Jeff Holtzman's Demotration of how to use Timers from Popular Electronics November 1998 Issue
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; Counter/timer test program for Atmel AVR microcontrollers ; Ingeneering Inc. ; www.ingeninc.com ; Jeff Holtzman ; 3/1/98, 6/1/98 ;Description ;Demonstrates use of sleep mode, interrupts, and precise ;hardware generated time delay. From 11/98 issue of ;Popular Electronics magazine. ;AUTHOR = Jeff Holtzman ;TARGET = AT90S1200 ;REQUIRES = 1200def.in .device AT90S1200 .include "1200def.inc" .def Acc = R16; general purpose accumulator .def DispCnt = R17; display counter .def TickCntLo = R18; tick counter .def TickCntHi = R19; tick counter .equ CLK_DIV = 4; divide timer clock by 256 .equ CNT_LO = 61; provides 1 sec delay @ clk/256 .equ CNT_HI = 0 .cseg ; code begins here .org 0 Reset: rjmp V_Reset ; set up interrupt vectors IRQ: rjmp V_IRQ Timer: rjmp V_Timer Comparator: rjmp V_Comp V_IRQ: ; dummy V_Comp: reti ; dummy V_Reset: ldi DispCnt, 0; reset display counter ldi TickCntLo, CNT_LO; reset tick counter ldi TickCntHi, CNT_HI ldi Acc, 255; set PORT B for output out DDRB, Acc out PortB, Acc ldi Acc, 0 ; set PORT D for input out DDRD, Acc ldi Acc, 0b00100000; set bit 5 to enable sleep mode out MCUCR, Acc ldi Acc, CLK_DIV; set up interrupt clock out TCCR0, Acc ldi Acc, 2 ; enable timer interrupt out TIMSK, Acc ldi Acc, $80; enable global interrupts out SREG, Acc Rst_Loop: sleep ; reset comes here in Acc, PinD; input Port D andi Acc, $7f cpi Acc, 0b01111010; if S0+S2 pressed, brne Rst_Loop; reset display and tick counters ldi TickCntLo, CNT_LO ldi TickCntHi, CNT_HI ori Acc, $80 out PortB, Acc ldi DispCnt, 0 rjmp Rst_Loop V_Timer: ; timer interrupt comes here subi TickCntLo, 1; decrement tick counter sbci TickCntHi, 0 brne Exit cpi TickCntLo, 0 brne Exit ; exit if not = 0 inc DispCnt ; else increment display counter, mov Acc, DispCnt com Acc out PortB, Acc ; display it, ldi TickCntLo, CNT_LO; and reset tick counter ldi TickCntHi, CNT_HI Exit: reti |