Hi, I am an engineering student. Please help me to understand this program. Can anyone help me by adding relevant comments to each lines of the program?

#INCLUDE<P16F88.INC> ; PIC definitions

SET_UPPER	EQU	0x20
SET_LOWER	EQU	0x21
READ_UPPER	EQU	0x22
READ_LOWER	EQU	0x23
P_gain		EQU	0x24
I_gain		EQU	0x25
D_gain		EQU	0x26
Prop		EQU	0x27
Int     	EQU 0x28
Diff		EQU	0x29
DError		EQU	0x30
IError		EQU	0x31
temp		EQU	0x32
	
	ORG 0h
;****************************
;		INITIZLIZATION
;****************************
	
	BANKSEL	TRISA			;SELECT TRISA BANL
	MOVLW	B'00000011'		;MAKE PIN0  AND 1 INPUT
	MOVWF	TRISA           ;
	BANKSEL	ANSEL
	MOVLW	B'00000011'		;MAKE PA0 AND PA1 ANALOG INPUT
	MOVWF	ANSEL
	BANKSEL	PORTA
	MOVLW	0x80			;FOSC/32 AND CHANNEL0
	MOVWF	ADCON0
	MOVLW	0x00
	CLRF	ADCON1			;LEFT JUSTIFIED ADC VALUE
	CLRF	CCP1CON			;PWM MODULE
	CLRF	TRISB			;MAKE PORT B O/P FOR PWM
	MOVLW	0xFF
	MOVWF	PR2
	CLRF	CCPR1L			;0 DUTY CYCLE AT START
	MOVLW	0x01
	MOVWF	T2CON			;PRESCALER 4 AND POSTSCALAR 1
	BSF		T2CON,TMR2ON	;SWITCH ON TIMER
;****************************
;		    MAIN
;****************************
MAIN
	CALL 	SET_POINT		;READ SET POINT
	CALL	READ_TEMP		;READ TEMPERTAURE
	CALL	COMPARE			;COMPARE AND FIND GAIN VALUE
	CALL	CONTROL			;MAP GAIN TO DUTY CYCLE
	GOTO 	MAIN

;****************************
;		READ SET PT.
;****************************
SET_POINT
	MOVLW	0x80
	MOVWF	ADCON0			;CHANNEL 0 ADC
	BSF		ADCON0,ADON		;SWITCH ON ADC
	NOP						;WAIT ACQUISITION TIME
	NOP
	NOP
	NOP
	NOP
	BSF 	ADCON0,GO
ADC	
	BTFSC	ADCON0,GO		;WAIT TILL CONVERSION IS COMPLETE
	GOTO	ADC
	MOVF	ADRESH,W		;READ ADC VALUES
	MOVWF	SET_UPPER
	BANKSEL	ADRESL
	MOVF	ADRESL,W
	MOVWF	SET_LOWER
	BANKSEL	PORTA
	RETURN
;****************************
;	   READ TEMPERATURE
;****************************
READ_TEMP
	MOVLW	0x88			;ADC CHANNEL 1 SELECT
	MOVWF	ADCON0
	BSF		ADCON0,ADON		;SWITCH ON ADC
	NOP						;WAIT ACQUSITION TIME
	NOP
	NOP
	NOP
	NOP
	BSF 	ADCON0,GO		;START CONVERSION
ADC0	
	BTFSC	ADCON0,GO		;WAIT TILL CONVERSION IS COMPLETE
	GOTO	ADC0
	MOVF	ADRESH,W
	MOVWF	READ_UPPER		;READ ADC VALUE
	BANKSEL	ADRESL
	MOVF	ADRESL,W
	MOVWF	READ_LOWER
	BANKSEL PORTA
	RETURN
;******************************
;   COMPUTE ERROR AND GAINS
;******************************
COMPARE
	MOVF	SET_UPPER,W
	SUBWF	READ_UPPER,W	;SUBTRACT READ VALUE FROM SET POINT
	SUBWF	DError,F		;COMPUTE INTEGRAL ERROR
	ADDWF	IError,F		;COMPUTE DIFFERENTIAL ERROR
	
	MOVWF	Prop			;MOVE COMPUTED ERROR TO PROP
	MOVF	P_gain,W		
	MOVWF	temp
	MOVF	Prop,W			
Prop_loop
	ADDWF	Prop,F			;ADD PRPORTIONAL ERROR PROPORTIONAL GAIN TIMES
	DECFSZ	temp,F
	GOTO	Prop_loop
	
	MOVF	IError,W
	MOVWF	Int
	MOVF	I_gain,W
	MOVWF	temp
	MOVF	Int,W	
Int_loop
	ADDWF	Int,F			;ADD INTEGRAL ERROR INTEGRAL GAIN TIMES
	DECFSZ	temp,F
	GOTO	Int_loop

	MOVF	DError,W
	MOVWF	Diff
	MOVF	D_gain,W
	MOVWF	temp
	MOVF	Diff,W	
Diff_loop
	ADDWF	Diff,F			;ADD DIFFERENTIAL ERROR DIFFERENTIAL GAIN TIMES
	DECFSZ	temp,F
	GOTO	Diff_loop
	RETURN
;***************************
;	MAP GAIN TO PWM VALUE
;***************************
CONTROL
	MOVF	Prop,W			;ADD ALL THREE COMPUTED VALUES
	ADDWF	Int,W
	ADDWF	Diff,W
	MOVWF	CCPR1L			;MOVE TO CCPR1L TO MAKE IT HI TIME OF PWM
	RETURN
	
	END

 

It's already well commented, I suggest downloading the PIC16F88 datasheet from microchip.com and reading through the "instruction set summary" section.

 

It's already well commented, I suggest downloading the PIC16F88 datasheet from microchip.com and reading through the "instruction set summary" section.

Hello Markd77, Please help me to add comments. Its really urgent. Some of the instructions could not be found:

"BANKSEL ANSEL" etc

Please. please .please help me..

 

Banksel is a compiler directive that generates a couple of lines of assembler to change the RP0 and RP1 bits of STATUS so that the bank that ANSEL is in is selected.
ANSEL is the register that controls most of the analog settings.
See section 2.2 and 12 of the datasheet.