ModbusRtuSlave_PcCOM

ModbusRtuSlave_PcCOM 1:

The function block ModbusRtuSlave_PcCOM implements a Modbus slave that communicates via a serial PC interface (COM port). The function block ModbusRtuSlave_KL6x5B is available for communication via a serial Bus Terminal KL6001, KL6011 or KL6021.

The function block is passive until it receives telegrams from a connected Modbus master. A sample program explains the operating principle.

ModbusRtuSlave_PcCOM 2:

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 TC3 Serial Communication documentation.

ModbusRtuSlave_PcCOM 3: Inputs

VAR_INPUT
    UnitID          : UINT;
    AdrInputs       : POINTER TO BYTE; (* Pointer to the Modbus input area *)
    SizeInputBytes  : UINT;
    AdrOutputs      : POINTER TO BYTE; (* Pointer to the Modbus output area *)
    SizeOutputBytes : UINT;
    AdrMemory       : POINTER TO BYTE; (* Pointer to the Modbus memory area *)
    SizeMemoryBytes : UINT;
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.

AdrInputs

BYTE

Start address of the Modbus input area. The data area is usually declared as a PLC array, and the address can be calculated with ADR (input variable).

SizeInputBytes

UINT

Size of the Modbus input array in bytes. The size can be calculated with SIZEOF (input variable).

AdrOutputs

BYTE

Start address of the Modbus output area. The data area is usually declared as a PLC array, and the address can be calculated with ADR (output variable).

SizeOutputBytes

UINT

Size of the Modbus output array in bytes. The size can be calculated with SIZEOF (output variable).

AdrMemory

BYTE

Start address of the Modbus memory area. The data area is usually declared as a PLC array, and the address can be calculated with ADR (memory variable).

SizeMemoryBytes

UINT

Size of the Modbus memory array in bytes. The size can be calculated with SIZEOF (memory variable).

ModbusRtuSlave_PcCOM 4: Outputs

VAR_OUTPUT
    ErrorId : MODBUS_ERRORS;
END_VAR

Name

Type

Description

ErrorId

MODBUS_ERRORS

Indicates an error number in the event of disturbed or faulty communication.

Requirements

Development environment

Target platform

PLC libraries to include

TwinCAT v3.1.0

PC or CX (x86, x64, ARM)

Tc2_ModbusRTU