1. 存儲區代號

2. 功能碼

3. pymodbus服務器

from pymodbus.server.async_io import StartTcpServer
from pymodbus.datastore import (
    ModbusSequentialDataBlock,
    ModbusServerContext,
    ModbusSlaveContext,
)

datablock = ModbusSequentialDataBlock.create()
context = ModbusSlaveContext(
    di=datablock,
    co=datablock,
    hr=datablock,
    ir=datablock,
    )
single = True

# Build data storage
store = ModbusServerContext(slaves=context, single=single)


if __name__ == '__main__':

	address = ("127.0.0.1", 1502)
	StartTcpServer(
	    context=store,  # Data storage
	    address=address,  # listen address
	  	allow_reuse_address=True,  # allow the reuse of an address
	)

4. libmodbus客戶端

#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <errno.h>
#include <modbus/modbus.h>
#include <time.h>


// const uint16_t UT_INPUT_REGISTERS_ADDRESS = 0x1;
const uint16_t UT_BITS_ADDRESS = 0x04;
// const uint16_t UT_INPUT_REGISTERS_NB = 0xA;
// const uint16_t UT_INPUT_REGISTERS_TAB[] = { 0x000A };

int main(int argc, char const *argv[])
{
    int nb = 0x08;
    int rc = 0;
    modbus_t *ctx;
    uint8_t *tab_rp_bits;
    tab_rp_bits = (uint8_t *) malloc(nb * sizeof(uint8_t));
    memset(tab_rp_bits, 0, nb * sizeof(uint8_t));
    ctx = modbus_new_tcp("127.0.0.1", 1502);
    if(ctx == NULL)
    {
        fprintf(stderr, "Unable to allocate libmodbus context\n");
        return -1;
    }

    if(modbus_connect(ctx) == -1)
    {
        fprintf(stderr, "Connection failed: %s\n", modbus_strerror(errno));
        modbus_free(ctx);
        return -1;
    }
    uint8_t data[8] = {1, 0, 1, 0, 1, 1, 0, 1};
    while(1)
    {
        // rc = modbus_write_bit(ctx, UT_BITS_ADDRESS, 1);
        rc = modbus_write_bits(ctx, UT_BITS_ADDRESS, nb, data);
        printf("nb points %d : ", rc);

        rc = modbus_read_bits(ctx, UT_BITS_ADDRESS, 8, tab_rp_bits);
        if (rc != 1) 
        {
            for (size_t i{0}; i < 8; i++)
                // printf("FAILED (nb points %d)\n", rc);
                printf("%d  ", tab_rp_bits[i]);
        }
        printf("\n");
        memset(tab_rp_bits, 0, nb * sizeof(uint8_t));
        sleep(1);
    }
    modbus_close(ctx);
    modbus_free(ctx);
    return 0;
}