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picmicrochip

Delay Subroutine Time Calculation

How do I calculate the total time consumed by a subroutine in PIC? It is given that the PIC master clock is derived from a 1MHz crystal. Here is the code given:

TEMP   EQU 0x1D

DELAY  MOVLW 0x80
       MOVWF TEMP
       NOP
DELAY1 NOP
       DECFSZ  TEMP,F
       GOTO    DELAY1
       RETURN

I have calculated that there are a total of 518 instruction cycles and the total number of Q-cycles = 2072. How would I go on about if the clock is at 2MHz? Thanks.

Solution

  • For a 8 Bit PIC:

    instruction cycle Time = 4 / fOzs

    1MHz means an instruction cyle of 4us. So your code will execute in 518 x 4us = 2,072ms.

    2MHz means an instruction cycle of 2us. So your code will execute in 518 x 2us = 1,036ms.