; Registers:
; B: minutes
; C: hours
; E: seconds
; D: flags

BLINK_ON_BIT	EQU		0
BLINK_ALL_BIT	EQU		1
PM_BIT		EQU		2
MIN_BUTTON_BIT	EQU		3
HOUR_BUTTON_BIT	EQU		4

TIMER_0		EQU		08h
TIMER_1		EQU		09h
TIMER_2		EQU		0Ah
TIMER_CNTRL	EQU		0Bh

DISPLAY		EQU		00h
BUTTONS		EQU		04h
DISP_ON		EQU		0Dh
DISP_OFF	EQU		0Ch
RESET_DISP	EQU		0Ah
INC_DISP	EQU		08h
DEC_DISP	EQU		09h
BLANK_ZERO	EQU		0Eh
SHOW_ZERO	EQU		0Fh
LAMP_TEST	EQU		0Bh

AM_COLON_ON	EQU		04h	
AM_COLON_OFF	EQU		01h
PM_COLON_ON	EQU		08h
PM_COLON_OFF	EQU		07h

COLON_AM_PM	EQU		00h
MINUTE_LOW	EQU		01h
MINUTE_HIGH	EQU		02h
HOUR_LOW	EQU		03h
HOUR_HIGH	EQU		04h

SET_BUTTON	EQU		0
MIN_BUTTON	EQU		1
HOUR_BUTTON	EQU		2

NUM_SECONDS	EQU		60

		ORG		0

		DI
		JP		INIT

; interrupt handler

		ORG		38h
		DI

; check for button press

		IN		A, (BUTTONS)
		BIT		SET_BUTTON, A
		JP		Z, BUTTON_HANDLER
		RES		MIN_BUTTON_BIT, D
		RES		HOUR_BUTTON_BIT, D

; update time	

; update minutes	

		DEC		E
		JP		NZ, BLINK
		LD		E, 2*NUM_SECONDS
		INC		B
		LD		A, B
		AND		A, 0Fh
		CP		0Ah
		JP		NZ, REFRESH_MIN
		LD		A, B
		AND		A, F0h
		ADD		A, 10h
		LD		B, A
		CP		60h
		JP		NZ, REFRESH_MIN
		LD		B, 00h

; update hours

		INC		C
		LD		A, C
		CP		0Ah
		JP		Z, SET_TO_TEN
		CP		13h
		JP		Z, SET_TO_ONE
		CP		12h
		JP		Z, UPDATE_AM_PM
		JP		REFRESH_HOUR
SET_TO_TEN:	LD		C, 10h
		JP		REFRESH_HOUR
SET_TO_ONE:	LD		C, 01h
		JP		REFRESH_HOUR		

; reverse pm bit

UPDATE_AM_PM:	BIT		PM_BIT, D
		JP		NZ, SET_AM
		SET		PM_BIT, D
		BIT		BLINK_ALL_BIT, D
		JP		Z, REFRESH_HOUR
		LD		A, COLON_AM_PM
		OUT		(DISPLAY), A
		NOP
		NOP
		NOP
		NOP
		LD		A, PM_COLON_ON
		OUT		(DISPLAY), A
		NOP
		NOP
		NOP
		NOP
		JP		REFRESH_HOUR
SET_AM:		RES		PM_BIT, D
		BIT		BLINK_ALL_BIT, D
		JP		Z, REFRESH_HOUR
		LD		A, COLON_AM_PM
		OUT		(DISPLAY), A
		NOP
		NOP
		NOP
		NOP
		LD		A, AM_COLON_ON
		OUT		(DISPLAY), A
		NOP
		NOP
		NOP
		NOP
		JP		REFRESH_HOUR


REFRESH_MIN:	LD		A, MINUTE_LOW
		OUT		(DISPLAY), A
		NOP
		NOP
		NOP
		NOP
		LD		A, B
		OUT		(DISPLAY), A
		NOP
		NOP
		NOP
		NOP
		LD		A, MINUTE_HIGH
		OUT		(DISPLAY), A
		LD		A, B
		SRA		A
		SRL		A
		SRL		A
		SRL		A
		NOP
		NOP
		NOP
		OUT		(DISPLAY), A
		NOP
		NOP
		NOP
		NOP
		JP		BLINK

REFRESH_HOUR:	LD		A, HOUR_LOW
		OUT		(DISPLAY), A
		NOP
		NOP
		NOP
		NOP
		LD		A, C
		OUT		(DISPLAY), A
		NOP
		NOP
		NOP
		NOP
		LD		A, HOUR_HIGH
		OUT		(DISPLAY), A
		LD		A, C
		SRA		A
		SRL		A
		SRL		A
		SRL		A
		NOP
		NOP
		NOP
		OUT		(DISPLAY), A
		NOP
		NOP
		NOP
		NOP
		JP		REFRESH_MIN


