Trait libmodbus::ModbusClient

pub trait ModbusClient {
    fn read_bits(
        &self, 
        address: u16, 
        num: u16, 
        dest: &mut [u8]
    ) -> Result<u16, Error>;
    fn read_input_bits(
        &self, 
        address: u16, 
        num: u16, 
        dest: &mut [u8]
    ) -> Result<u16, Error>;
    fn read_registers(
        &self, 
        address: u16, 
        num: u16, 
        dest: &mut [u16]
    ) -> Result<u16, Error>;
    fn read_input_registers(
        &self, 
        address: u16, 
        num: u16, 
        dest: &mut [u16]
    ) -> Result<u16, Error>;
    fn report_slave_id(
        &self, 
        max_dest: usize, 
        dest: &mut [u8]
    ) -> Result<u16, Error>;
    fn write_bit(&self, address: u16, status: bool) -> Result<(), Error>;
    fn write_bits(
        &self, 
        address: u16, 
        num: u16, 
        src: &[u8]
    ) -> Result<u16, Error>;
    fn write_register(&self, address: u16, value: u16) -> Result<(), Error>;
    fn write_registers(
        &self, 
        address: u16, 
        num: u16, 
        src: &[u16]
    ) -> Result<u16, Error>;
    fn write_and_read_registers(
        &self, 
        write_address: u16, 
        write_num: u16, 
        src: &[u16], 
        read_address: u16, 
        read_num: u16, 
        dest: &mut [u16]
    ) -> Result<u16, Error>;
    fn mask_write_register(
        &self, 
        address: u16, 
        and_mask: u16, 
        or_mask: u16
    ) -> Result<(), Error>;
    fn send_raw_request(
        &self, 
        raw_request: &mut [u8], 
        lenght: usize
    ) -> Result<u16, Error>;
    fn receive_confirmation(&self, response: &mut [u8]) -> Result<u16, Error>;
}

The Modbus protocol defines different data types and functions to read and write them from/to remote devices. The following functions are used by the clients to send Modbus requests:

• Read data
  • read_bits(), read_input_bits(), read_registers(), read_input_registers(), report_slave_id()
• Write data
  • write_bit(), write_register(), write_bits(), write_registers()
• Write and read data
  • write_and_read_registers()
• Raw requests
  • send_raw_request(), receive_confirmation()
• Reply an exception
  • reply_exception()

Required methods

fn read_bits(
    &self,
    address: u16,
    num: u16,
    dest: &mut [u8]
) -> Result<u16, Error>

fn read_input_bits(
    &self,
    address: u16,
    num: u16,
    dest: &mut [u8]
) -> Result<u16, Error>

fn read_registers(
    &self,
    address: u16,
    num: u16,
    dest: &mut [u16]
) -> Result<u16, Error>

fn read_input_registers(
    &self,
    address: u16,
    num: u16,
    dest: &mut [u16]
) -> Result<u16, Error>

fn report_slave_id(
    &self,
    max_dest: usize,
    dest: &mut [u8]
) -> Result<u16, Error>

fn write_bit(&self, address: u16, status: bool) -> Result<(), Error>

fn write_bits(&self, address: u16, num: u16, src: &[u8]) -> Result<u16, Error>

fn write_register(&self, address: u16, value: u16) -> Result<(), Error>

fn write_registers(
    &self,
    address: u16,
    num: u16,
    src: &[u16]
) -> Result<u16, Error>

fn write_and_read_registers(
    &self,
    write_address: u16,
    write_num: u16,
    src: &[u16],
    read_address: u16,
    read_num: u16,
    dest: &mut [u16]
) -> Result<u16, Error>

fn mask_write_register(
    &self,
    address: u16,
    and_mask: u16,
    or_mask: u16
) -> Result<(), Error>

fn send_raw_request(
    &self,
    raw_request: &mut [u8],
    lenght: usize
) -> Result<u16, Error>

fn receive_confirmation(&self, response: &mut [u8]) -> Result<u16, Error>

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Implementors

impl ModbusClient for Modbus

fn read_bits(
    &self,
    address: u16,
    num: u16,
    dest: &mut [u8]
) -> Result<u16, Error>

read_bits - read many bits

The read_bits() function shall read the status of the num bits (coils) to the address of the remote device. The result of reading is stored in dest slice as unsigned bytes (8 bits) set to TRUE or FALSE.

