Timer0
From a newbie to newbies
Every 32nd clock cycle of the Timer0 a shift left through carry on PORTC is executed. The value of the counter is on PORTA. Timer0 is connected to the external 32,768 kHz crystal of the Crumb128 board.
From a newbie to newbies
Every 32nd clock cycle of the Timer0 a shift left through carry on PORTC is executed. The value of the counter is on PORTA. Timer0 is connected to the external 32,768 kHz crystal of the Crumb128 board.
| CODE |
;**************************************************************************** ;File name: Timer0.asm ;Description: Every 32nd clock cycle of the Timer0 shift left through carry ; the one on PORTC. The value of the counter is on PORTA. ; Timer0 is connected to the external 32,768 kHz crystal of the ; Crumb128 board. Connect some LEDs to the ports and you'll see ; it too. ; ;Name: Jan Tomko ;Company: Helmholtz Institute, University Clinic Aachen ; www.hia.rwth-aachen.de ; ;Written in: AVR Studio 4 ;Controller: ATmega128 on the Crumb128 board by www.chip45.com ;**************************************************************************** .include "m128def.inc" ;Includes the Atmega128 definitions file .org 0x0000 ;Places the following code from address 0x0000 ;Ports initialization ldi r16, 0x00 ;r16 = 0x00 out DDRA, r16 ;DDRA = 0x00; Port A is output now out DDRC, r16 ;DDRC = 0x00; Port C is output now out PORTA, r16 ;Port A = 0x00 out PORTC, r16 ;Port C = 0x00 ;Timer0 initialization in r16, SFIOR ;set bit7(Timer/Counter Synchronization Mode) cbr r16, TSM ;in SFIOR to 0 => disabled out SFIOR, r16 ; ldi r16, 0x00 ;r16 = 0000 0000 ldi r17, 0x20 ;r17 = 0x20 = 32 (decimal) out TCNT0, r16 ;clear TCNT0 out OCR0, r17 ;OCR0 = 32 (decimal) out TIFR, r16 ;clear TIFR out TIMSK, r16 ;disable clock compare and overflow interrupts ldi r16, 0x0F ;r16 = 0000 1111 out TCCR0, r16 ;CTC mode, prescaling CLKtos/1024 ldi r16, 0x08 ;set bit3(Asynchronous Timer/Counter) in ASSR to 1 out ASSR, r16 ;external 32.768 kHz clock selected(pins TOSC1 and TOSC2) ldi r17, 0x01 ;r17 = 0x0F ldi r18, 0x02 ;r18 = 0000 0010 ;*** Initialization complete *** Clock_wait: in r16, TCNT0 ;read TCNT0 into r16 out PORTA, r16 ;write TCNT0 to PORTA in r16, TIFR ;r16 = TIFR sbrs r16, OCF0 ;wait until output compare flag is set rjmp Clock_wait ;remote jump to Clock_wait lable out TIFR, r18 ;reset output compare flag rol r17 ;shift left through carry out PORTC, r17 ;write r17 to PORTC rjmp Clock_wait ;remote jump to Clock_wait label |