In the recent discussion regarding I2C slave during which I said I had never
needed to use the start and stop interrupts.  Typicaly, I now need to
implement a host timeout from the first start condition.  Implementing a
spare timer to achieve this is not difficult, but after a thorough read of
the datasheet I'm wondering if there is a way I can unambiguously detect
that a START interrupt has occurred from the SSPSTAT register.

The START bit in SSPSPAT will be set, but this remains set until a stop bit
is sent.  The DA bit is invalid at this stage, since no data has been
received or sent, as is the RW bit.  The only way I can think of doing this
is to have a bit variable that I initialise to zero at reset, and compare to
the START bit in SSPSTAT:

E.g.

void interrupt(void)
{
static bit prevStart = 0;       // state of START bit in previous interrupt

        if(SSPIF && SSPIE)      // is this an MSSP interrupt?
        {
                SSPIF = 0;              // clear interrupt flag
                if( (START == 1) && (prevStart == 0) ) // interrupt caused
by start?
                {
                                        // start timer etc.
                }
                else
                {
                                        // normal comms handler

                }
                prevStart = START;
        }
}


Is this a reasonable plan?  Is there a way of unambiguously detecting wether
an interrupt was caused by a a START condition just by looking at the MSSP
status register?

Cheers

Mike




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