Modbus TCP

The Modbus protocol (standard IEC 61158) is a protocol for data exchange between a Modbus server and a Modbus client. Port 502 is reserved for Modbus TCP. The following data can be read or written:

Data type	Unit	Access
Digital outputs	[Bit]	Reading & Writing
Digital inputs	[Bit]	Read
Analog inputs	[16Bit]	Read
Analog inputs/outputs	[16Bit]	Reading & Writing

The following Modbus functions are implemented:

Number	Name	Server	Client	Description
FC1	Read Coils	Yes	Yes	read back several digital outputs
FC2	Read Discrete Inputs	Yes	Yes	read multiple digital inputs
FC3	Read Holding Register	Yes	Yes	read multiple analog inputs/outputs
FC4	Read Input Register	Yes	Yes	read multiple analog inputs/outputs
FC5	Write Single Coil	Yes	No	set a digital output
FC6	Write Single Register	Yes	No	write an analog output
FC15	Write Multiple Coils	Yes	Yes	set several digital outputs
FC16	Write Multiple Registers	Yes	Yes	Write multiple analog outputs
FC23	Read/Write Multiple Registers	No	Yes	write several analog outputs and read inputs/outputs simultaneously

Modbus TCP Server

In the Gefasoft Modbus TCP server, data blocks are created that can be read and written by a Modbus TCP client. Each data block must have a unique address range consisting of start address and data length. The unit of the start address or the data length depends on the data type. Digital inputs/outputs are addressed in [Bit] and analog inputs/outputs in [16Bit] or [WORD]. The data ranges of the digital inputs/outputs and analog inputs/outputs must not overlap!

1. Type: Modbus TCP Server

2. ID: ID assigned

3. name suffix: Name control

4. Create: Press button to generate object

5. DisplayName: Name controller

6. IP/Port: Enter the IP address and port for the Modbus TCP Server Listener.

7. UnitIdentifier: The Gefasoft Modbus server ignores the UnitIdentifier received from the client. Since there is only one unit, all unit identifiers are accepted. The data block is identified by the start address received from the client.

8. +: Adding data areas to be used for communication

1. DataBlockID: ID for this data block.

2. Name: Name of the data area

3. Count: Data count in [Bit] for digital inputs/outputs, or in [16Bit] for analog inputs/outputs.

4. EType: Data type

Data type	Unit	Impement	Client access
EDigitalInputs	[Bit]	Yes	digital [Bit] & analog [16Bit] Read
EDigitalOutputs	[Bit]	Yes	digital [Bit] & analog [16Bit] read & write
EHoldingRegisters	[16Bit]	Yes	digital [Bit] & analog [16Bit] read & write
EInputRegisters	[16Bit]	Yes	digital [Bit] & analog [16Bit] Read
EOutputRegisters	[16Bit]	Yes	digital [Bit] & analog [16Bit] read & write
EInputRegistersAcyclic	[16Bit]	No	none

Hint

Since the Viper Modbus TCP Server keeps the process data in the main memory, access to all implemented data block types is possible via analog [16Bit] and digital [1Bit] Modbus functions.

5. StartAddress: Start address of the data in [Bit] for digital inputs/outputs, or in [16Bit] for analog inputs/outputs.

6. TwistRegisterBytes: Swap high and low bytes during register access (for analog inputs/outputs).

7. Acyclic input registers: The Gefasoft Modbus server does not implement acyclic register access. All data is stored in the process image in memory and is read and written directly.

8. FileName: Path to a file to permanently save the data of the data block. The data is saved on exit and read again on startup.

See also

Modbus TCP

Modbus TCP Client

The Gefasoft TCP client is used to exchange data with a Modbus TCP server.

1. Type: Modbus TCP Client

2. ID: ID assigned

3. name suffix: Name control

4. Create: Press button to generate GInOut-Hardwar

5. DisplayName: Name controller

6. IP/Port: Enter the IP address and the port of the Modbus TCP server to which the client should connect.

7. UnitIdentifier: Unit ID for all data queried by the server (The UnitIdentifier is part of the Modbus header).

8. +: Adding data areas to be used for communication

1. DataBlockID: ID for this data block.

2. Name: Name of the data area

3. Count: Data count in [Bit] for digital inputs/outputs, or in [16Bit] for analog inputs/outputs.

4. EType: Data type

Type	Unit	Implement
EDigitalInputs	[Bit]	Yes
EDigitalOutputs	[Bit]	Yes
EHoldingRegisters	[16Bit]	Yes
EInputRegisters	[16Bit]	Yes
EOutputRegisters	[16Bit]	Yes
EInputRegistersAcyclic	[16Bit]	Yes

5. StartAddress: Start address of the data in [Bit] for digital inputs/outputs, or in [16Bit] for analog inputs/outputs.

6. TwistRegisterBytes: Swap high and low bytes during register access (for analog inputs/outputs).

7. Acyclic input registers: Some analog data are not located in the process image of the Modbus server. These must then be read out via EInputRegistersAcyclic (FC23). The Modbus server is informed via the parameters ‘ReadAcyclStartAddressWrite = target address for register number’ and ‘ReadAcyclDataWrite = register number to be read’ which process data it should send to the client.

Hint

For analog outputs (registers), the data alignment must be set to two bytes, since the unit for transmitting the data in the Modbus protocol is [16Bit] !

Double-clicking the data node (1) opens the parameter dialog for the data settings. The parameter alignment (2) must be set to ‘2’. Also in the data editor (3) the data can then only ever be written 16bit by 16bit.

See also

Modbus TCP

Hint

With some Modbus TCP bus controllers it is necessary to switch off the watchdog on the server side, otherwise no error-free communication with the GInOut Modbus TCP client is possible.

Disable the watchdog of the bus controller B&R X20BC0087.

1. Start cmd.exe

2. enter the following commands:

• telnet 192.168.100.1

• fc6 0x1043 0xC0

• flash store

• quit

Disable the watchdog of the Beckhoff BK9100 bus controller.

1. Create Modbus TCP Client in the HW Explorer (172.16.17.1:502).

2. Create data block holding register address 4384 (0x1120). This is the register for the watchdog time [ms].

3. Create GInOut data for the data block and write the value ‘0’ into register 4384 (0x1120).