pic18f assembly example 1 – digital output controlled by digital input

;-----------------------------------------------------------------------------------------------------------------------------
; This assembly code monitors RD4 (pin 27)  on the pic18f4620. If RD4 is high LATD2 (pin 21) is set high otherwise LATD2 is set low
;
; by David Dorran (https://dadorran.wordpress.com) May 2014
;-----------------------------------------------------------------------------------------------------------------------------

; TRY TO DO THE FOLLOWING IN ORDER TO DEVELOP YOUR PROGRAMMING SKILLS:
;    1. change the digital input monitored to RD3
;    2. Set LATD2 high if both RD3 and RD4 are high


;configure the  assembler directive 'list' so as to set processor to 18f4620 and set the radix used for data expressions to decimal (can be HEX|DEC|OCT)
    list p=18f4620, r=DEC
    #include <p18f4620.inc>
; configure the micro so that the watchdog timer is off, low-voltage programming is off, master clear is off and the clock works off the internal oscillator
    config WDT=OFF, LVP=OFF, MCLRE=OFF, OSC=INTIO67
;The org directive tells the compiler where to position the code in memory
    org 0x0000 ;The following code will be programmed in reset address location i.e. This is where the micro jumps to on reset
    goto Main ;Jump to Main immediately after a reset
 
 ;NOTE: When an interrupt is triggered the micro jumps to 0x0008 for high priority and 0x0018 for low priority. For this reason you 
 ;don't want to place any 'code' at these locations and this is why the you just jump to somewhere else in memory after a reset. 
 ;If interrupts aren't used then there's no problem just moving the Main code to address 0x0000
 

;--------------------------------------------------------------------------
; Main Program
;--------------------------------------------------------------------------
    org 0x0020 ;The main code section will be programmed starting from address 20H.
Main
    ; configure D0-D3 as outputs and D4-D7 as inputs by modifying the TRISD register
    movlw 0xf0
    movwf TRISD 
    CLRF LATD ; turn off all the outputs
    
main_loop
    BTFSS PORTD,4 ; if RD4 is set skip the next line
    goto turn_LATD2_off
        
    bsf LATD,2 ; turn on LATD2 - we wont reach this line in loop if RD4 is low
    goto main_loop
    
turn_LATD2_off   
    bcf LATD,2 ; turn on LATD2        
    goto main_loop   

    END