; Test of a decimal keyboard
;
; Reads the keyboard on port B and displays the activated key on the LEDs
; in hex format.;
; The decimal keyboard is attached to port B:
;   Bit 6: *=Bit0 7=Bit1 4=Bit2 1=Bit3
;   Bit 5: 0=Bit0 8=Bit1 5=Bit2 2=Bit3
;   Bit 4: #=Bit0 9=Bit1 6=Bit2 3=Bit3
;
; Tests with this program showed that parallel operation of the LEDs and
; of the keyboard on the same port (B) is practically impossible due to
; insufficient driving currents of the port pins. No correct values are read.
;
; 8515-Definitions
.NOLIST
.INCLUDE "C:\avrtools\appnotes\8515def.inc"
.LIST
;
; Registers used
.def	mpko=R15 ; Last keyboard status
.def	mpr=R16 ; Multi-function register
.def	mpk=R25 ; Multi-function register for keyboard-interrupt
;
; RAM-Adresses
.equ	taste=$0060 ; First Ram-adress, here the pressed key will be placed
;
; Reset-/Interrupt vector table, most of the inactive
	rjmp	main
	reti ; Ext Int 0
	reti ; Ext Int 1
	reti ; TC1 Capture
	rjmp	test ; TC1 Compare A
	reti ; Compare B
	reti ; TC1 Overflow
	reti ; TC0 Overflow
	reti ; Serial Transfer Complete
	reti ; Serial Rx Complete
	reti ; Data Register Empty
	reti ; Serial Tx Complete
	reti ; Analog Comparator
; Main program
main:
	ldi	mpr,HIGH(RAMEND) ; Stack Pointer Init for Interrupts
	out	SPH,mpr
	ldi	mpr,LOW(RAMEND)
	out	SPL,mpr
; General control register
	clr	mpr ; no SRAM, no Wait, no Sleep-Mode,
	out	MCUCR,mpr ; Ext.Int not used
; Port B is output und keyboard-Input
	ldi	mpr,0x70 ; all as Output
	out	DDRB,mpr
	ldi	mpr,0x00 ; all lamps on
	out	PORTB,mpr
	sts	Taste,mpr
;
; Timer/Counter 0 init
	ldi	mpr,$00 ; Prescaler = 256
	out	TCCR0,mpr
; Timer 1 init
	ldi	mpr,0b00000000 ; Disable Timer Output and PWM-Mode
	out	TCCR1A,mpr ; in Timer Control Register 1A
	ldi	mpr,0b00001011 ; No input noise canceling, clear counter after
		 ; match, Prescaler = 64 ==> 62500 Hz = 16 µs
	out	TCCR1B,mpr ; in Timer Control Register 1B
	ldi	mpr,HIGH(625) ; Compare-value in Compare-Register A
	out	OCR1AH,mpr ; High Byte first
	ldi	mpr,LOW(625)
	out	OCR1AL,mpr ; Low Byte last
	ldi	mpr,0xFF ; No Interrupt on Compare B
	out	OCR1BH,mpr ; High Byte first
	out	OCR1BL,mpr ; Low Byte last
; Interrupt start
	clr	mpr ; External interrupts disable
	out	GIMSK,mpr ; to General Interrupt mask register
	ldi	mpr,0b01000000 ; Timer 1: Overflow Int Off, Compare A Int on,
	out	TIMSK,mpr ; Compare B Int Off, Input Int Off, Timer 0: Int Off
	sei ; interrupt enable
; Incefinite Loop, all execution is interrupt-driven
loop:
	rjmp	loop
; Interrupt Routine for TC1 Compare Match B
tc1ci:
	in	mpk,SREG ; save Status-Register
	push	mpk
	ldi	mpk,0b11110000 ; Upper Nibble to output, lower to input
	out	DDRB,mpk ; on Port B
	ldi	mpk,0x0F ; Upper Nibble to zero, lower nibble sets Pullup resistors
	out	PORTB,mpk
	in	mpk,PINB ; Read result from keyboard
	cp	mpk,mpko ; Compare with older value
	breq	tc1cir ; ne change: return
	mov	mpko,mpk ; Copy new status to old status
	sts	taste,mpk ; New LED-Status
tc1cir:
	ldi	mpk,0xFF ; Port B to all output
	out	DDRB,mpr
	lds	mpk,taste ; pressed key to LEDs
	out	PORTB,mpk
	pop	mpk ; Return from Interrupt
	out	SREG,mpk ; restore Status-Register
	reti
tc0ci:
	ldi	mpr,0xFF
	out	PORTB,mpr
	reti
tc2ci:
	ldi	mpr,0xAA
	out	PORTB,mpr
	reti
test:
;	LDI	mpk,0x0F
;	OUT	DDRB,mpk
;	LDI	mpk,0xF0
;	OUT	PORTB,mpk
	reti