The Modbus TCP driver is an unVisiblee server component with the possibility to connect Modbus gateways.

Specification Modbus TCP

The Modbus protocol was originally developed by the company Modicon (today Schneider Electric) for the traffic with their controllers. Data was transmitted in the form of 16-bit registers (integer format) or as status information in the form of data bytes. Over time, the protocol has been continuously expanded. Modbus TCP is another type of communication.

The Modbus protocol is a single-master protocol. This master controls the entire transmission and monitors any timeouts that occur (no response from the addressed device). The connected devices may only send telegrams if requested by the master.

Modbus TCP is part of the IEC 61158 standard. A specification can be found at: http://www.modbus.org.

Get supported:

Modbus RTU (Serial), ASCII (Serial),

TCP, RTU over TCP, ASCII over TCP und UDP-IP (also Secure).

Note: When reading out several devices, there is a 100ms time delay between 2 devices.

Data points of the component

Name	Type	Function
Query cyclic - Autostart	Bidirectional	Here it is output whether the cyclic query is active. An off signal deactivates the cyclic query. Activated with an on signal.
Cyclic query - Pause [s]	Bidirectional	The set pause time between 2 queries is output here. If an integer value is sent to the data point, the pause time changes accordingly. This is possible, for example, with a touch value input.
Query once	Input	An ON signal at this input triggers a one-time query of the values. Each further on-signal triggers a further query.
Updating is carried out	Output	An on signal is output at this output for the duration of the update.
Diagnosis [Data]	Output	Output of the raw data for each read register.
Diagnosis [Text]	Output	Error texts are output here. These can be displayed e.g. with the component "Protocol window" .Attention: Diagnostic or debug outputs are only intended for error cases. Please use only with consultation of the support team! If used, these can significantly affect the performance of the service. If several drivers are available, the displays can be switchedvia the debugger.
Dynamic	Folder	The subfolders for unit, unit status, value and value (factor) are created in the Dynamic folder. Unit: Text from the "Unit" channel editor. Unitstatus: There are 3 data points per unit ID. Unit active for (de)activating the unit query, unit status for the output whether the unit can be read out (true) and unit warning, which outputs true if the query failed. Value: Data point for the created channel without offsetting with the factor. Value (factor): Data point for the created channel with offsetting of the factor.
Extended diagnostics	Input	The diagnostic output is extended via an on signal at this input. Attention: Diagnostic or debug outputs are only intended for error cases. Please use only with consultation of the support team! If used, they can significantly affect the performance of the service.
Faulty units	Output	Output of the unit ID as text that cannot be read out.
At least one value outside the range	Output	If limits have been entered for a value in the channel editor and this value is exceeded or not reached, an ON signal is output at this data point. Corresponding information is also output at the diagnostic output.
Ping Status	Output	In case of an IP connection, the connection of the device can be additionally checked via a ping check. An on signal shows if a connection exists.
Write cycle is being performed	Output	An on signal is output during the write cycle.
Write cycle time [ms]	Output	Output the time in milliseconds how long the write took.
Send once	Input	An ON signal at this input triggers a one-time sending of the values. Each further ON signal triggers a further transmission.
Send cyclically - Autostart	Bidirectional	This output shows whether cyclical transmission is active. An off signal deactivates cyclical transmission. Activated with an on signal.
Cyclical transmission - pause [s]	Bidirectional	The set pause time between 2 transmit telegrams is output here. If an integer value is sent to the data point, the pause time changes accordingly. This is possible, for example, with a touch value input.
Driver On/Off	Bidirectional	The driver is activated via an on signal. The preset state of the driver from the properties is output when the simulation or server is started.
Driver Gateway - MQTT Client	Bidirectional	Bidirectional communication interface between Modbus Master and MQTT Client. See Driver Gateway.
Driver Gateway - BACnet Server	Bidirectional	Bidirectionalcommunication interface between Modbus Master and BACnet Server. See Driver Gateway.
Driver Gateway - File Logger	Output	This data point can be connected to theDateilogger. This will transfer all data from the Modbus directly to Dateilogger.
Update time [ms]	Output	Outputs the time for a device update in milliseconds.
Connection - COM Port	Bidirectional	Here the COM port of the driver can be changed at runtime.
Connection - IP Address	Bidirectional	Here the IP address of the driver can be changed at runtime.
Connection status	Output	If the connection to the Modbus gateway is successful, an on signal is output.

