EX_CRC.C
---------------------------------------------------------------------------
/////////////////////////////////////////////////////////////////////////
//// EX_CRC.C ////
//// ////
//// This example program shows how to send messages between two ////
//// PICs using CRC error checking. Pushing button 40 on the ////
//// prototype card sends a message from that PIC to any other PICs ////
//// that are connected. The receiving PIC then sends back an ACK ////
//// after it correctly receives the message. ////
//// ////
//// Two seperate PICs are needed for this example. Compile the ////
//// code as is and program the first PIC. Then switch the ////
//// MACHINE_ADDRESS and SEND_ADDRESS and program the second PIC. ////
//// ////
//// ////
//// Packet Protocol: ////
//// +------------+--------------+---------+--------+------+-----+ ////
//// | Address TO | Address FROM | Control | Length | Data | CRC | ////
//// +------------+--------------+---------+--------+------+-----+ ////
//// ////
//// Address TO: 1 byte Address of sending PIC ////
//// Address FROM: 1 byte Address of receiving PIC ////
//// Control: 1 byte Used for ACK and NACK ////
//// Length: 2 bytes Number of bytes in Data field ////
//// Data: 0 to N bytes Data being sent ////
//// CRC: 2 bytes 16 Bit CRC ////
//// ////
//// Configure the CCS prototype card as follows: ////
//// Jumper from PIC 1 pin 47 (B0) to PIC 2 pin 48 (B1) ////
//// Jumper from PIC 1 pin 48 (B1) to PIC 2 pin 47 (B0) ////
//// Jumper from PIC 1 pin 27 (GND) to PIC 2 pin 27 (GND) ////
//// Jumper from PIC 1 pin 40 (Switch) to PIC 1 pin 49 (B2) ////
//// Jumper from PIC 2 pin 40 (Switch) to PIC 2 pin 49 (B2) ////
//// See additional connections below. ////
//// ////
//// This example will work with the PCM and PCH compilers. The ////
//// following conditional compilation lines are used to include a ////
//// valid device for each compiler. Change the device, clock and ////
//// RS232 pins for your hardware if needed. ////
//// ////
/////////////////////////////////////////////////////////////////////////
//// (C) Copyright 1996,2001 Custom Computer Services ////
//// This source code may only be used by licensed users of the CCS ////
//// C compiler. This source code may only be distributed to other ////
//// licensed users of the CCS C compiler. No other use, ////
//// reproduction or distribution is permitted without written ////
//// permission. Derivative programs created using this software ////
//// in object code form are not restricted in any way. ////
/////////////////////////////////////////////////////////////////////////
#if defined(__PCM__)
#include <16F877.H>
#device *=16
#fuses HS,NOWDT,NOPROTECT
#use delay(clock=20000000)
#use rs232(baud=9600, xmit=PIN_B1, rcv=PIN_B0)
#elif defined(__PCH__)
#include <18C452.H>
#fuses HS,NOPROTECT
#use delay(clock=20000000)
#use rs232(baud=9600, xmit=PIN_B1, rcv=PIN_B0)
#endif
#include
// CONSTANTS
#define MACHINE_ADDRESS 0x01
#define SEND_ADDRESS 0x02
#define ACK 0x01
#define NACK 0xFF
#define BUFFER_SIZE 64
// GLOBAL VARIABLES
int packet_buffer[BUFFER_SIZE];
int ext_buffer[BUFFER_SIZE];
int ext_buffer_next_in;
int ext_buffer_next_out;
#define MESSAGE_SEND (!input(PIN_B2))
#define DATA_IN (ext_buffer_next_in != ext_buffer_next_out)
// EXTERNAL INTERRUPT
// function for reading in bytes from other PIC
#INT_EXT
ext_isr()
{
ext_buffer[ext_buffer_next_in] = getc(); // get a byte, put it in buffer
if(++ext_buffer_next_in == BUFFER_SIZE) // increment counter
ext_buffer_next_in = 0;
}
// GET_BUFF_INT
// function to extract bytes from the buffer
int get_buff_int()
{
int retval;
while(!DATA_IN); // wait until data available
retval = ext_buffer[ext_buffer_next_out]; // get the byte
if(++ext_buffer_next_out == BUFFER_SIZE) // increment counter
ext_buffer_next_out = 0;
return retval;
}
// SEND_PACKET
// function to send a packet of data to another PIC
void send_packet(int* packet_ptr, int16 packet_length)
{
int *ptr;
int16 CRC,i;
ptr = packet_ptr; // set pointer
CRC = generate_16bit_crc(ptr, packet_length, CRC_CCITT);
// make CRC
for(i=0; i>8)); // send CRC
putc((int)(CRC));
}
// GET_PACKET
// function to get a packet from the buffer and read the data
short get_packet(int* packet_ptr)
{
short retval;
int16 length;
int16 CRC;
int16 i;
retval = TRUE;
packet_ptr[0] = get_buff_int(); // get the address of send to
packet_ptr[1] = get_buff_int(); // get the address of send from
if(packet_ptr[0] != MACHINE_ADDRESS)
retval = FALSE;
packet_ptr[2] = get_buff_int(); // get the control byte
if(packet_ptr[2] == NACK)
retval = FALSE;
packet_ptr[3] = get_buff_int(); // get the length of the data
packet_ptr[4] = get_buff_int();
length = (int16)(packet_ptr[3])<<8;
length += packet_ptr[4];
for(i=5; i<(length+5); i++) // get the data
packet_ptr[i] = get_buff_int();
packet_ptr[length+5] = get_buff_int(); // get the CRC
packet_ptr[length+6] = get_buff_int();
CRC = (int16)(packet_ptr[length+5])<<8;
CRC += packet_ptr[length+6];
if(CRC != generate_16bit_crc(packet_ptr, length+5, CRC_CCITT))
retval = FALSE;
return retval;
}
// Change RS-232 IO pins
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7) // Jumpers: 8 to 11, 6 to 14
main() {
ext_buffer_next_in = 0; // init variables
ext_buffer_next_out = 0;
ext_int_edge(H_TO_L); // init interrupts
enable_interrupts(INT_EXT);
enable_interrupts(GLOBAL);
while(TRUE) // loop always
{
int i;
if(MESSAGE_SEND) // if button pushed
{
packet_buffer[0] = SEND_ADDRESS;
packet_buffer[1] = MACHINE_ADDRESS;
packet_buffer[2] = 0;
packet_buffer[3] = 0;
packet_buffer[4] = 9;
packet_buffer[5] = 'H';
packet_buffer[6] = 'i';
packet_buffer[7] = ' ';
packet_buffer[8] = 't';
packet_buffer[9] = 'h';
packet_buffer[10] = 'e';
packet_buffer[11] = 'r';
packet_buffer[12] = 'e';
packet_buffer[13] = '!';
send_packet(packet_buffer, 14); // send message
}
delay_ms(100);
if(!DATA_IN) // if no data in
continue; // loop back
if(get_packet(packet_buffer)) // if valid packet
{
int16 length,i;
int16 CRC;
printf("Message from unit# %U\n",packet_buffer[1]);
length = ((int16)(packet_buffer[3]<<8)) + packet_buffer[4];
if(packet_buffer[2] == ACK)
printf("Previous message sent was received by unit.\n");
if(length) // display message
{
printf("Message is:\n\n");
for(i=0;i