; handle blinking

BLINK:		BIT		BLINK_ALL_BIT, D
		JP		NZ, BLINK_ALL
		BIT		BLINK_ON_BIT, D
		JP		NZ, BLINK_OFF
BLINK_ON:	SET		BLINK_ON_BIT, D
		LD		A, COLON_AM_PM
		OUT		(DISPLAY), A
		LD		A, AM_COLON_ON
		BIT		PM_BIT, D
		JP		Z, AM_ON
		LD		A, PM_COLON_ON
AM_ON:		NOP
		NOP
		NOP
		NOP
		OUT		(DISPLAY), A
		NOP
		NOP
		NOP
		NOP
		JP		EOI
BLINK_OFF:	RES		BLINK_ON_BIT, D
		LD		A, COLON_AM_PM
		OUT		(DISPLAY), A
		LD		A, AM_COLON_OFF
		BIT		PM_BIT, D
		JP		Z, AM_OFF
		LD		A, PM_COLON_OFF
AM_OFF:		NOP
		NOP
		NOP
		NOP
		OUT		(DISPLAY), A
		NOP
		NOP
		NOP
		NOP
		JP		EOI
BLINK_ALL:	BIT		BLINK_ON_BIT, D
		JP		NZ, BLINK_ALL_OFF
		SET		BLINK_ON_BIT, D
		LD		A, DISP_ON
		OUT 		(DISPLAY), A
		NOP
		NOP
		NOP
		NOP
		JP		EOI
BLINK_ALL_OFF:	RES		BLINK_ON_BIT, D
		LD		A, DISP_OFF
		OUT		(DISPLAY), A
		NOP
		NOP
		NOP
		NOP
		JP		EOI

; end of interrupt

EOI:		EI
		HALT

BUTTON_HANDLER: BIT		BLINK_ON_BIT, D
		JP		NZ, ALREADY_ON
		BIT		BLINK_ALL_BIT, D
		JP		NZ, ON_FROM_OFF
		LD		A, COLON_AM_PM
		OUT		(DISPLAY), A
		NOP
		NOP
		NOP
		LD		A, AM_COLON_ON
		BIT		PM_BIT, D
		JP		Z, ON_FROM_AM
		LD		A, PM_COLON_ON
ON_FROM_AM:	OUT		(DISPLAY), A
		NOP
		NOP
		NOP
		JP		ALREADY_ON
ON_FROM_OFF:	SET		BLINK_ALL_BIT, D
		LD		A, DISP_ON
		OUT		(DISPLAY), A
		NOP
		NOP
		NOP
ALREADY_ON:	RES		BLINK_ALL_BIT, D
		SET		BLINK_ON_BIT, D
		LD		E, 2*NUM_SECONDS
		IN		A, (BUTTONS)
		BIT		MIN_BUTTON, A
		JP		Z, SET_MIN
		BIT		HOUR_BUTTON, A
		JP		Z, SET_HOUR
		RES		MIN_BUTTON_BIT, D
		RES		HOUR_BUTTON_BIT, D
		JP		EOI

SET_MIN:	RES		HOUR_BUTTON_BIT, D
		INC		B
		LD		A, B
		AND		A, 0Fh
		CP		0Ah
		JP		NZ, MIN_OK
		LD		A, B
		AND		A, F0h
		ADD		A, 10h
		LD		B, A
		CP		60h
		JP		NZ, MIN_OK
		LD		B, 00h
MIN_OK:		LD		A, MINUTE_LOW
		OUT		(DISPLAY), A
		NOP
		NOP
		NOP
		NOP
		LD		A, B
		OUT		(DISPLAY), A
		NOP
		NOP
		NOP
		NOP
		LD		A, MINUTE_HIGH
		OUT		(DISPLAY), A
		LD		A, B
		SRA		A
		SRL		A
		SRL		A
		SRL		A
		NOP
		NOP
		NOP
		OUT		(DISPLAY), A
		NOP
		NOP
		NOP
		NOP
		LD		H, 1Fh
		BIT		MIN_BUTTON_BIT, D
		JP		NZ, SET_MIN_LOOP1
		LD		H, 7Fh
		SET		MIN_BUTTON_BIT, D
SET_MIN_LOOP1:	LD		A, FFh
SET_MIN_LOOP2:	DEC		A
		JP		NZ, SET_MIN_LOOP2
		IN		A, (BUTTONS)
		BIT		MIN_BUTTON, A
		JP		Z, MIN_DOWN
		RES		MIN_BUTTON_BIT, D
		JP		EOI
MIN_DOWN:	DEC		H
		JP		NZ, SET_MIN_LOOP1
		JP		EOI