The function uses the Modbus function code 0x01 (read coil status).

Return value

The function returns a Result containing the number of read bits if successful. Otherwise it returns an Error.

Parameters

• address - address of the remote device
• num - number of coils to read
• dest - the result of the reading is stored here

Examples

use libmodbus::{Modbus, ModbusClient, ModbusTCP};
let modbus = Modbus::new_tcp("127.0.0.1", 1502).unwrap();
let mut dest = vec![0u8; 100];

assert!(modbus.read_bits(0, 1, &mut dest).is_ok());

fn read_input_bits(
    &self,
    address: u16,
    num: u16,
    dest: &mut [u8]
) -> Result<u16, Error>

read_input_bits - read many input bits

The read_input_bits() function shall read the content of the num input bits to the address of the remote device. The result of reading is stored in dest slice as unsigned bytes (8 bits) set to TRUE or FALSE.

The function uses the Modbus function code 0x02 (read input status).

Return value

The function returns a Result containing the number of read bits if successful. Otherwise it returns an Error.

Parameters

• address - address of the remote device
• num - number of input bits to read
• dest - the result of the reading is stored here

Examples

use libmodbus::{Modbus, ModbusClient, ModbusTCP};
let modbus = Modbus::new_tcp("127.0.0.1", 1502).unwrap();
let mut dest = vec![0u8; 100];

assert!(modbus.read_input_bits(0, 1, &mut dest).is_ok());

fn read_registers(
    &self,
    address: u16,
    num: u16,
    dest: &mut [u16]
) -> Result<u16, Error>

read_registers - read many registers

The read_registers() function shall read the content of the num holding registers to the address of the remote device. The result of reading is stored in dest slice as u16 word values.

The function uses the Modbus function code 0x03 (read holding registers).

Return value

The function returns a Result containing the number of read bits if successful. Otherwise it returns an Error.

Parameters

• address - address of the remote device
• num - number of holding registers to read
• dest - the result of the reading is stored here

Examples

use libmodbus::{Modbus, ModbusClient, ModbusTCP};
let modbus = Modbus::new_tcp("127.0.0.1", 1502).unwrap();
let mut dest = vec![0u16; 100];

assert!(modbus.read_registers(0, 1, &mut dest).is_ok());

fn read_input_registers(
    &self,
    address: u16,
    num: u16,
    dest: &mut [u16]
) -> Result<u16, Error>

read_input_registers - read many input registers

The read_input_registers() function shall read the content of the num holding registers to the address of the remote device. The result of reading is stored in dest slice as u16 word values.

The function uses the Modbus function code 0x04 (read input registers). The holding registers and input registers have different historical meaning, but nowadays it’s more common to use holding registers only.

Return value

The function returns a Result containing the number of read bits if successful. Otherwise it returns an Error.

Parameters

• address - address of the remote device
• num - number of input registers to read
• dest - the result of the reading is stored here

Examples

use libmodbus::{Modbus, ModbusClient, ModbusTCP};
let modbus = Modbus::new_tcp("127.0.0.1", 1502).unwrap();
let mut dest = vec![0u16; 100];

assert!(modbus.read_input_registers(0, 1, &mut dest).is_ok());

fn report_slave_id(
    &self,
    max_dest: usize,
    dest: &mut [u8]
) -> Result<u16, Error>

report_slave_id - returns a description of the controller

The report_slave_id() function shall send a request to the controller to obtain a description of the controller. The response stored in dest contains: * the slave ID, this unique ID is in reality not unique at all so it's not possible to depend on it to know how the information are packed in the response. * the run indicator status (0x00 = OFF, 0xFF = ON) * additional data specific to each controller. For example, libmodbus returns the version of the library as a string.

Return value

The function returns a Result containing the number of read bits if successful. If the output was truncated due the max_dest limit then the return value is the number of bytes which would have been written to dest. Thus, a return value greater than the max_dest means that the resonse data was truncated. Otherwise the Result contains an Error.

