Modbus out - Modbus TCP output mailbox

The Modbus_out block transmits data over Ethernet using the Modbus TCP protocol on TCP port 502. The block can be configured to operate in one of two modes:

• Master/Client: the controller actively sends write requests to a remote Slave/Server device.
• Slave/Server: the controller updates its own internal registers, making the data available for an external Master/Client device to read.

The block supports the Register types listed below.

A concrete application example is presented in PN203, which runs a Modbus client on a TPI8032 and uses an external master on a computer.

To receive data, use the Modbus_in block instead. Alternatively, for periodic transfers without explicit requests, especially at higher rates or with numerous variables, the Ethernet UDP output mailbox can be used instead.

Parameters

• Mode: Selects the mailbox’s operating mode (Master/Client or Slave/Server).
• IP Address (Master mode only): Selects the IP address to whom the data will be sent.
• Type: Selects the Modbus register type to write to.
  • Discrete input (Slave mode only)
  • Coil
  • Input register (Slave mode only)
  • Holding register
• Start address: Sets the starting Modbus address for the range of registers to write (0–65535).
• Signal(s) type: Defines the data type of the input signal (int8, int16, int32, uint8, uint16, uint32, float32, or float64).
• Number of signals: Specifies the vector size of the data to be sent. The number of registers physically used is determined by the equivalent vector size in 16-bit words.
• Data transmission mode: Selects when the controller sends data.
  • On-demand: The user manually triggers each transmission via the trigger input (at the rising edge).
  • Periodically: The controller sends data at a fixed rate, regardless of whether the data has changed.
• Tx frequency (Hz): Defines the transmission rate in Hz (only relevant in Periodically mode).
• Endianness (Master mode only): Defines the order of the 16-bit registers used to encode multi-register values.
• Byte swap (Master mode only): When enabled, swaps the two bytes inside each 16-bit register.

The four combinations of Byte order and swap produce the following byte sequences, where A is the most significant byte of a 32-bit value and D the least significant:

Simulink block

Signal specification

• The data input accepts a vector containing the data to write via Modbus TCP. Use the Number of signals parameter to set the vector length, and the Signal(s) type parameter to set the input data type.
• The second input is the trigger (only visible in “on-demand” mode). The block sends data on a rising edge of this signal.

Mask

PLECS block

Signal specification

• The data input (D) accepts a vector containing the data to write via Modbus TCP. Use the Number of signals parameter to set the vector length, and the Signal(s) type parameter to set the input data type.
• The second input is the trigger (only visible in “on-demand” mode). The block sends data on a rising edge of this signal.

Mask

C++ functions

Master

bool ModbusMaster_ConfigureHoldingRegisterOutputMailbox(unsigned int mailboxId, const char* ip, uint16_t port, unsigned int modbusAddress, unsigned int size, tModbusRegByteOrder regByteOrder, float pollingFrequency);Code language: C++ (cpp)

bool ModbusMaster_ConfigureCoilOutputMailbox(unsigned int mailboxId, const char* ip, uint16_t port, unsigned int modbusAddress, unsigned int size, float pollingFrequency);Code language: C++ (cpp)

bool ModbusMaster_WriteHoldingRegister(unsigned int mailboxId, const void* data, unsigned int size);Code language: C++ (cpp)

bool ModbusMaster_WriteCoil(unsigned int mailboxId, const uint8_t* data, unsigned int size);Code language: C++ (cpp)

bool ModbusMaster_ConfigureRegisterMailboxEndianness(unsigned int mailboxId, tEndianness endianness, unsigned int bytesPerValue);Code language: C++ (cpp)

Slave

bool ModbusSlave_ConfigureHoldingRegisterOutputMailbox(unsigned int mailboxId, unsigned int modbusAddress, unsigned int size);Code language: C++ (cpp)

bool ModbusSlave_ConfigureInputRegisterOutputMailbox(unsigned int mailboxId, unsigned int modbusAddress, unsigned int size);Code language: C++ (cpp)

bool ModbusSlave_ConfigureCoilOutputMailbox(unsigned int mailboxId, unsigned int modbusAddress, unsigned int size);Code language: C++ (cpp)

bool ModbusSlave_ConfigureDiscreteInputOutputMailbox(unsigned int mailboxId, unsigned int modbusAddress, unsigned int size);Code language: C++ (cpp)

bool ModbusSlave_WriteHoldingRegister(unsigned int mailboxId, const void* data, unsigned int size);Code language: C++ (cpp)

bool ModbusSlave_WriteInputRegister(unsigned int mailboxId, const void* data, unsigned int size);Code language: C++ (cpp)

bool ModbusSlave_WriteCoil(unsigned int mailboxId, const uint8_t* data, unsigned int size);Code language: C++ (cpp)

bool ModbusSlave_WriteDiscreteInput(unsigned int mailboxId, const uint8_t* data, unsigned int size);Code language: C++ (cpp)