EEPW论坛

  测试程序如下：

  mov.b #2eh,hr1       ;<10MHz
  mov.b #01h,hr0       ;enable high-speed on-chip oscillator
  nop                            ;wait for oscillator stable
  nop
  nop
  nop
  mov.b #03h,hr0       ;select high-speed on-chip oscillator
  mov.b #10h,cm1     ;low-speed on-chip oscillator off
                                     ;set cpu clock as Fosc
                                     ;set P4_6,P4_7 as input and low drive capacity
  mov.b #2ch,cm0     ;no external clock
                                     ;stop peripheral funtion clock in wait mode
  mov.b #0ch,ocd      ;disable oscillation stop detection.Confirmed:disable
                                     ;main oscillor stopped
                                     ;select internal oscillor

;下面的为循环，测试周期
loop:
  mov.b 501h,503h              ;3个指令周期 X 10行
  mov.b 501h,503h
  mov.b 501h,503h
  mov.b 501h,503h
  mov.b 501h,503h
  mov.b 501h,503h
  mov.b 501h,503h
  mov.b 501h,503h
  mov.b 501h,503h
  mov.b 501h,503h
  bnot p04                       ;取反P04口，用示波器观察周期，3个指令周期
  jmp.b loop                   ;4个指令周期

理论计算高/低电平的时间应当小于4us，实际测量居然近13us，为什么？？？