用c语言写一段MODBUS协议
时间: 2023-10-15 19:03:20 浏览: 38
好的,这是一份使用C语言编写的Modbus协议:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAX_PDU_LEN 260
/*
* Modbus Function Codes
*/
#define FUNC_READ_COILS 0x01
#define FUNC_READ_INPUTS 0x02
#define FUNC_READ_HOLD_REGS 0x03
#define FUNC_READ_IN_REGS 0x04
#define FUNC_WRITE_COIL 0x05
#define FUNC_WRITE_HOLD_REG 0x06
/*
* Modbus Exception Codes
*/
#define EXCEPT_ILLEGAL_FUNC 1
#define EXCEPT_ILLEGAL_ADDR 2
#define EXCEPT_ILLEGAL_VAL 3
#define EXCEPT_SLAVE_FAIL 4
#define EXCEPT_ACK 5
#define EXCEPT_SLAVE_BUSY 6
int main(int argc, char **argv) {
unsigned char pdu[MAX_PDU_LEN];
int pdu_len = 0;
// Set up the Modbus request packet
// Function Code: Read Holding Registers (0x03)
pdu[pdu_len++] = FUNC_READ_HOLD_REGS;
// Starting Address (Register #): 0x0000
pdu[pdu_len++] = 0x00; // HiByte
pdu[pdu_len++] = 0x00; // LoByte
// Number of Registers to Read: 0x0002
pdu[pdu_len++] = 0x00; // HiByte
pdu[pdu_len++] = 0x02; // LoByte
// Send the packet to the Modbus Slave
// Assume this is done by a function called modbus_send
modbus_send(pdu, pdu_len);
// Wait for response from the Modbus Slave
// Assume this is done by a function called modbus_recv
modbus_recv(pdu, &pdu_len);
// Process the response from the Modbus Slave
// Check Function Code
if(pdu[0] == FUNC_READ_HOLD_REGS) {
// Check Byte Count (Number of Bytes Following)
int byte_count = pdu[1];
if(byte_count == 4) {
// Extract the Register Values (Big Endian)
int value1 = (pdu[2] << 8) | pdu[3];
int value2 = (pdu[4] << 8) | pdu[5];
printf("Register Values: %d, %d\n", value1, value2);
} else {
printf("Modbus Exception: Invalid Byte Count\n");
}
} else if(pdu[0] == (0x80 | FUNC_READ_HOLD_REGS)) {
// Modbus Exception
int except_code = pdu[1];
printf("Modbus Exception: ");
switch(except_code) {
case EXCEPT_ILLEGAL_FUNC:
printf("Illegal Function\n");
break;
case EXCEPT_ILLEGAL_ADDR:
printf("Illegal Data Address\n");
break;
case EXCEPT_ILLEGAL_VAL:
printf("Illegal Data Value\n");
break;
case EXCEPT_SLAVE_FAIL:
printf("Server Device Failure\n");
break;
case EXCEPT_ACK:
printf("Acknowledge\n");
break;
case EXCEPT_SLAVE_BUSY:
printf("Server Device Busy\n");
break;
default:
printf("Unknown (%d)\n", except_code);
break;
}
} else {
printf("Invalid Modbus Response\n");
}
return 0;
}