Need help understanding the clocking frequency... not a hard question :)

[erospawn]

With the following code, the clocking frequency would be 1Mhz with a 4Mhz clock, correct? If I were using TMR0 with prescaler at 1:2 my oveflow frequency would be 4Khz with a period of 2us?

list P=16f630
#include <p16f630.inc>
__config _INTRC_OSC_NOCLKOUT & _BODEN_OFF & _WDT_OFF & _PWRTE_ON & _MCLRE_ON & _CP_OFF & _CP_OFF

cblock 20h
BH,BL,wait,del_clk1,del_clk2,run,runn,count
endc

RESET_VECTOR CODE 0X000
goto main

main


bsf STATUS,RP0 ;bank 1
call 0x3ff
movwf OSCCAL
movlw 0x00
movwf TRISC ;make all PORTC outputs
movlw 0xfD
movwf TRISA ;make all PORTA inputs
movlw 0x00
movwf OPTION_REG
bcf STATUS,RP0
CLRF TMR0
BCF INTCON,5
movlw 0x07 ;turn off comparitors
movwf CMCON

 

[Diver300]

With OPTION_REG cleared, the prescale is 2, but that makes TMR0 overflow at 512 µs if the oscillator is at 4 MHz. That give an overflow frequency of 1953.125 Hz

 

[upand_at_them]

eros, Keep in mind that the calculation is with a preload of 0. If you preload TMR0 with 131 you'll get your 4KHz frequency (250 µs period).