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Information in this article applies to:

  • MCB520 Evaluation Boards
  • C51 Version 5.50


I am using the MCB520 board and I would like to know if the Monitor is using the 520 device with four oscillator cycles per machine cycle or 12 oscillator cycles per machine cycle. If it is 12 then is it possible to obtain a version of the monitor that uses the faster speed?


By default the Dallas 520 device powers up in the four oscillator cycles per machine cycle state (refer to the default settings for CD0 and CD1 in the PMR Power Management Register) and it is this state that the monitor uses.

Note that the timers may be individually configured to use the faster or slower state. The default is the slower state in order to make them compatible with 'standard' 8051s.


  • Refer to the Dallas Semiconductor High-Speed Microcontroller Data Book for full details of the 520 and family members.
  • For more information about the MCB520 evaluation board, refer to the following URL:

Last Reviewed: Tuesday, July 19, 2005

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