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Does the Read-Modify-Write problem exist on the newer PICs?

Discussion in 'Embedded' started by Wouter van Ooijen, Jan 4, 2004.

  1. If I run this chip @ 40 MHz, can I do sucessive read-modify-wrte
    AFAIK it should work.
    Check the errata sheet, IIRC uChip recently documented this 'feature'.


    Wouter van Ooijen

    -- ------------------------------------
    http://www.voti.nl
    PICmicro chips, programmers, consulting
     
    Wouter van Ooijen, Jan 4, 2004
    #1
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  2. Wouter van Ooijen

    Al Borowski Guest

    Hi all,

    I'm moving towards the PIC18fxxx series fo chips for my own projects -
    currently I'm looking at the PIC18F4320.

    If I run this chip @ 40 MHz, can I do sucessive read-modify-wrte
    instructions on the port latch registers?

    EG

    bsf LATA, 0
    bcf LATA, 0

    Will this give a 100ns pulse on pin A0? I know on the earlier PICs this
    is bad practice, but what about the PIC18f4320?

    I've searched the web, and haven't found a direct answer. Piclist
    doesn't mention the 18f series on their Read-Modify-Write page.

    Also, I know some of the 18f PICs had errata that only let them run @
    4MHz. Does anyone know if this chip is affected? I can't see any mention
    of this problem in the errata sheets, but I want to make sure.

    thanks,

    Al
     
    Al Borowski, Jan 4, 2004
    #2
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  3. Wouter van Ooijen

    Jim Guest

    I think you mean this already, but just to be clear, write to the Latch
    register (e.g.LATA, LB0, LC1 etc.) rather than the port register itself
    (PORTA, RB5 etc.) If you write to the port register directly you could still
    get read-modify-write errors AFAIK.

    Jim
     
    Jim, Jan 5, 2004
    #3
  4. Wouter van Ooijen

    Al Borowski Guest

    OK, thanks. I have found many people saying it works, and no-one who
    says it doesn't.
    I have triple checked the errata sheet, no mention is made of the
    problem. Hopefully this chip isn't affected!

    thanks,

    Al
     
    Al Borowski, Jan 5, 2004
    #4
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