SET_HOUR:	INC		C
		LD		A, C
		CP		0Ah
		JP		Z, HBTN_SET_TEN
		CP		12h
		JP		Z, HBTN_SET_AM_PM
		CP		13h
		JP		NZ, HOUR_OK
		LD		C, 01h
		JP		HOUR_OK
HBTN_SET_TEN:	LD		C, 10h
		JP		HOUR_OK		
HBTN_SET_AM_PM:	BIT		PM_BIT, D
		JP		Z, HBTN_PM_ON
		RES		PM_BIT, D
		LD		A, COLON_AM_PM
		OUT		(DISPLAY), A
		NOP
		NOP
		NOP
		NOP
		LD		A, AM_COLON_ON
		OUT		(DISPLAY), A
		NOP
		NOP
		NOP
		NOP
		JP		HOUR_OK
HBTN_PM_ON:	SET		PM_BIT, D
		LD		A, COLON_AM_PM
		OUT		(DISPLAY), A
		NOP
		NOP
		NOP
		NOP
		LD		A, PM_COLON_ON
		OUT		(DISPLAY), A
		NOP
		NOP
		NOP
		NOP
HOUR_OK:	LD		A, HOUR_LOW
		OUT		(DISPLAY), A
		NOP
		NOP
		NOP
		NOP
		LD		A, C
		OUT		(DISPLAY), A
		NOP
		NOP
		NOP
		NOP
		LD		A, HOUR_HIGH
		OUT		(DISPLAY), A
		LD		A, C
		SRA		A
		SRL		A
		SRL		A
		SRL		A
		NOP
		NOP
		NOP
		OUT		(DISPLAY), A
		NOP
		NOP
		NOP
		NOP
		LD		H, 1Fh
		BIT		HOUR_BUTTON_BIT, D
		JP		NZ, SET_HOUR_LOOP1
		LD		H, 7Fh
		SET		HOUR_BUTTON_BIT, D
SET_HOUR_LOOP1:	LD		A, FFh
SET_HOUR_LOOP2:	DEC		A
		JP		NZ, SET_HOUR_LOOP2
		IN		A, (BUTTONS)
		BIT		HOUR_BUTTON, A
		JP		Z, HOUR_DOWN
		RES		HOUR_BUTTON_BIT, D
		JP		EOI
HOUR_DOWN:	DEC		H
		JP		NZ, SET_HOUR_LOOP1
		JP		EOI

; initialization

INIT:		LD		B, 00h
		LD		C, 12h
		LD		D, 00h
		LD		E, 2*NUM_SECONDS
		;SET		BLINK_ON_BIT, D
		SET		BLINK_ALL_BIT, D

; program counter 0 for mode 2

		LD		A, 34h
		OUT		(TIMER_CNTRL), A

; load count (divide by 8 = 0008h)

		LD		A, 08h
		OUT		(TIMER_0), A
		LD		A, 00h
		OUT		(TIMER_0), A

; program counter 1 for mode 2

		LD		A, 74h
		OUT		(TIMER_CNTRL), A

; load count (divide by 62500 = F424h)

		LD		A, 24h
		OUT		(TIMER_1), A
		LD		A, F4h
		OUT		(TIMER_1), A

; program counter 2 for mode 5

		LD		A, BAh
		OUT		(TIMER_CNTRL), A

; load count 96h = 1200 microsecond delay)

		LD		A, 96h
		OUT		(TIMER_2), A
		LD		A, 00h
		OUT		(TIMER_2), A

; initialize display

		LD		A, RESET_DISP
		OUT		(DISPLAY), A
		NOP
		NOP
		NOP
		LD		A, DISP_OFF
		OUT		(DISPLAY), A
		NOP
		NOP
		NOP
		LD		A, BLANK_ZERO
		OUT		(DISPLAY), A
		NOP
		NOP
		NOP

; turn on colon and turn off pm light

		LD		A, COLON_AM_PM
		OUT		(DISPLAY), A
		NOP
		NOP
		NOP
		LD		A, AM_COLON_ON
		OUT		(DISPLAY), A
		NOP
		NOP
		NOP

; display first digit

		LD		A, MINUTE_LOW
		OUT		(DISPLAY), A
		NOP
		NOP
		NOP
		LD		A, 00h
		OUT		(DISPLAY), A
		NOP
		NOP
		NOP

; display second digit

		LD		A, MINUTE_HIGH
		OUT		(DISPLAY), A
		NOP
		NOP
		NOP
		LD		A, 00h
		OUT		(DISPLAY), A
		NOP
		NOP
		NOP

; display third digit

		LD		A, HOUR_LOW
		OUT		(DISPLAY), A
		NOP
		NOP
		NOP
		LD		A, 02h
		OUT		(DISPLAY), A
		NOP
		NOP
		NOP

; display last digit

		LD		A, HOUR_HIGH
		OUT		(DISPLAY), A
		NOP
		NOP
		NOP
		LD		A, 01h
		OUT		(DISPLAY), A
		NOP
		NOP
		NOP

; enable interrupts and halt

		LD		A, DISP_ON
		OUT		(DISPLAY), A
		NOP
		NOP
		NOP
		IM		1
		EI
		HALT

		END