Properties of the component

Name	Default	Function
Channels		The imported or manually created channels are listed here. These then appear as subfolders in the data point folder Dynamic. The description of the Modbus channel editor follows below.
Modbus Connection	Serial ...	The connection type to the Modbus device is set here (Com + IP-Adress).
Modbus Options	...	This is where you configure the Modbus connection options
Driver On/Off		Switch driver on or off.

Examples

- LAN-to-RS485 gateway

- Modbus TCP to M-Bus Connection

- Modbus TCP Wago 750 connection

In principle, it is possible to forward data from a Modbus master to a Modbus slave.
Here it is important that the two Modbus lines are clearly separated.

Here is a diagram to illustrate this:

ModbusMasterSlave

If a Modbus master is used in the EisBaer, the settings and registers in the instructions must be adopted from the Modbus slave.

If a Modbus slave is used in the EisBaer, you must check what the external Modbus master can do and which other slave devices are available on the Modbus line.

It is recommended that the device ID and the register addresses in the EisBaer slave are set uniquely.

This ensures that no two masters can access one slave. It also helps to better differentiate between the slave components.

In the diagram above, the black bar corresponds to the separation of the two systems. The data points of the driver components are linked 1:1.

Note on the TCP connection: in some cases the Modbus port 502 is blocked by the firewall.

Modbus in brief

A simple master/slave protocol (today also client/server): the master polls actively, the slave — the field device — answers.

Transport & addressing

- RTU and ASCII run over a serial line (RS-485, rarely RS-232), TCP and UDP over Ethernet/IP (port 502) — the content is identical, only the transport differs.

- RTU/ASCII over TCP or UDP: for serial servers / RS485-Ethernet gateways — the same framing, only the transport runs over the network instead of a COM port.

- Modbus/TCP Security: TCP connections can optionally be established TLS-encrypted.

- Unit ID: with RTU the unique device address 1–247, with TCP often 1 or 255.

- Register = 16 bits (one “word”). Larger values span several registers: 32-bit (Int32/Float32) = 2, 64-bit = 4 registers.

- Byte/word order: ABCD is the Modbus standard (big-endian); CDAB (word swap) is common on many PLCs for floats. Wrong order → nonsense values. The Decoder helps you find the right one.

The four data areas

- Coils (FC01): individual, writable bits — e.g. relays.

- Discrete Inputs (FC02): individual, read-only bits — e.g. switch states.

- Holding Registers (FC03): 16-bit registers, read & write — set points, parameters.

- Input Registers (FC04): 16-bit registers, read-only — measured values.

Funktionscodes

Function code	Name	Type	Description
FC01	Read Coils	Read	Read several coils (writable bits).
FC02	Read Discrete Inputs	Read	Read several input bits (read-only).
FC03	Read Holding Registers	Read	Read holding registers — the most common read code.
FC04	Read Input Registers	Read	Read input registers (measured values).
FC05	Write Single Coil	Write	Set or clear a single bit.
FC06	Write Single Register	Write	Write a single 16-bit register.
FC15	Write Multiple Coils	Write	Write several coils in one telegram.
FC16	Write Multiple Registers	Write	Write several registers in one telegram — e.g. a 32-bit value across 2 registers.
FC23	Read/Write Multiple	Both	ead and write in a single telegram (saves one round trip).
FC43	Read Device Identification	Read	Read vendor, product name and version as plain text.

Modbus Master

Modbus Master

Examples

Modbus in brief