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For my stopwatch I need a precision of a hundredth of a second. By using a 18f252 Timer1 driven by a quartz to 32768 hz, I try to get an interrupt every 10 ms that I should increase a variable, but I can not get the right precision although the use of instant interrupt Darrel Taylor. Could someone give me some hints with timer setting? Thanks
You will need to fine tune the preload value maybe. Do you have an O-scope? How do you know it is not correct? What else does the code do? Did you set your configs correctly? We really will need to know a bit more if we are going to be able to help you. We HAVE NO crystal ball!!
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Keyword : " Elapsed timer " .............................
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Alain
Sorry Alain but I use in my stopwatch a ds32khz chip that drives the Timer1, and a crystal of 4 MHz for the 18f252. I believe that the 'elapsed timer using also a crystal of 4 MHz for the pic and 4 mhz/4 (1 Mhz) for Timer1. Am I wrong? Anyway I attach the listing.
'************************************************* ***************
'* Name : UNTITLED.BAS *
'* Author : [select VIEW...EDITOR OPTIONS] *
'* Notice : Copyright (c) 2011 [select VIEW...EDITOR OPTIONS] *
'* : All Rights Reserved *
'* Date : 26/01/2011 *
'* Version : 1.0 *
'* Notes : *
'* : *
'************************************************* ***************
@ __CONFIG _CONFIG1H,_OSCS_OFF_1H & _HS_OSC_1H
@ __CONFIG _CONFIG2L,_BOR_OFF_2L & _PWRT_ON_2L
@ __CONFIG _CONFIG2H,_WDT_OFF_2H
@ __CONFIG _CONFIG3H,_CCP2MX_OFF_3H
@ __CONFIG _CONFIG4L,_STVR_OFF_4L & _LVP_OFF_4L
'---------------SETTAGGI PORTE ----------------------
INTCON2.7=0 'ABILITA PORTB PULLUP
TRISB =%00000111
PORTB =%00000111
TRISC =%00000001
' --------------SETTAGGI VARI ----------------------------
DEFINE OSC 4 ' Clock a 4 Mhz
DEFINE LCD_BITS 4 'NUMERO LINEE DI COMANDO 4 O 8
DEFINE LCD_DREG PORTB 'PORTA ChE GESTISCE LCD
DEFINE LCD_DBIT 4 'BIT INIZIALE BUS
DEFINE LCD_RSREG PORTC 'PORTA CHE GESTISCE RS
DEFINE LCD_RSBIT 5 'BIT CHE GESTISCE RS
DEFINE LCD_EREG PORTB 'PORTA CHE GESTISCE E
DEFINE LCD_EBIT 3 'PIN CHE GESTISCE IL SEGNALE E
DEFINE LCD_LINES 2 'NUMERO LINEE LCD
Define LCD_COMMANDUS 2000
' Command Delay (uS)
Define LCD_DATAUS 50 ' Data Delay (uS)
CENT VAR BYTE
ORE VAR BYTE
MINS VAR BYTE
SEC VAR BYTE
CENT=0
ORE=0
MINS=0
SEC=0
TIMERUNO VAR WORD
INCLUDE "DT_INTS-18.bas" ' Base Interrupt System
INCLUDE "ReEnterPBP-18.bas" ' Include if using PBP interrupts
ASM
INT_LIST macro ; IntSource, Label, Type, ResetFlag?
INT_Handler TMR1_INT, _ToggleLED1, PBP, yes
endm
INT_CREATE ; Creates the interrupt processor
ENDASM
T1CON=%00000111
START:
IF PORTB.0=1 THEN START
timeruno=65214
TMR1H=TIMERUNO.HIGHBYTE
TMR1L=TIMERUNO.LOWBYTE
high porta.5
pause 10
low porta.5
@ INT_ENABLE TMR1_INT ; enable Timer 1 interrupts
STO:
IF CENT=100 THEN
cent=0
SEC=SEC+1
if sec=60 then
sec=0
mins=mins+1
if mins=60 then
mins=0
ore=ore+1
endif
endif
LCDOUT $FE,$80,DEC2 ore," ",dec2 mins," ",dec2 sec
ENDIF
GOTO STO
'---[INT - interrupt handler]---------------------------------------------------
ToggleLED1:
T1CON.0=0 ' Stop the Clock
TMR1H=TIMERUNO.HIGHBYTE
TMR1L=TIMERUNO.LOWBYTE
T1CON.0=1 ' Restart the Clock
CENT=CENT+1
@ INT_RETURN
Ohhhh
not difficult to use the Low freq osc with a 32768 Hz Xtal ....instead of the Clock Osc : the mod is really easy.
I did it for my lawn tractor computer ...
Alain