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Zitateinen Preset 2^16us - 20.000us = 45536 = 0xB1EOrichtig ist:
ZitatISR_H:Voila - das geht ganz ohne Vorteiler... fertig! Solls genauer sein, nimm einen 4MHz Quarz.
bcf PIR1,TMR1IF
movlw 0xB1
movwf TMR1H
movlw 0xE0
movwf TMR1L
movlw b'10000000' ;LED ist an bit 7
xorwf PORTA,f ;RA7 toggelt alle 200ms und LED blinkt mt 50Hz
RETFIE FAST
;---T1CON: TIMER1 CONTROL REGISTER DS.94
; external TMR1 oscillator is enabled when T1OSCEN = 1
; and TMR1CS is set to 1 external clock enabled
; the signal goes straight from pin RA5 throug a schmitt-trigger
; to the clock input of TMR1.
;; movlw b'00000000'
movlw b'00001010'
; ....1.. b3/T1OSCEN 0/1 external Tmr1-clock disabled/enabled
; ......1. b1/TMR1CS 0/1 = Internal(external clock (FOSC/4)
; .......0 b0/TMR1ON 0/1 disable/enable TMR1
movwf T1CON
clrf TMR1H ;clear Hi-Byt ;TMR1 is set o 0x0000
clrf TMR1L ;clear Lo-Byte