eMyListsDDg wrote:
>=20
> not sure i fully understand your suggestion. could you provide a a few
> lines of code for me to view?

This was after Wouter wrote:
> >
> > In most cases this will put you at the mercy of the Read-Modify-Write
> > problem. Better define a bit in a porta-shadow register, chacge that
> > bit, and copy it to PORTA after each change of any bit.

You'll find a number of examples in my tutorials
(www.gooligum.com.au/tutorials.html) - I use shadow registers pretty
consistently.

Here's one example, showing how I've set up a shadow register as a union,
making it possible to refer to the whole register ("GPIO =3D sGPIO.port") o=
r
to individual shadow bits with logical names ("sFLASH =3D 1").  Don't be
scared off - the lessons start simpler than this!


/************************************************************************
*                                                                       *
*   Description:    Lesson 3, example 4                                 *
*                                                                       *
*   Demonstrates use of Timer0 in counter mode                          *
*                                                                       *
*   LED flashes at 1 Hz (50% duty cycle),                               *
*   with timing derived from 32.768 kHz input on T0CKI                  *
*                                                                       *
*************************************************************************
*                                                                       *
*   Pin assignments:                                                    *
*       GP1   =3D flashing LED                                            *
*       T0CKI =3D 32.768 kHz signal                                       *
*                                                                       *
************************************************************************/

#include <htc.h>
#include <stdint.h>


/***** CONFIGURATION *****/
// ext reset, no code protect, no watchdog, int RC clock
__CONFIG(MCLRE_ON & CP_OFF & WDT_OFF & OSC_IntRC);

// Pin assignments
#define sFLASH  sGPIO.GP1           // flashing LED (shadow)


/***** GLOBAL VARIABLES *****/
union {                             // shadow copy of GPIO
    uint8_t         port;
    struct {
        unsigned    GP0     : 1;
        unsigned    GP1     : 1;
        unsigned    GP2     : 1;
        unsigned    GP3     : 1;
        unsigned    GP4     : 1;
        unsigned    GP5     : 1;
    };
} sGPIO;


/***** MAIN PROGRAM *****/
void main()
{
    // Initialisation
   =20
    // configure port   =20
    TRIS =3D 0b111101;                // configure GP1 (only) as an output
   =20
    // configure timer   =20
    OPTION =3D 0b11110110;            // configure Timer0:
             //--1-----                 counter mode (T0CS =3D 1)
             //----0---                 prescaler assigned to Timer0 (PSA =
=3D
0)
             //-----110                 prescale =3D 128 (PS =3D 110)
             //                         -> increment at 256 Hz with 32.768
kHz input
                =20
    // Main loop
    for (;;)
    {
        // TMR0<7> cycles at 1 Hz, so continually copy to LED
        sFLASH =3D 0;                 // assume TMR<7>=3D0 -> LED off
        if (TMR0 & 1<<7)            // if TMR0<7>=3D1
            sFLASH =3D 1;             //   turn on LED
       =20
        GPIO =3D sGPIO.port;          // copy shadow to GPIO
       =20
    }   // repeat forever
}


--=20
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