PHXSYS wrote:
>
> Hi everyone
>
> In my program I am using the program counter to sequence several routines. I
> am using it like this:
>
> MOVF   SSTATE,W
> MOVWF PCL
>
> SSTATE is the address of the specific routine. My problem is SSTATE is an 8
> bit value and my routine length goes over 255 addresses. When it goes over 255
> it goes to the beginning of the program. I use the PAGE command before and
> after routines, but it must be larger than a page.

Yes, as I wrote in an answer to previous question you posted, if you
want to use this technique and your code extends over 256 memory
locations you have to play with PCLATH.

> I have to keep the code efficient because of the serial timing, I don't have
> much room for additional code.
>
> What are my options?
>
> Is there an efficient way to make SSTATE a 16bit number and will that even
> work? For example if SSTATE was at 355 would the program counter no where to
> go?

You can use two register for the SState value (i.e. SStateL and SStateH)
to hold a 16 bit number.

So, using the code fragment you posted in "MOVLW where the literal is a
label", the sequence:

>         movlw   Ckstrt          ; then make sure start bit persists**** LOOK H
ERE
>         movwf   SState
>         goto    w10
> ;
> Ckstrt  decfsz  STime,F  ; verify start bit by sampling at center **** LOOK HE
RE

becomes:

        movlw   high Ckstrt     ; Get the high addr of the 'Ckstrt'
routine
        movwf   SStateH         ; Store in high register
        movlw   low Ckstrt      ; Get the low address byte
        movwf   SStateL         ; Store in low register
        goto    w10
;
Ckstrt  decfsz  STime,F  ; verify start bit by sampling at center ****
LOOK HERE

Then, when your state machine has to call the appropriate routine use:

        movf        SStateH, W    ;Load the high byte of address
        movwf       PCLATH        ;Set the PCLATH register
        movf        SStateL, W    ;Load the low byte of the routine
address
        movwf       PCL           ;Jump to the routine at
SStateH:SStateL

> Can I use a lookup table to provide any additional options? For example
> offset the counter to GOTO's. I don't think I can do that.
>
> Is there a way to utilize a lookdown table?

Yes, you can also build a jump table and use an index rather than the
routine address for SState in a form like this:

        movlw   0          ; 0 stands for 'Ckstrt' (you can also use
#define's
        movwf   SState     ; to make your code more readable)
        goto    w10

Then to dispatch to the proper routine:

        movlw   high table ; Make sure PCLATH points to the current code
page
        movwf   PCLATH
        movf    SState,W   ; Get the index in the table
        addwf   PCL, F     ; Jump to the proper entry
table   goto    SState     ; Index 0
        goto    Getbit     ; Index 1
        goto    ...        ; Index ...

Ciao
  Marco

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