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  1. #1
    Join Date
    Apr 2014
    Posts
    58

    Default Speed of commands

    I used a PIC12F1501 to try a little experiment. I wanted to see how much faster LATx.y = z works than HIGH PORTx.y. So here's the premise; 4 MHz OSC, LOOOOONNNGG DO/LOOP, and an LED that tells me which version I'm looking at. Here is the short version:

    DO
    HIGH LED
    FOR w0 = 1 to 10000
    HIGH PORTA.2
    LOW PORTA.2
    HIGH PORTA.2
    LOW PORTA.2
    (about 32 times)
    NEXT w0
    LOW LED
    FOR w0 = 1 to 10000.
    LATA.2 = 1
    LAT.2 = 0
    (another 32 times)
    NEXT w0
    LOOP

    I found commanding the LAT register to be about 3 times faster than using the HIGH/LOW commands. Just wanted to share.

  2. #2
    Join Date
    Jan 2006
    Location
    Istanbul, The Only City and The Only Place That Connects Two Continents
    Posts
    1,109

    Default Re: Speed of commands

    HIGH and LOW commands first set the corresponding pin(s) to be output; then change the state of the pin to 1 or 0.

    Therefore, it produces a few more lines of code behind; and it takes longer time.
    "If the Earth were a single state, Istanbul would be its capital." Napoleon Bonaparte

  3. #3
    Join Date
    Aug 2003
    Location
    Australia
    Posts
    924

    Default Re: Speed of commands

    Yes you should be doing porta.2 = 1 once tris is setup once at the beginning.
    That would hopefully translate to a single set bit instruction.

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