8255 of MC6821?

Discussion in 'Embedded Systems and Microcontrollers' started by Tera-Scale, Sep 12, 2011.

  1. Tera-Scale

    Thread Starter Active Member

    Jan 1, 2011
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    Hi,
    I need to know which factors I need to look for in interfacing a 16-bit flash adc to a microcontroller (high speed parallel interface) with either 8255 PPI or MC6821 PIA. I need to determine which is the best option and why.

    thanks
     
    Last edited: Sep 12, 2011
  2. t06afre

    AAC Fanatic!

    May 11, 2009
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    What kind of flash ADC do you use? Why do you need a PPI/PIA circuit. If you have enough free MCU ports to interface a PPI/PIA. You should also be able to interface the ADC directly to the MCU
     
  3. Tera-Scale

    Thread Starter Active Member

    Jan 1, 2011
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    thanks for the reply. You are right but strangely enough this question this question was in a Past Paper and I would liked to have some clues if i were to do it. thanks
     
  4. stahta01

    Member

    Jun 9, 2011
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    The answer likely depends on details of the ADC and MCU.

    This assumes the MCU has a 8-bit data bus; if it is not a 8-bit data bus than both of them are likely bad choices.

    Does the MCU/ADC have/need an external interrupt?
    How many I/O pins are really needed?
    IIRC 8255 has more I/O pins
    And, IIRC 6821 does interrupts better.

    Tim S.
     
    Last edited: Sep 12, 2011
  5. Tera-Scale

    Thread Starter Active Member

    Jan 1, 2011
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    The MCU is not specified. " Evaluate and justify with technical reasons which of the two peripheral inteface devices you would choose for a high speed parallel interface from a microcontroller board to a 16-bit Flash ADC."

    Is it refering to the speeds .. any ideas?

    thanks
     
  6. stahta01

    Member

    Jun 9, 2011
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    The 8255 was used longer in new production; so, it might have gotten faster than the 2 or 3 MHz that I think the MC6821 stopped at.

    Tim S.
     
  7. MrChips

    Moderator

    Oct 2, 2009
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    You may want to consider that this is a trick question.
    Why do you want to use a 16-bit Flash ADC?
    Most Flash ADCs are used instead of successive approximation ADCs when the sampling rate exceeds 2Msps or there about.
    Typically, Flash ADCs are used at sampling rates greater than 20Msps, in which case neither 8255 nor 6821 would be useful.
    To take full advantage of the speed of a 16-bit Flash ADC you would require a 16-bit data bus.
    In which case I would be using a DSP and not an MCU.
     
  8. Tera-Scale

    Thread Starter Active Member

    Jan 1, 2011
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    Thanks a lot for your help. It makes a lot of sense. I wonder if these chips are still manufactured.
     
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