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#include "874modbu.h"

#define SlaveAddress 1

int isrEnd,readEnd;

bank1 unsigned char buffer[74];

union transform{

struct twoBytes{

unsigned char lowByte;

unsigned char highByte;

}bytes;

unsigned int integer;

}T;

void delay(unsigned int time)

{

unsigned int i,j;

for (i = 0; i

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BRGH = 0;

SPBRG = 31; // baud rate 9600 for 20 MHz

SYNC = 0;

SPEN = 1; // serial port pins ON

CREN = 1;

SREN = 0;

TXIE = 0;

RCIE = 0;

TX9 = 0;

RX9 = 0;

TXEN = 1;

}

void startI2C(void)

{

SEN = 1;

while (SEN);

}

void stopI2C(void)

{

PEN = 1;

while (PEN);

}

unsigned char readRS(vid)

{

while(!RCIF) continue;

return RCREG;

}

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void writeRS(unsigned char c)

{

TXREG = c;

TXEN = 1;

while (!TRMT);

}

unsigned char readI2C(void)

{

isrEnd = 0;

while(!isrEnd);

PEN = 1;

while (PEN);

return SSPBUF;

}

void writeI2C(unsigned char data)

{

isrEnd = 0;

SSPBUF = data;

while (!isrEnd);

while (ACKSTAT);

}

bit CRC16(unsigned int dataLength,char check) //CRC 16 for modbus checksum

{

unsigned int CheckSum;

unsigned int j;

unsigned char lowCRC;

unsigned char highCRC;

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unsigned short i;

CheckSum = 0xffff;

for (j=0; j0;i--)

if((CheckSum)&0x0001)

CheckSum = (CheckSum>>1)^0xa001;

else

CheckSum>>=1;

}

highCRC = CheckSum>>8;

CheckSum8;

if (check==1){

if ( (buffer[dataLength+1] == highCRC) & (buffer[dataLength] == lowCRC ))

return 1;

else

return 0;

}

else

{

buffer[dataLength] = lowCRC;

buffer[dataLength+1] = highCRC;

return 1;

}

}

void readRegResponse(void) //response for modbus 03 function (read registers)

{

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unsigned char i;

T.bytes.lowByte = buffer[3];

T.bytes.highByte = buffer[2];

T.integer*=2;

buffer[2] = buffer[5]*2;

for (i=0; i

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CRC16(3,0);

for (i=0; i

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while((!RCIF) && (j < 30000)) j++;

return RCIF;

}

unsigned char ReadMBFrame()

{

unsigned int counter = 0;

unsigned int aux;

stop = 0;

while (!stop)

if(!CheckRSInBuffer())

stop = 1;

else

{

if (counter 74) return 2; //to many bytes in frame

if (counter < 8) return 0; //to few bytes frame

if (buffer[0] != SlaveAddress) return 0; //wrong address

if ((buffer[1] != 3) & (buffer[1] != 16))return 1; //wrong modbus function

aux = (unsigned int)buffer[2] * 255 + (unsigned int)buffer[3] + (unsigned int)buffer[4]*255+(unsigned int)buffer[5];

if (aux > 8000) return 2; // to many registers

if ((buffer[4]>0)|( buffer[5] > 32)) return 2; // to many registers

if( CRC16(counter - 2,1))

return buffer[1]; //OK

else

return 0; //bad CRC

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}

void setISR(void) /*Sets ISR bits */

{

GIE = 1;

PEIE = 1;

RCIE = 0;

SSPIE = 1;

EEIE = 1;

}

void I2CInitialize(void)

{

SSPEN = 1;

SSPM3 = 1;

SSPM2 = 0;

SSPM1 = 0;

SSPM0 = 0;

SSPADD = 12;

}

void interrupt isr(void)

{

if (SSPIF)

{

SSPIF = 0;

isrEnd = 1;

}

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}

void main(void)

{

unsigned char c;

c = 1;

TRISB = 0xE0;

TRISC = 0xF8;

RB1 = 0;

RB2 = 0;

RC3 = 1;

RC4 = 1;

setISR();

I2CInitialize();

setRS();

for(;;)

{

if (RCIF) {

c =ReadMBFrame();

if (c == 3)

readRegResponse();

else

if (c==16)

writeRegResponse();

else

writeBadRequest(c);

}

}

}