89c51 max frequency?

Discussion in 'Embedded Systems and Microcontrollers' started by onlyvinod56, Oct 24, 2009.

  1. onlyvinod56

    Thread Starter AAC Fanatic!

    Oct 14, 2008
    hello everyone...

    what will be the maximum pulse frequency i can expect from a 89c51 if it is connected with 12MHz crystal.....

    the job of the micro-controller here is to produce a 1MHz pulse sequence with 50% duty cycle...

    is it possible with this mc and crystal.....i dont have much idea about mc...but iam learning the programming through C.....

    one of my friend said that the maximum frequency with 12Mhz for this application is 300Khz......is it right???
  2. Arm_n_Legs

    AAC Fanatic!

    Mar 7, 2007
    Yes and no. The traditional 8051 running at 12MHz takes 1 us for 1 machine cycle. Using a simple CPL P1.0 instruction will toggle the output to generate your pulse. But this instruction takes 1 us to execute. A cycle of pulse will be generated when the instruction is executed two times, which takes 2us. Therefore, the output will be 500 KHz.

    However, the newer 8051 derivatives run faster than that.