ModbusRtuMaster_PcCOM

ModbusRtuMaster_PcCOM 1:

The function block ModbusRtuMaster_PcCOM implements a Modbus master that communicates via a serial PC interface (COM port). The function block ModbusRtuMaster_KL6x5B is available for communication via a serial Bus Terminal KL6001, KL6011 or KL6021.

Hardware connection

The data structures required for the link with the communication port are included in the function block. They are displayed in the TwinCAT System Manager once the PLC program has been integrated and can be connected with a COM port. The procedure is analogous to the description in the chapter Serial PC Interface of the TF6340 TwinCAT 3 Serial Communication documentation.

The function block is not called in its basic form, but individual actions of that block are used within a PLC program. Each Modbus function is implemented as an action.

Supported Modbus functions (actions)

ModbusMaster.ReadCoils
Modbus function 1 = Read Coils
Reads binary outputs (coils) from a connected slave. The data is stored in compressed form (8 bits per byte) from the specified address pMemoryAddr.
ModbusMaster.ReadInputStatus
Modbus function 2 = Read Input Status
Reads binary inputs from a connected slave. The data is stored in compressed form (8 bits per byte) from the specified address pMemoryAddr.
ModbusMaster.ReadRegs
Modbus function 3 = Read Holding Registers
Reads data from a connected slave.
ModbusMaster.ReadInputRegs
Modbus function 4 = Read Input Registers
Reads input registers from a connected slave.
ModbusMaster.WriteSingleCoil
Modbus function 5 = Write Single Coil
Sends a binary output (coil) to a connected slave. The data must be ready to send in compressed form (8 bits per byte) from the specified address pMemoryAddr.
ModbusMaster.WriteSingleRegister
Modbus function 6 = Write Single Register
Sends a single data word to a connected slave
ModbusMaster.WriteMultipleCoils
Modbus function 15 = Write Multiple Coils
Sends binary outputs (coils) to a connected slave. The data must be ready to send in compressed form (8 bits per byte) from the specified address pMemoryAddr.
ModbusMaster.WriteRegs
Modbus function 16 = Preset Multiple Registers
Sends data to a connected slave
ModbusMaster.Diagnostics
Modbus function 8 = Diagnostics
Sends a diagnostic request to the slave with a user-specified function code (subfunction code). Since this function does not address a memory, the function code is transferred in the data word MBAddr. Any data required for the function is included in pMemoryAddr.

Inputs

VAR_INPUT
    UnitID      : UINT;
    Quantity    : WORD;
    MBAddr      : WORD;
    cbLength    : UINT;
    pMemoryAddr : POINTER TO BYTE;
    Execute     : BOOL;
    Timeout     : TIME;
END_VAR

Name	Type	Description
UnitID	UINT	Modbus station address (1..247). The Modbus slave will only answer if it receives telegrams containing its own station address. Optionally, collective addresses can be used for replying to any requests. Address 0 is reserved for broadcast telegrams and is therefore not a valid station address (see UnitID)
Quantity	WORD	Number of data words to be read or written for word-oriented Modbus functions. For bit-oriented Modbus functions, Quantity specifies the number of bits (inputs or coils).
MBAddr	WORD	Modbus data address, from which the data are read from the end device (slave). This address is transferred unchanged to the slave and is interpreted there as data address. With the Diagnostics function (8) the function code (subfunction code) is transferred here.
cbLength	UINT	Size of the data variable used for send or read actions in bytes. cbLength must be greater than or equal to the amount of data transferred as determined by Quantity. For word accesses, for example: [cbLength >= Quantity 2]. cbLength* can be calculated with SIZEOF(Modbus data).
pMemoryAddr	BYTE	Memory address in the PLC, calculated with ADR (Modbus data). For read actions, the read data are stored in the addressed variable. For send actions, the data are transferred from the addressed variable to the end device.
Execute	BOOL	Start signal. The action is triggered by a rising edge at the Execute input.
Timeout	TIME	Timeout value for waiting for a response from the addressed slave.

Outputs

VAR_OUTPUT
    BUSY    : BOOL;
    Error   : BOOL;
    ErrorId : MODBUS_ERRORS;
    cbRead  : UINT;
END_VAR

Name	Type	Description
Busy	BOOL	Indicates that the function block is active. Busy becomes TRUE with a rising edge at Execute and becomes FALSE again once the started action is completed. At any one time, only one action can be active.
Error	BOOL	Indicates that an error occurred during execution of an action.
ErrorId	MODBUS_ERRORS	Indicates an error number in the event of disturbed or faulty communication.
cbRead	UINT	Provides the number of read data bytes for a read action.

Requirements

Development environment	Target platform	PLC libraries to include
TwinCAT v3.1.0	PC or CX (x86, x64, Arm®)	Tc2_ModbusRTU