EMC单片机精确定时问题：

只看该作者 · 2007-6-27 11:39

想得到26us的红外载波周期，但输出的实际周期是24.7us，为何，高手帮忙看看：

TCCVAL    EQU    220    ;256-220 = 36(52-8*2), 26us/at 4MHz/no prescale

SR_TCC:
        disi
        MOV     stack_a,a       ;Save the value of A,
        SWAP    stack_a
        SWAPA   STATUS          ;Save the value of STATUS
        MOV     stack_s,a
        ;----------------------------------------------------------
        mov a,@TCCVAL        ;计数器初值
        mov TCC,a

        LedOn
        LedOff

    TCC_Out:
        ;----------------------------------------------------------
        SWAPA   stack_s         ;Restore the saved value of STATUS
        MOV     STATUS,a
        SWAPA   stack_a         ;Restore the saved value of A
        clr    intf

        reti