RUTX08 Modbus

Main Page > RUTX Routers > RUTX08 > RUTX08 Manual > RUTX08 WebUI > RUTX08 Services section > RUTX08 Modbus

The information in this page is updated in accordance with firmware version RUTX_R_00.07.00.

SummaryEdit

Modbus is a serial communications protocol. Simple and robust, it has become a de facto standard communication protocol and is now a commonly available means of connecting industrial electronic devices.

This manual page provides an overview of the Modbus functionality in RUTX08 devices.


If you're having trouble finding this page or some of the parameters described here on your device's WebUI, you should turn on "Advanced WebUI" mode. You can do that by clicking the "Basic" button under "Mode", which is located at the top-right corner of the WebUI.

Networking rutx manual webui basic advanced mode.gif

Modbus TCP slaveEdit

A Modbus TCP slave listens for connections from a master (client) and sends out a response or sets some system related parameter in accordance with the given query. This provides the user with the possibility to set or get system parameters.

The figure below is an example of the Modbus TCP window section and the table below provides information on the fields contained in that window:

Networking rutos manual modbus modbus tcp slave.png

Field Value Description
Enable off | on; default: off Turns Modbus TCP on or off.
Port integer [0..65535]; default: 502 TCP port used for Modbus communications.
Device ID integer [0..255]; default: 1 The device's Modbus slave ID. When set to 0, it will respond to requests addressed to any ID.
Allow Remote Access off | on; default: off Allows remote Modbus connections by adding an exception to the device's firewall on the port specified in the field above.
Keep persistent connection off | on; default: off Allows keep the connection open after responding a Modbus TCP master request.
Connection timeout integer; default: 0 Sets TCP timeout in seconds after which the connection is forcefully closed.
Enable custom register block off | on; default: off Allows the usage of custom register block.

Get ParametersEdit


Modbus parameters are held within registers. Each register contains 2 bytes of information. For simplification, the number of registers for storing numbers is 2 (4 bytes), while the number of registers for storing text information is 16 (32 bytes). The register numbers and corresponding system values are described in the table below:

required value register address register number number of registers representation
System uptime 1 2 2 32 bit unsigned integer
System hostname 7 8 16 Text
Router serial number 39 40 16 Text
LAN MAC address 55 56 16 Text
Router name 71 72 16 Text
Current WAN IP address 139 140 2 32 bit unsigned integer
Digital non-isolated input (4 PIN connector) 324 325 1 32 bit unsigned integer
Digital open collector output (4 PIN connector) 325 326 1 32 bit unsigned integer

Set ParametersEdit


The Modbus daemon can also set some device parameters.

value to set register address register value description
Reboot 206 1 Reboots the router
Switch PIN 4 state 325 1|0 Toggles PIN 4 ON or OFF, when output is selected

Modbus TCP MasterEdit

A Modbus Master device can request data from Modbus slaves. The Modbus TCP Master section is used to configure Modbus TCP slaves. By default, the slave list is empty. To add a new slave, click the 'Add' button

Networking rutos manual modbus modbus tcp master modbus tcp slave devices add button.png

After clicking 'Add' you will be redirected to the newly added slave's configuration page.

You can create a maximum of 10 slave configurations.

Slave Device ConfigurationEdit


The Slave Device Configuration section is used to configure the parameters of Modbus TCP slaves that the Master (this RUTX08 device) will be querying with requests. The figure below is an example of the Slave Device Configuration and the table below provides information on the fields contained in that section:

Networking rutos manual modbus modbus tcp master slave device configuration.png

Field Value Description
Enabled off | on; default: off Turns communication with the slave device on or off.
Name string; default: none Slave device's name, used for easier management purposes.
Slave ID integer [0..255]; default: none Slave ID. Each slave in a network is assigned a unique identifier ranging from 1 to 255. When the master requests data from a slave, the first byte it sends is the Slave ID. When set to 0, the slave will respond to requests addressed to any ID.
IP address ip; default: none Slave device's IP address.
Port integer [0..65535]; default: none Slave device's Modbus TCP port.
Period integer [1..86400]; default: 60 Interval at which requests are sent to the slave device.
Timeout integer [1..30]; default: 5 Maximum response wait time.

