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Correct resistor for a circuit?

Discussion in 'Circuit Simulation & PCB Design' started by halleffector, May 5, 2016.

  1. granddad

    granddad Active Member

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    Hi Tony... the OP problem has moved on is not about leds or resistors now its about how to get a Z80 to read 65,000 NOP's !
     
  2. Tony Stewart

    Tony Stewart Well-Known Member Most Helpful Member

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    so does that mean LED duty cycle is as low as I thought or do MSB address lines toggle?
     
  3. granddad

    granddad Active Member

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    As far as I can see the 16 address bits are stuck .. possibly all at 1's ...
     
  4. dave

    Dave New Member

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  5. halleffector

    halleffector Member

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    Yes, this is exactly the problem.

    All address lines are set to 1 after a few clock cycles have passed, and remain at 1 indefinitely. There is no counting so the CPU does not increase the program counter.
     
  6. granddad

    granddad Active Member

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    Still here ... I have the Z80 pensioner :) under PIC control, signals more or less as DS ... the Reset ( PIC generated) shows how first instruction fetch is achieved ,(M1 & Read ) the wait (PIC generated ) allows control over memory access. just in the process of designing a better control circuit... ( Bus Pirate is ace )
    Z80 clock at +- 20khz

    HE if your reset switch bounced during or after zero state , or not low for the 3 clocks , then Z80 = unknown state ?

    Z80_START.jpg
     
  7. halleffector

    halleffector Member

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    What is zero state? The state the CPU enters when RESET is held low?

    I think I should start a new thread for this problem, since it has moved away a lot from the original question the thread states.
     
  8. granddad

    granddad Active Member

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    HE , Agree , new thread. you did get over 1000 views here ... I expect not a great interest in Z80 now, re problem perhaps a faulty connection on the bread board ?
     

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