Need help on I2C slave please

[armstrong800]

Hello folks, I have just picked up the CCS C compiler software for my project. I am using one PIC 16F877 as a slave in a single master I2C configuration. A Motorola�s HCS12 acts as a master. First thing that made me uncomfortable was that the C language I learned before isn�t usable in CCS as it seems to have its own syntax. I like the idea of pre processor, but for a new comer like me I feel it is hard to understand how to use them even after read the CCS manual. And the example codes are a little too complicated for me now. I managed to tailor up this program from what I have learnt from several codes I found to initiate the slave function of the PIC but it is not working. My partner and I have been spending some time on this little thing. Would anyone please shed some light on how to correct this program? A lot thanks ahead.

My partner's master has been tested to work, so it must be my program that is wrong. Here it is. All I want is just being able to receive and transmit bytes.

#if defined(__PCM__) // preprocessor directive that chooses the compiler
#include <16F877.h>
#fuses XT,NOWDT,NOLVP
#use delay(clock=4000000)
//#use I2C(slave,sda=PIN_C4,scl=PIN_C3,address=0xa0,FAST = 450000, FORCE_HW)

#byte SSPSTAT = 0x94
#byte SSPCON = 0x41
#byte SSPADD = 0x41
#byte PIE1 = 0x41
#byte PIR1 = 0x0c
#byte TRISC = 0x87
#byte SSPBUF = 0x13
#byte Inputt = 0x6800
#define Stop_bit PIN_d4
#define buffer_full PIN_d0

#INT_SSP
void i2c_slave_interrupt ()
{
byte input;
byte tempI2C;
input = SSPSTAT;
if (Input(Stop_bit)==1) // If the stop bit of the SPSTAT is a one then the slave is to transmit (why is that ?? Is a stop bit the last bit it receives??) {
//I2C Slave Transmission
SSPBUF = 0; // clear the SSPBUF
bit_set(SSPCON,4); // CKP, SSPBUFF must be write before
bit_clear(PIR1,3); //reset the interrupt flag
}
else
{
//I2C Slave Reception
tempI2C = SSPBUF;
bit_clear(PIR1,3); //reset the interrupt flag

}
}


void init_i2c_slave()
{
bit_set(SSPSTAT,7); // standard speed mode
bit_clear(SSPSTAT,6); // input level conform to I2C spec
bit_clear(SSPSTAT,0); // BF buffer full bit

//SCL and SDA as input
bit_set(TRISC,3);
bit_set(TRISC,4);

//SSPCON<5> enable bit (1)
//SSPCON<3> 0110 (slave, 7 bits address)
bit_clear(SSPCON,7); // WCOL Write Collision Detect bit
bit_clear(SSPCON,6); // SSPOV Receive Overflow Indicator bit
bit_set(SSPCON,5); // Synchronous Serial Port Enable
bit_set(SSPCON,4); // CKP
bit_clear(SSPCON,3); //0110: I2C slave mode: 7 bits address
bit_set(SSPCON,2);
bit_set(SSPCON,1);
bit_clear(SSPCON,0);

SSPADD=0x0E; // 0000 1110 -> 7 bits address= 0000 111
//SSP
bit_set(PIE1,3);
bit_clear(PIR1,3);
}
void main ()
{
init_i2c_slave();
SET_TRIS_B(0x00);

inputt = SSPBUF &0x01; // (just to see if the SSPBUF is ever filled)
while(1)
{
if (Inputt==1){
output_high (PIN_B7);
delay_ms(1000);
output_low (PIN_B7);
delay_ms(1000);
}

}
}

[PCM programmer]

I suggest that you start with the CCS example, Ex_Slave.c.
Here's the file location:
c:\program files\picc\examples\ex_slave.c

Here's some simple master code in this post, which sends a single
character to a PIC running Ex_Slave.c, and then reads it back.
http://www.ccsinfo.com/forum/viewtopic.php?t=28097&start=9

Remember that you need pullup resistors (4.7K will work) on SDA
and SCL, and you need a ground connection between the two boards.