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Program shows use of timer 0 as a wait-for timer in Assembler for the AVR Butterfly/Atmega169 to emit a tone on the speaker. (approx 35 bytes)
;--------------------------------------------------;
; WAIT_TIMER.ASM for AVR BUTTERFLY ;
; AUTHOR: DANIEL J. DOREY (RETRODAN AT AVR FREAKS) ;
; CREATED: 20-OCT-09 UPDATED: 20-OCT-09 ;
; ;
; PROGRAM DEMONSTRATES USE OF 8-BIT WAIT-FOR TIMER ;
;--------------------------------------------------;
.INCLUDE "M169DEF.INC" ;(BUTTERFLY DEFINITIONS)
;----------------------------------------;
; FIRST I'LL DEFINE SOME REGISTER TO USE ;
;----------------------------------------;
.DEF A = R16 ;GENERAL PURPOSE ACCUMULATOR
.DEF I = R21 ;INDEXES FOR LOOP CONTROL
.DEF J = R22
.ORG 0000
RJMP ON_RESET ;REBOOT/START-UP VECTOR
;INTO OUR PROGRAM
;-----------------------------------------;
; WE START HERE ON ALL RESEST AND REBOOTS ;
; FIRST WE SETUP A STACK AREA AT HIGH RAM ;
;-----------------------------------------;
START:
ON_RESET:
LDI A,LOW(RAMEND) ;SETUP STACK POINTER
OUT SPL,A ;SO CALLS TO SUBROUTINES
LDI A,HIGH(RAMEND) ;WORK CORRECTLY
OUT SPH,A ;
;--------------;
; MAIN ROUTINE ;
;--------------;
MAIN: SBI DDRB,5 ;SET FOR SPEAKER OUTPUT ON PORT B
LDI A,3 ;SET PRESCALE TO 64,
OUT TCCR0A,A ;~=2,000,000Hz/64/2 ~= 15KHz
MAINL:SBI PORTB,5 ;TURN SPEAKER ON
RCALL WAITER ;WAIT
CBI PORTB,5 ;TURN SPEAKER OFF
RCALL WAITER ;WAIT
RJMP MAINL ;GO ROUND
;-----------------------------;
; WAITS FOR CLOCK TO HIT ZERO ;
;-----------------------------;
WAITER:
WLOOP:IN A,TCNT0 ;READ THE CLOCK
CPI A,0 ;CHECK IF ZERO YET
BRNE WLOOP ;WAIT FOR ZERO
RET
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