TONY NIXON 54964 <PICLIST@MITVMA.MIT.EDU> wrote:

> It's interesting that if you move a value directly into PCL then the
> next instruction is fetched from that address value. If you ADD a
> value into PCL the next instruction is fetched from the result + 1.

    Not exactly, Tony.

    The PIC increments PCL BEFORE executing the current instruction.
    Here's an example:

        0000        CLRF    PCLATH
        0001        MOVLW   2
        0002        ADDWF   PCL

    The Program Counter starts at address 0000.

    The PIC grabs the "CLRF PCLATH" instruction, then increments the
    PC (so PCL = 1), then executes the CLRF.

    Next, the PIC grabs the instruction at address 0001 (since the
    Program Counter holds 0001), then increments the Program Counter
    (so PCL = 2), then executes the MOVLW.

    Next the PIC grabs the instruction at address 0002 (since the
    Program Counter now holds 0002), then increments the Program
    Counter (so PCL = 3), THEN performs the ADDWF.  Since PCL = 3
    when the addition occurs, the result of the ADDWF PCL is 5
    (since 3 + 2 = 5).

    The Program Counter, therefore, holds 0005 after the ADDWF.

    -Andy

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=== 6:30 pm on Wednesday, 1 October, at Bytecraft Limited's booth.
===
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