Modbus
MODBUS Library¶
To talk with a slave device an object of type ModbusTCP or ModbusSerial must be initialized, depending on what kind of communication is needed.
If serial communication is used, a device object that implements write, read and close methods is needed. The device object can be created with serial class.
When a connection with a slave device has been established, coils and registers can be accessed with the methods in each class.
ModbusTCP class¶
class ModbusTCP¶
ModbusTCP(identifier)
Create an instance of the ModbusTCP class which allow modbus communication with slave device using TCP.
identifier: The slave device identifier, used in the header of every packet.
method read_coils¶
read_coils(address, n)
address: The starting address n: the number of coils to read from address
Read the status of n coils, starting from address.
Returns: a python list containing the values of the coils.
method read_input¶
read_input(address, n)
address: The starting address n: the number of input register to read, starting from address
Returns: a python list containing the values of the input registers
method read_holding¶
read_holding(address, n)
address: The starting address n: the number of holding register to read, starting from address
Returns: a python list containing the values of the holding registers
method read_discrete¶
read_discrete(address, n)
address: The starting address n: the number of discrete register to read, starting from address
Returns: a python list containing the values of the discrete registers
method write_coil¶
write_coil(address, n)
address: the address of the coil value: the new value
Returns: 1 if the write has been successfull. Otherwhise an exception will be thrown
method write_register¶
write_register(address, n)
address: the address of the register value: the new value
Returns: 1 if the write has been successfull. Otherwhise an exception will be thrown
method write_multiple_registers¶
write_multiple_registers(address, n, values)
address: the address of the first holding register n: the number of registers value: a python list containing the new values
Returns: the number of holding registers written
method connect¶
connect(address, [port = 502])
address: the ip address of the slave device port: port on which the slave device is listening to
method close¶
close()
Closes the connection with the slave device
ModbusSerial class¶
class ModbusSerial¶
ModbusSerial(identifier, serial_device)
identifier The slave device identifier
serial_device an object representing the device. It must implement read, write and close methods to communicate with the serial port. See the serial class.
receive_timeout timeout on the receiving function;
receive_wait time to wait before reading from serial
method read_coils¶
read_coils(address, n)
address The starting address n the number of coils to read from address
Read the status of n coils, starting from address.
Returns: a python list containing the values of the coils.
method read_input¶
read_input(address, n)
address The starting address n the number of input register to read, starting from address
Returns: a python list containing the values of the input registers
method read_holding¶
read_holding(address, n)
address The starting address n the number of holding register to read, starting from address
Returns: a python list containing the values of the holding registers
method read_discrete¶
read_discrete(address, n)
address The starting address n the number of discrete register to read, starting from address
Returns: a python list containing the values of the discrete registers
method write_coil¶
write_coil(address, n)
address the address of the coil value the new value
Returns: 1 if the write has been successful. Otherwise an exception will be thrown
method write_register¶
write_register(address, n)
address the address of the register value the new value
Returns: 1 if the write has been successful. Otherwise an exception will be thrown
method write_multiple_coils¶
write_multiple_coils(address, n, values)
address the address of the first coil n the number of coils value a python list containing the new values
Returns: the number of coils written
method write_multiple_registers¶
write_multiple_registers(address, n, values)
address the address of the first holding register n the number of registers value a python list containing the new values
Returns: the number of holding registers written
method close¶
close()
Close the serial port by calling the close() function implemented by the device associated class.