On the PIC18, a GOTO instruction is 4 bytes long. The second half of it,
treated as an instruction itself, is a NOP.

If you want a 2 byte branch you need to use the BRA instruction, but be
aware that unlike a GOTO, a BRA has a limited target range.

Also, a quite note: remember that program memory on the PIC18 is byte
addressed, so by sure that W is a multiple of 2 (for  BRA) or 4 (for GOTO)
before the ADDWF PCL instruction.

Bob Ammerman
RAm Systems

----- Original Message -----
From: "gtyler" <gtyler@DRUMMOND.ORG.ZA>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Saturday, January 03, 2004 1:38 AM
Subject: Appearing NOP's


> Hi, I have a strange case of appearing NOP's :)
> This is the assembly code I have written in MPLAB 6.4
> ie. what is in the .asm file:
>
> Line #
> 22       addwf PCL,1,0
> 23       goto RS0
> 24       goto RS1
> 25       goto RS2
> 26       goto RS3
> 27       return
>
> But when I assemble it, I get this in the "Program Memory" file, this is
> from the .hex file:
>
> Line#    Address
> 18          22      ADDWF 0xff9, 0x1, 0
> 19          24      GOTO 0x36
> 20          26      NOP
> 21          28      GOTO 0x42
> 22          2A      NOP
> 23          2C      GOTO 0x4c
> 24          2E      NOP
> 25          30      GOTO 0x56
> 26          32      NOP
> 27          34      RETURN 0
>
> There are strange NOP's that it has added in every 4 memory locations.
> Why does the Assembler do this? Is there any way to stop it doing this?
>
> Thanks
> Christopher Tyler
>
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