What I mean is this:  Within FL51XINC.ASM are lines such as -

        movlw   (0x01 << SDA)   ; make SDA an input
        tris    I2C_PORT
and
        movlw   0x00            ; make sure both are outputs
        tris    I2C_PORT

(this is really indended to configure 2 bits of the single GP I/O port
but if I wanted some other bits to be inputs, this code snippit would
change them to outputs, right?  Also, I see in section 4.4 of the 12C5XX
data sheet that setting a TRIS bit to '0' would disable the wake-up on
change, and weak pullup function for the corresponding pin).

So, wouldnt the "correct" way be to assign a shadow register -
        cblock
        TRIS_SHADOW
        ... (other data registers)
        endc

{along with some bit definitions -
        GP0     EQU     0       ;I wanna use this as an input
        GP1     EQU     1       ;I wanna use this as an input
        GP2     EQU     2       ;I wanna use this as an output
        SDA     EQU     3       ;Bi directional
}

and in my main code -
        movlw   (0x01 << GP0) | (0x01 << GP1)           ; GP0 & GP1 an input
        movwf   TRIS_SHADOW
        tris    I2C_PORT

and when I want to make SDA and input -
        movf    TRIS_SHADOW, w
        iorlw   (0x01 << SDA)   ;generate OR mask
        movwf   TRIS_SHADOW
        tris    I2C_PORT

and when I want to make SDA and output -
        movf    TRIS_SHADOW, w
        andlw   ~(0x01 << SDA)  ;generate AND mask
        movwf   TRIS_SHADOW
        tris    I2C_PORT


Or is this really overkill?
Thanks

Mike Garber





> -----Original Message-----
> From: Dwayne Reid [mailto:dwayner@PLANET.EON.NET]
> Sent: Saturday, July 07, 2001 1:52 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [PIC]: 12CE5xx & FL51XINC.ASM & Internal EEPROM
>
>
> At 04:38 PM 7/6/01 -0400, Garber, Mike wrote:
>
> >Also, I notice that within FL51XINC.ASM, the TRIS instruction is used
> >repeatedly.
> >Shouldnt a better way be to use a "shaddow" register to hold
> the value
> >sent, so that
> >the configuration of GP0 thru GP5 doesnt get screwed up from
> the direction
> >I want
> >them to be from my main program?
>
> The 12c5xx parts use the 12 bit core.  Thus, the ONLY way you
> can change
> the TRIS bits is to use the TRIS instruction.
>
> dwayne
>
>
>
> Dwayne Reid   <dwayner@planet.eon.net>
> Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
> (780) 489-3199 voice          (780) 487-6397 fax
>
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