;*********************************************************************
;                                                                    *
;     	Tutorial 8 Timer0 Counter Bar-Graph Tacho		     *
;                                                                    *
;*********************************************************************
;*	TARGET PIC16F877
;*********************************************************************
;	Counts the clocks on A4/TOKI in a accumulation period and shows
;	a bar graph value representative of the accumulated count on
;	PortB		
;
;	Expected Result.
;
;	Using a Ramping frequency stimulus file, the bargraph is 
;	expected to start empty and then increment until all elements
;	are lit up before reseting to all clear.
;*********************************************************************
;*
;*	@version 	0.1, 20 September 2001
;*	@author		James Caska
;*********************************************************************


	list      p=16F877                   
	#include <p16F877.inc>               

COUNTER		EQU	.32
TEMP		EQU	.33

	ORG	.0
	GOTO	INIT

;**********************************************************************
;* InterruptVector
;**********************************************************************
;* 	The Interrupt is called on Timer0 overflow
;**********************************************************************
	ORG	.4	
InterruptVector

	MOVLW	.1
	XORWF 	PORTB,F

	MOVLW	.6		;Preload (add) TMR0
	ADDWF	TMR0,F

	BCF	INTCON,T0IF	;Clear Timer0 Interrupt
	RETFIE

LOOKUPBARGRAPH	
	MOVWF	TEMP
	ANDLW	B'11111000'	;If 8 or greater then return maximum bar graph
	BTFSS	STATUS,Z
	RETLW	B'11111111'
	MOVF	TEMP,W
	ADDWF	PCL,F
	RETLW	B'00000000'
	RETLW	B'00000001'
	RETLW	B'00000011'
	RETLW	B'00000111'
	RETLW	B'00001111'
	RETLW	B'00011111'
	RETLW	B'00111111'
	RETLW	B'01111111'
	RETLW	B'11111111'


INIT


	;==========================================
	;Autogenerated configuration code PIC16F877
	;Config Wiz V0.1, www.virtualbreadboard.com
	;==========================================
	;======Begin PORT Configuration
	BSF STATUS, RP0	;PORT TRIS Registers are on page 1
	;======PORT A
	MOVLW   .16	;PORTA Configuration Bits
	MOVWF   TRISA
	;======PORT B
	MOVLW   .0	;PORTB Configuration Bits
	MOVWF   TRISB
	BCF STATUS, RP0	;Restore Page0


	;==========================================
	;Autogenerated configuration code PIC16F877
	;Config Wiz V0.1, www.virtualbreadboard.com
	;==========================================
	;======Begin Timer0 Configuration
	BSF STATUS, RP0	;Timer 0 config register on page 1
	;======Timer0 Counter Mode, uses External clock source
	BSF OPTION_REG,T0CS	;T0CS: TMR0 Clock Source Select bit: 1 = Transition on T0CKI pin
	BCF OPTION_REG,T0SE	;T0SE: TMR0 Source Edge Select bit: 0 = Increment on low-to-high transition on T0CKI pin
	BSF OPTION_REG,PSA	;PSA: Prescaler Assignment bit:1 = Prescaler is assigned to the WDT
	BCF STATUS, RP0	;Restore page 1
	;======Timer0 Interrupt Configuration
	BCF INTCON, T0IE	;Timer 0 InterruptEnableOff
	;======End Timer0 Configuration

	

MAIN
	CLRF	TMR0
	MOVLW	.255
	MOVWF	COUNTER

	;================================
	; Wait for Measurement period [TimeBase]
	;================================
LOOP
	NOP
	NOP
	NOP
	DECFSZ	COUNTER,F
	GOTO	LOOP

	;================================
	; Construct the BarGraph [0..10]
	;================================
	MOVF	TMR0,W
	CALL	LOOKUPBARGRAPH
	MOVWF	PORTB
	
	GOTO	MAIN


	END