Parameters

• max_dest - limit, write max_dest bytes from the response to dest
• dest - the result of the reading is stored here

Examples

use libmodbus::{Modbus, ModbusClient, ModbusTCP};
let modbus = Modbus::new_tcp("127.0.0.1", 1502).unwrap();
let mut bytes = vec![0u8; Modbus::MAX_PDU_LENGTH];

assert!(modbus.report_slave_id(Modbus::MAX_PDU_LENGTH, &mut bytes).is_ok());
// assert_eq!(bytes, vec![180, 255, 76, 77, 66, 51, 46, 49, 46, 52]));

fn write_bit(&self, address: u16, status: bool) -> Result<(), Error>

write_bit - write a single bit

The write_bit() function shall write the status at the address of the remote device. The value must be set to true of false.

The function uses the Modbus function code 0x05 (force single coil).

Return value

The function return an OK Result, containing a one, if successful. Otherwise it contains an Error.

Parameters

• address - address of the remote device
• status - status that should write at the address addr

Examples

use libmodbus::{Modbus, ModbusClient, ModbusTCP};
let modbus = Modbus::new_tcp("127.0.0.1", 1502).unwrap();
let address = 1;

assert!(modbus.write_bit(address, true).is_ok());

fn write_register(&self, address: u16, value: u16) -> Result<(), Error>

write_register - write a single register

The write_register() function shall write the value of value holding registers at the address addr of the remote device.

The function uses the Modbus function code 0x06 (preset single register).

Return value

The function return an OK Result, containing a one, if successful. Otherwise it contains an Error.

Parameters

• address - address of the remote device
• value - vec with the value of the holding register which shall be written

Examples

use libmodbus::{Modbus, ModbusClient, ModbusTCP};
let modbus = Modbus::new_tcp("127.0.0.1", 1502).unwrap();
let address = 1;
let value = u16::max_value();

assert!(modbus.write_register(address, value).is_ok());

fn write_bits(&self, address: u16, num: u16, src: &[u8]) -> Result<u16, Error>

write_bits - write many bits

The write_bits() function shall write the status of the bits (coils) from src at the address of the remote device. The src array must contains bytes set to TRUE or FALSE.

The function shall return the number of written bits if successful. Otherwise it contains an Error.

Return value

The function returns a Ok Result containing the number of written bits. Otherwise it contains an Error.

Parameters

• address - address of the remote device
• num - number or bits that should be writen at the address address
• src - vec of 0 and 1 (true and false) values

Examples

use libmodbus::{Modbus, ModbusClient, ModbusTCP};
let modbus = Modbus::new_tcp("127.0.0.1", 1502).unwrap();
let address = 1;
let tab_bytes = vec![0u8];

assert_eq!(modbus.write_bits(address, 1, &tab_bytes).unwrap(), 1);

fn write_registers(
    &self,
    address: u16,
    num: u16,
    src: &[u16]
) -> Result<u16, Error>

write_registers - write many registers

The write_registers() function shall write the content of the num holding registers from the array src at address of the remote device.

The function uses the Modbus function code 0x10 (preset multiple registers).

Return value

The function returns a Ok Result containing the number of written bytes. Otherwise it contains an Error.

Parameters

• address - address of the remote device
• num - number of holding registers that should write at the address address
• src - holding register

Examples

use libmodbus::{Modbus, ModbusClient, ModbusTCP};
let modbus = Modbus::new_tcp("127.0.0.1", 1502).unwrap();
let address = 1;
let tab_bytes = vec![0u16];

assert_eq!(modbus.write_registers(address, 1, &tab_bytes).unwrap(), 1);

fn write_and_read_registers(
    &self,
    write_address: u16,
    write_num: u16,
    src: &[u16],
    read_address: u16,
    read_num: u16,
    dest: &mut [u16]
) -> Result<u16, Error>

write_and_read_registers - write and read many registers in a single transaction

The write_and_read_registers() function shall write the content of the write_nb holding registers from the array src to the address write_addr of the remote device then shall read the content of the read_nb holding registers to the address read_addr of the remote device. The result of reading is stored in dest array as word values (16 bits).

