microcontroller AT89S52 programing advice

Jul 09, 2006 3 Replies
B

im required to make a digital clock , i made several codes using iteration for delay which give not perfect delay. So i want to have suggestion about how to use timer interrupts to have perfect 1 sec delay each time. ive written code please see am i using interrupts correctly..



#include #include unsigned char LED[10]={0x3F,0x06,0x5B,0x4F,0x66,0x6D,125,0x07,0x7F,111}; unsigned char AMPM[2]={119,115}; long int x,sec=0,min=0,hour=0,lmin=0,hmin=0,c=0;hhour=0,lhour=0,le=0,am=0; sbit a=P3^0; sbit b=P3^1; sbit d=P3^4; sbit e=P3^7; sbit f=P3^6; void init_timer() { ET1=1; TMOD=0x20; TH1=0x6; EA=1; TR1=1; }



timer1() interrupt 3 { hmin=min/10; lmin=min%10; hhour=hour/10; lhour=hour%10; while(c


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G

I take it C is the required language? The timer is a snap in assembler

- less than 10 lines. I'm not a C guy but that interrupt routine looks all wrong to me. Oh well.

GG

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N

Too much in the interrupt. Set a flag or inc a counter in the interrupt. Do the work in main. I assume this is a school project. CPU Xtals are do not have the tolerance to keep time very well. It can be off by several minutes a month.

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A

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Doing devides on a 8051 in an interrupt routine is not a good idea. Using a switch statement in an interrupt routine on a 8051 using many of the 8051 compilers not a good idea. (Switch statement code is not re-entrant, so if you use a switch statement anywhere else you will have very strange bugs)

Do the minimum in the interrupt routine. In stead of doing a divide and a mod, rather have a timer counter that you increment every interrupt. You then increment the "second" interrupt every n number of timer interrupts. something like:

int_counter++; if(int_count>=NUMBER_OF_INTS_PER_SECOND) { int_counter=0; sec_counter++; if(sec_counter>=60) { sec_counter=0; min_counter++; } }

Remember that if you are reading these variables from outside the interrupt routine, they should be volatile.

Regards Anton Erasmus

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