goto Pause
return

Main
call GetAD ; Get the AD measurement
call SetPWM ; Set the PWM values
goto Main ; Loop back

end

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