;--------------------------------------------------------------------------------------------
; FILE: Flashing LED  -  20MHz Clock 
; AUTH: Ed's Projects
; DATE: 20/06/2016
; DESC: When a button is held down on Pin 1 (RA1) an LED will flash on pin 10 (RB4) until released.
;--------------------------------------------------------------------------------------------

	LIST      	P=16F628A, R=DEC	; All numbers Decimal format unless otherwise stated.
	include		<P16F628A.inc>		; Define configurations, registers, etc.
	__config 	_CP_OFF & _CPD_OFF & _LVP_OFF & _BOREN_ON & _MCLRE_OFF & _PWRTE_ON & _WDTE_OFF & _HS_OSC
	
;	_LP_OSC			; Low power crystal - 32kHz - 200kHz
;	_XT_OSC			; Crystal / resonator - 100kHz - 4MHz
;	_HS_OSC			; High speed crystal - 8MHz - 20MHz
;	_RC_OSC			; External RC oscillator
;	_RC_OSC_NOCLKOUT	; External RC oscillator without clockout pin, allows RA6 to be used as an I/O
;	_INTOSC			; Internal oscillator - 4MHz
;	_INTOSC_OSC_NOCLKOUT	; Internal oscillator - 4MHz without clockout pin
;	_EC_OSC			; External clock
	
;--------------------------------------------------------------------------------------------
;-------------------------------------  Port Definitions  -----------------------------------
;--------------------------------------------------------------------------------------------

; PortA - RA2 - Pin 1 - Input button
;
; PortB - RB4 - Pin 10 - Output for LED	

;--------------------------------------------------------------------------------------------
;---------------------------------------  Variables  ----------------------------------------
;--------------------------------------------------------------------------------------------
				cblock	h'20'	    ; 1st part of General Purpose Register I can use.

delay1						    ; Variable 1
delay2						    ; Variable 2

				endc
;--------------------------------------------------------------------------------------------
;-------------------------------------  Program Code  ---------------------------------------
;--------------------------------------------------------------------------------------------

                ORG     0               ; Start assembly here Reset vector. 
.
;--------------------------------------------------------------------------------------------
;--------------  Initialisation  - Set up all ports. Make unused ports outputs.  ------------
;--------------------------------------------------------------------------------------------
Init	    bsf	    STATUS,RP0		; Set RP0 to 1
	    bcf	    STATUS,RP1		; Set RP1 to 0
					; Bank 1 Selected
					
	    clrf    VRCON		; Set Vref to off
	    clrf    TRISB		; Set all PortB as Output

	    movlw   b'00000100'		; Load 00000100 to working register
	    movwf   TRISA		; Set bit 2 as input on PortA

	    bcf	    STATUS,RP0		; Set RP0 to 0
					; Bank 0 Selected
					
	    movlw   d'7'		; Load working register with "7"
	    movwf   CMCON		; Turn off comparators
	    
	    clrf    PORTA
	    clrf    PORTB
	    clrf    delay1
	    clrf    delay2		; Clear variables and output ports
	    

;--------------------------------------------------------------------------------------------
;--------------------------------  Main part of program  ------------------------------------
;--------------------------------------------------------------------------------------------
	    
Start 			
	    
	    btfss	    PORTA,2	; Test bit PortA 2, skip if set
	    goto Start			; Loop back to start
						
label_1						
	    movlw	    b'00010000'	; Load working register with 00010000
	    movwf	    PORTB	; Move working register contents to PortB
	    call	    pause200ms	; call subroutine "pause200ms"
	    clrf	    PORTB	; Clear contents PortB, all pins low
	    call	    pause200ms	; call subroutine "pause200ms"
	    goto	    Start	; Loop back to start
	    
	    
	    
pause200ms	    
	    movlw	    d'199'	; load working register with "199"
	    movwf	    delay1	; move working register to variable "delay1"
delay_1b	    
	    movlw	    d'200'	; load woring register with "200"
	    movwf	    delay2	; move working register to variable "delay2"
delay_1a	
	    nop				; No operation - waste time - 1us
	    nop				; No operation - waste time - 1us
	    decfsz	    delay2,f	; Decrement value of variable "delay2" by 1, skip next instruction when zero
	    goto	    delay_1a	; Loop to label delay_1a
					
delay_1c	
	    decfsz	    delay1,f	; Decrement value of variable "delay1" by 1, skip next instruction when zero
	    goto	    delay_1b	; Loop to label delay_1b
					; total of 200ms
	    return			; Return subroutine call
	    
	    
	    
	    END				;Stop assembling here
;--------------------------------------------------------------------------------------------