> Hi folks,
>     I'm with problems when doing a "computed goto" with a PIC18F4680.
>
>     I've debugged a lot of times and I don't know what's happening.
>
>     I did a sample program to illustrate my problem:
>
> The code below works fine because the "computed goto" program area don't
> change the PCLATH value. PCLATH always is zero.
>
> -----------------------------------------------------------------------
> PROGRAM   CODE 0x0030
> Program:
> goto Main
>
>
> ANOTHER_AREA CODE 0x80
> Main:
>  movlw .2
>  addwf PCL
>  goto Main0
>  goto Main2
>  goto Main4
>
> Main0:
>  nop
>  goto Main
>
> Main2:
>  nop
>  goto Main
>
> Main4:
>  nop
>  goto Main4
> --------------------------------------------------------------------------
>
> However, IF the Main routine is in 0x100 program memory area (or 0x200,
> 0x300, and so on), the problem happens and after the addwf a jump to a
> 0x0nn
> area is performed.
>
> THIS CODE DOESN'T
> WORKS--------------------------------------------------------------------------------------------------------------
> PROGRAM   CODE 0x0030
> blProgram:
>  goto Main
>
>
> ANOTHER_AREA CODE 0x100
> Main:
>  movlw .2
>  addwf PCL
>  goto Main0
>  goto Main2
>  goto Main4
>
> Main0:
>  nop
>  goto Main
>
> Main2:
>  nop
>  goto Main
>
> Main4:
>  nop
>  goto Main4
> --------------------------------------------------------------------------------------------------------------------------------------------------
>
>
> I see in simulator that PCLATH value never is changed. So, when I use
> ADDWF
> PCL, the program jumps to a 0nn relative area insted 1nn.
>
> "goto" shouldn't change the complete program counter?
>
> Anybody know what I'm doing wrong??
>
> Sorry my bad english but I hope you understood me.
>
> Thanks,
> Eduardo Garcia
>


Your English is fine!

The goto changes the full program counter, but the addwf PCL ONLY changes
PCL.

I'd do something like this:


     movlw high(JumpTable)  ; set pclath to start of jump table
     movwf PCLATH
     RLFNC state,w          ; get state*2 since each bra takes 2 addresses
     addwf low(JumpTable),w ; add in low half of start of table
     skpnc
     incf  PLCATH,f         ; add carry if needed
     movwf PCL              ; jump into table
JumpTable
     bra main0
     bra main1
     bra main2

Note the use of bra instead of goto. If you use goto, you'll have to
allocate 4 addresses per state. Using bra lets you do a RLFNC to multiply
by two as you get the state into w.

Hope that helps!

Harold
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