Requests ConfigurationEdit


A Modbus request is a way of obtaining data from Modbus slaves. The master sends a request to a slave specifying the function code to be performed. The slave then sends the requested data back to the Modbus master. You can create a maximum of 64 request configurations for each slave device.

The Request Configuration list is empty by default. To add a new Request Configuration loon to the Add New Instance section. Enter a custom name into the 'Name' field and click the 'Add' button:

Networking rutos manual modbus modbus tcp master requests configuration add new instance.png

The new Request Configuration should become visible in the list:

Networking rutos manual modbus modbus tcp master requests configuration.png

Field Value Description
Name string; default: Unnamed Name of this Request Configuration. Used for easier management purposes.
Data type 8bit INT | 8bit UINT | 16bit INT, high byte first | 16bit INT, low byte first | 16bit UINT, high byte first | 16bit UINT, low byte first | 32bit float, Byte order 1,2,3,4 | 32bit float, Byte order 4,3,2,1 | 32bit float, Byte order 2,1,4,3 | 32bit float, Byte order 3,4,1,2; default: 16bit INT, high byte first Defines how read data will be stored.
Function Read coils (1) | Read input coils (2) | Read holding registers (3) | Read input registers (4) | Set single coil (5) | Set single coil register (6) | Set multiple coils (15) | Set multiple holding registers (16); default: Read holding registers (3) Specifies the type of register being addressed by a Modbus request.
First Register integer [0..65535]; default: 1 First Modbus register from which data will be read.
Register Count / Values integer [1..2000]; default: 1 Number of Modbus registers that will be read during the request.
No Brackets off | on; default: off Removes the starting and ending brackets from the request (only for read requests).
Delete [ X ] - (interactive button) Deletes the request.
off/on slider off | on; default: off Turns the request on or off.

Additional note: by default the newly added Request Configurations are turned off. You can use the on/off slider to the right of the Request Configuration to turn it on:

Networking rutos manual modbus modbus tcp master requests configuration on off slider.png


After having configured a request, you should see a new 'Request Configuration Testing' section appear. It is used to check whether the configuration works correctly. Simply click the 'Test' button and a response should appear in the box below. A successful response to a test may look something like this:

Networking rutos manual modbus modbus tcp master requests configuration testing.png

Alarms ConfigurationEdit


Alarms are a way of setting up automated actions when some Modbus values meet user-defined conditions. When the Modbus TCP Master (this RUTX08 device) requests some information from a slave device it compares that data to with the parameters set in an Alarm Configuration. If the comparison meets the specified condition (more than, less than, equal to, not equal to), the Master performs a user-specified action, for example, a Modbus write request or switching the state of an output.

The figure below is an example of the Alarms Configuration list. To create a new Alarm, click the 'Add' button.

Networking rutos manual modbus modbus tcp master alarms configuration add button.png

After adding the Alarm you should be redirected to its configuration page which should look similar to this:

