.file "tailC.asm"
;; 
;; ATmega8 taillight circuit
;; Last edited:	14-7-2004
;; Purpose:	An assembly language program that generates 5 different
;; static patterns with switching from pattern-to-pattern controlled
;; by the depression of one push-button switch (S2).
;; 
;; A compared C code is followed by "--> " and before the assembly


;; List of all registers are defined in this code
;;------------------------------------------------;;
;; R16 --- PINC
;; R17 --- 0X08 ---> PORTC
;; R18 --- ser 0xFF  -->DDRD
;; R19 --- ADCH & OCR1AL
;; R20 --- ADCH & OCR1AH
;; R21 --- TIFR
;; R22 --- 
;; R23 --- 
;; R24 --- switchNo
;; R25 --- pattern
;; R26 --- 0x00 ---> TCCR1A
;; R27 --- TCCR1B
;; R28 --- bounce0
;; R29 --- bounce1
;; R30 --- S2
;;------------------------------------------------;;

	;; Access the register and register bit definitions
	.include "avr-mega8.asm"

	;; The variable 'pattern' is kept in register 25
	;; Bit set means LED on (complemented before output)
	;; --> unsigned char pattern = 0x00;
	LDI 	R25,0x00  	 	;;Load immediate

	;; The variable 'switchNo' is kept in register 18
	;; --> unsigned int switchNo = 1;
	LDI 	R24,0x01  	 	;;Load immediate

	;; The variable 'switchNo' is kept in register 18
	;; --> unsigned char S2 = 0x08;
	LDI 	R30,0x08  	 	;;Load immediate
	;; --> unsigned char S2Previous;
	LDI 	R28,0x08  	 	;;Load immediate
	
	;; Set up timer 1A control registers
	;; --> TCCR1A = 0;
	LDI 	R26,0x00  	 	;;Load immediate
	OUT 	TCCR1A,R26 	 	;;Out to I/O location

	;; Set up timer 1B : divide by 64 prescaler using OCR1A
	;; Frequency of operation is about 62.5 kHz
	;; --> TCCR1B = 0x0A;
	LDI 	R27, 0x0B  	 	;;Load immediate
	OUT 	TCCR1B,R27 	 	;;Out to I/O location

	;; Set OCR1A to 0x01
	;; Set a delay time 0.5 ms. It check S2 every 0.5 ms
	;; --> OCR1AH = 0x01 ;
	LDI 	R20,0x01 	 	;;Logical OR with Immediate
	OUT     0x2B,R20 	 	;;Out to I/O location
	;; --> OCR1AL = 0x00 ;
	LDI 	R19,0x00 	 	;;Logical OR with Immediate
	OUT     0x2A,R19 	 	;;Out to I/O location

	;; Set up Port D for output
	;; --> DDRD = 0xFF;
	SER 	R18	  	 		;;Set all Bits in Register
	OUT 	DDRD,R18  	 	;;Out to I/O location

loop:
	;; Update LEDs
	;; --> PORTD = pattern;
	COM     R25				;;One's complement
	OUT 	PORTD,R25 	 	;;Out to I/O location

 	;; Enable PC3 as inputs. (default)
	;; --> DDRC &= ~(1 << PC3);
	CBI 	DDRC,3		 	;;Clear Bit in I/O Register
	
	;; Enable pull-ups for tact switches.
	;; --> PORTC = (1 << PC3);
	LDI 	R17,0x08   	 	;;Load immediate
	OUT 	PORTC,R17 	 	;;Out to I/O location

	;; By the depression of one push-button switch (S2)
	;; to switch 5 different static patterns.
	;; S2 = 0 for S2 pressed; S2 = 1 for S2 unpressed
	;; --> unsigned char S2 = (PINC & (1 << PC3));
	IN   	R16,PINC 	 	;;In from I/O location
	AND 	R16,R17 	 	;;Logical AND
	
	;; By press S2 one time, the patterns changes
	;; --> if (!S2)
	;; --> bounce0 ++;
	;; --> else bounce1 = 1;
	;; -->      bounce0 = 0;
	CPI		R16,0x08   	 	;;Skip if bit in register clear
	BRNE	else_bounce
	LDI		R28,0x00   	 	;;Skip if bit in register clear
	LDI		R29,0x01
	RJMP	end_bounce
else_bounce:
	INC 	R28				;;Logical AND with Immediate
end_bounce:

	;; --> if ((bounce1 == 1)&&(bounce0 == 8))
	;; --> switchNo ++;
	;; --> bounce1 = 0;
	CPI		R29,0x01   	 	;;Skip if bit in register clear
	BRNE	end_check
	CPI		R28,0x08   	 	;;Skip if bit in register clear
	BRNE	end_check
	INC 	R24				;;Logical AND with Immediate
	LDI		R29,0x00
end_check:

	;; When press S2 six times, switch to the first patterns
	;; --> if  (switchNo == 6)
	CPI     R24,0x06   	 	;;Compare with immediate
	BRNE    end_switch_full	;;Branch if not equal
	;; --> switchNo = 1;
	LDI 	R24,0x01 	 	;;Load immediate
end_switch_full:

	;; Form switchNo to decide which pattern will be used in this loop
	;; --> if (switchNo == 1)
	CPI 	R24,0x01 	 	;;Compare with immediate
	BRNE	else1	  	 	;;Branch if not equal
	;; --> pattern = 0x24;
	LDI 	R25,0x24	 	;;Load immediate
	RJMP	end_if	 	 	;;Relative jump
else1:
	;; --> else if (switchNo == 2)
	CPI 	R24,0x02   	 	;;Compare with immediate
	BRNE	else2		 	;;Branch if not equal
	;; --> pattern = 0x66;
	LDI 	R25,0x66	 	;;Load immediate
	RJMP	end_if  	 	;;Relative jump
else2:
	;; --> else if (switchNo == 3)
	CPI 	R24,0x03	 	;;Compare with immediate
	BRNE	else3   	 	;;Branch if not equal
	;; --> pattern = 0x99;
	LDI 	R25,0x99	 	;;Load immediate
	RJMP	end_if  	 	;;Relative jump
else3:
	;; --> else if (switchNo == 4)
	CPI 	R24,0x04	 	;;Compare with immediate
	BRNE	else4   	 	;;Branch if not equal
	;; --> pattern = 0x81;
	LDI 	R25,0x81	 	;;Load immediate
	RJMP	end_if  	 	;;Relative jump
else4:
	;; --> else
	;; --> pattern = 0xFF;
	SER 	R25	  	 		;;Set all Bits in Register
	RJMP	end_if			;;Relative jump
end_if:

checktime:
	;; Test OCF1A flag in TIFR
	;; --> while (!(TIFR & (1 << OCF1A)));
	IN  	R21,TIFR	 	;;In from I/O location
	ANDI	R21,0x10	 	;;Logical AND with Immediate
	BREQ	checktime	 	;;Branch if Equal

	;; OCF1A flag bit is set, so reset it (write 1 to it)
	;; --> TIFR |= (1 << OCF1A);
	ORI 	R21, 0x10 	 	;;Logical OR with Immediate
	OUT 	TIFR, R21 	 	;;Out to I/O location
	;; Continue forever
	RJMP	loop		 	;;Relative jump