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machine cycle for an instruction

Discussion in 'Assembly Language Programming (ALP) Forum' started by swaeded, May 8, 2007.

  1. swaeded

    swaeded New Member

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    Hi,

    In 8085 instruction,
    1 byte instruction takes 1 machine cycle and 4 t-states.
    2 byte instruction takes 2 machine cycle and 4+3 t-states.
    3 byte instruction takes 4 machine cycle and 4+3+3+3 t-states.

    then y out and in instruction which is a 2-byte instruction takes 3- machine cycles....
     
  2. DaWei

    DaWei New Member

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    I can only suggest that you review the logic schematic of the 8085, bearing in mind setup and hold times and prop delays.
     
  3. vishant103

    vishant103 New Member

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    hello sir can u help me how to count machine cycle?
     
  4. xpi0t0s

    xpi0t0s Mentor

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    Because your initial assumptions are wrong:
    This may be the *general* rule but it doesn't apply to all instructions. A quick google found http://www.google.co.uk/url?sa=t&so..._OSwCA&usg=AFQjCNHOmwV0pomUKU8SI5LB2jCA_ZLjXQ

    haha, nasty URL, and it's a PDF, but it lists ADC M as 1 byte and 2 M-cycles (1/2), CALL 3/5, CC is 3/2 if the transfer is not taken but 3/5 if it is, and so on. So it is clear that not all instructions follow your 1/1; 2/2; 3/4 assumption.

    So read the documentation in detail and do not assume any generalisation holds for *all* possibilities; this is rarely the case.
     

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