The function uses the Modbus function code 0x17 (write/read registers).

Return value

The function returns a Ok Result containing the number of read registers. Otherwise it contains an Error.

Parameters

• write_address - address of the remote device
• write_num - number of holding registers
• src - holding register
• read_address - address of the remote device
• read_num - number of holding registers
• dest - holding register

Examples

use libmodbus::{Modbus, ModbusClient, ModbusTCP};
let modbus = Modbus::new_tcp("127.0.0.1", 1502).unwrap();
let address = 1;
let request_bytes = vec![1u16];
let mut response_bytes = vec![0u16];

assert_eq!(modbus.write_and_read_registers(
                address, 1, &request_bytes,
                address, 1, &mut response_bytes).unwrap(), 1);

fn mask_write_register(
    &self,
    address: u16,
    and_mask: u16,
    or_mask: u16
) -> Result<(), Error>

mask_write_register - mask a single register

The mask_write_register() function shall modify the value of the holding register at the address address of the remote device using the algorithm:

new value = (current value AND 'and') OR ('or' AND (NOT 'and'))

The function uses the Modbus function code 0x16 (mask single register).

Return value

The function returns a Ok Result if succesful. Otherwise it contains an Error.

Parameters

• address - address of the remote device
• and_mask - AND mask
• or_mask - OR mask

Examples

use libmodbus::{Modbus, ModbusClient, ModbusTCP};
let modbus = Modbus::new_tcp("127.0.0.1", 1502).unwrap();

assert!(modbus.mask_write_register(1, 0xF2, 0x25).is_ok());

fn send_raw_request(
    &self,
    raw_request: &mut [u8],
    lenght: usize
) -> Result<u16, Error>

send_raw_request - send a raw request

The send_raw_request() function shall send a request via the socket of the current modbus contest.

This function must be used for debugging purposes because you have to take care to make a valid request by hand. The function only adds to the message, the header or CRC of the selected backend, so raw_request must start and contain at least a slave/unit identifier and a function code. This function can be used to send request not handled by the library.

The enum FunctionCode provides a list of supported Modbus functions codes, to help build of raw requests.

Parameters

• raw_request - raw request to send
• length - raw request length

Return value

The function returns a Result, containing the full message lenght, counting the extra data relating to the backend, if successful. Otherwise it contains an Error.

Examples

use libmodbus::{Modbus, ModbusClient, ModbusTCP, FunctionCode};

let modbus = Modbus::new_tcp("127.0.0.1", 1502).unwrap();
let mut raw_request: Vec<u8> = vec![0xFF, FunctionCode::ReadHoldingRegisters as u8, 0x00, 0x01, 0x0, 0x05];
let mut response = vec![0u8; Modbus::TCP_MAX_ADU_LENGTH];
let request_len = raw_request.len();

assert_eq!(modbus.send_raw_request(&mut raw_request, request_len).unwrap(), 6);
assert!(modbus.receive_confirmation(&mut response).is_ok());

fn receive_confirmation(&self, response: &mut [u8]) -> Result<u16, Error>

receive_confirmation - receive a confirmation request

The receive_confirmation() function shall receive a request via the socket of the context ctx Member of the Modbus struct. This function must be used for debugging purposes because the received response isn’t checked against the initial request. This function can be used to receive request not handled by the library.

The maximum size of the response depends on the used backend, in RTU the response array must be Modbus::RTU_MAX_ADU_LENGTH bytes and in TCP it must be Modbus::TCP_MAX_ADU_LENGTH bytes. If you want to write code compatible with both, you can use the constant Modbus::MAX_ADU_LENGTH (maximum value of all libmodbus backends).

Return value

The function returns a Result containing the response length if successful. The returned request length can be zero if the indication request is ignored (eg. a query for another slave in RTU mode). Otherwise it contains an Error.

Parameters

• response - store for the received response

Examples

use libmodbus::{Modbus, ModbusClient, ModbusTCP};
let modbus = Modbus::new_tcp("127.0.0.1", 1502).unwrap();
let mut response = vec![0u8; Modbus::MAX_ADU_LENGTH];

assert!(modbus.receive_confirmation(&mut response).is_ok());

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