////////////////////////////////////////////////////////////////////////////////
//"#use i2c(Slave,Fast,sda=PIN_C4,scl=PIN_C3,address=0x44)"                    /
//Indicates a slave address of 0x22 where a write is 0x44 and a read is 0x45:  /
//                                                                             /
//Master write: [start],[write(0x88)],[write(X)],[write(Y)],[stop]             /
//Master read:  [start],[write(0x89)],[X=read(1)],[Y=read(0)],[stop]           /
//                                                                             /
//read(1) is the same as a read(ack) and read(0) is the same as read(nack).    /
//the nack read must be the last used before a stop else the bus will be locked/
//up with sda and scl=0                                                        /
////////////////////////////////////////////////////////////////////////////////
//status     meaning                            respond with                   /
//-----------------------------------------------------------------------------/
//0x00/0x80  Address match, write block         dummy=i2c_read()               /
//0x01       First write from master=pointer    Address=i2c_read()             /
//0x02-0x7f  Subsequent writes from master=data Data=i2c_read()                /
//                                                                             /
//0x80       Address match, read block          dummy=i2c_read()               /
//0x80-0xff  Read by master from this slave     i2c_write(data[status & 0x7f]) /
////////////////////////////////////////////////////////////////////////////////
//i2c control registers for PIC16F677
#byte       sspcon              =0x14
#bit        sspen               =sspcon.5   //1=en / 0=dis
#bit        sspov               =sspcon.6
#bit        sspwcol             =sspcon.7
#byte       sspstat             =0x94
#bit        stopbit             =sspstat.4  //1=stop detected
#bit        startbit            =sspstat.3  //1=start detected
#byte       i2c_addr_reg        =0x93       //ssp address match location
////////////////////////////////////////////////////////////////////////////////
#int_SSP
static void SSP_isr(void){
unsigned    int8    i2c_register[16];       //I2C register stack
unsigned    int8    register_addr;          //for multi writes
unsigned    int8    i;
unsigned    int8    status;

//..............................................................................
restart_wdt();
if (sspwcol)
    sspwcol=0;
if (sspov)
    sspov=0;
//..............................................................................
status = i2c_isr_state();

if (status <= 0x80)                         //0x00-0x80 = data master-to-slave
    {
    i=i2c_read();
    if (status == 1)                        //address
        register_addr = i-1;
    else
        {                                   //data sent from master
        if ((status > 0) && (status < 0x80) && (register_addr < 15))
            {
            register_addr++;
            i2c_register[register_addr]=i;
            }
        }
    }

if (status >= 0x80)                         //0x80-0xff = data slave-to-master
    {
    i2c_write(i2c_register[status & 15]);
    }
//..............................................................................
}
////////////////////////////////////////////////////////////////////////////////