Networking rutos manual modbus modbus tcp master alarms configuration.png

Field Value Description
Enabled off | on; default: off Turns the alarm on or off.
Function code Read Coil Status (1) | Read Input Status (2) | Read Holding Registers (3) | Read Input Registers (4); default: Read Coil Status (1) Modbus function used for this alarm's Modbus request. The Modbus TCP Master (this RUTX08 device) perform this request as often as specified in the 'Period' field in Slave Device Configuration.
Register integer [1..65536]; default: none Number of the Modbus coil/input/holding-register/input-register to read from.
Condition More than | Less than | Equal to | Not Equal to; default: Equal to When a value is obtained it will be compared against the value specified in the following field. The comparison will be made in accordance with the condition specified in this field.
Value various; default: none The value against which the read data will be compared.
Value integer [0..65535]; default: none The value against which the read data will be compared.
Action frequency Every trigger | First trigger; default: Every trigger Describes how frequently the specified action will be taken.
Redundancy protection off | on; default: off Protection against executing a configured action too often.
Redundancy protection period integer [1..86400]; default: none Duration to activate redundancy protection for, measured in seconds. This field becomes visible only when 'Redundancy protection' is turned on.
Action MODBUS Write Request; default: MODBUS Write Request Action that will be taken if the condition is met. Possible actions:
  • Modbus Request - sends a Modbus Write request to a specified slave.
MODBUS Write Request: IP address ip | host; default: none Modbus slave's IP address.
MODBUS Write Request: Port integer [0..65535]; default: none Modbus slave's port.
MODBUS Write Request: Timeout integer [1..30]; default: 5 Maximum time to wait for a response.
MODBUS Write Request: ID integer [1..255]; default: none Modbus slave ID.
MODBUS Write Request: Modbus function Read Force Single Coil (5) | Preset Single Register (6) | Force Multiple Coils (15) | Force Multiple Registers (16); default: Force Single Coil (5) A function code specifies the type of register being addressed by a Modbus request.
MODBUS Write Request: First register integer [0..65535]; default: none Begins reading from the register specified in this field.
MODBUS Write Request: Values integer [0..65535]; default: none Register/Coil values to be written (multiple values must be separated by space character).


MQTT GatewayEdit

The MQTT Gateway function is used to transfer Modbus data (send requests, receive responses) over MQTT. When it is enabled, the device (this RUTX08) subscribes to a REQUEST topic and publishes on a RESPONSE topic on a specified MQTT broker. It translates received MQTT message payload to a Modbus request and relays it to the specified Modbus TCP slave.

When the MQTT Gateway receives a response from the slave, it translates it to an MQTT message and publishes it on the RESPONSE topic.

Networking rutos manual modbus mqtt gateway scheme.png

Below is an example of the MQTT Gateway page. Refer to the table for information on MQTT Gateway configuration fields.

Networking rutos manual modbus mqtt gateway.png

Field Value Description
Enable off | on; default: off Turns MQTT gateway on or off.
Host ip | host; default: 127.0.0.1 IP address or hostname of an MQTT broker.
Port integer [0..65535]; default: 1883 Port number of the MQTT broker.
Request topic alphanumeric string; default: request MQTT topic for sending requests.
Response topic alphanumeric string; default: response MQTT topic for subscribing to responses.
Username string; default: none Username for authentication to the MQTT broker.
Password string; default: none Password for authentication to the MQTT broker.

Request messagesEdit


Modbus request data sent in the MQTT payload should be generated in accordance with the following format:

0 <COOKIE> <IP_TYPE> <IP> <PORT> <TIMEOUT> <SLAVE_ID> <MODBUS_FUNCTION> <REGISTER_NUMBER> <REGISTER_COUNT/VALUE>

Explanation:

  • 0 - must be 0, which signifies a textual format (currently the only one implemented).
  • Cookie - a 64-bit unsigned integer in range [0..264]). A cookie is used in order to distinguish which response belongs to which request, each request and the corresponding response contain a matching cookie: a 64-bit unsigned integer.
  • IP type - host IP address type. Possible values:
    • 0 - IPv4 address;
    • 1 - IPv6 address;
    • 2 - hostname that will be resolved to an IP address.
  • IP - IP address of a Modbus TCP slave. IPv6 must be presented in full form (e.g., 2001:0db8:0000:0000:0000:8a2e:0370:7334).
  • Port - port number of the Modbus TCP slave.
  • Timeout - timeout for Modbus TCP connection, in seconds. Range [1..999].
  • Slave ID - Modbus TCP slave ID. Range [1..255].
  • Modbus function - Modbus task type that will be executed. Possible values are:
    • 3 - read holding registers;
    • 6 - write to a single holding register;
    • 16 - write to multiple holding registers.
  • Register number - number of the first register (in range [1..65536]) from which the registers will be read/written to.
  • Register count/value - this value depends on the Modbus function:
    • 3 - register count (in range [1..125]); must not exceed the boundary (first register number + register count <= 65537);
    • 6 - register value (in range [0..65535]);
    • 16 - register count (in range [1..123]); must not exceed the boundary (first register number + register count <= 65537); and register values separated with commas, without spaces (e.g., 1,2,3,654,21,789); there must be exactly as many values as specified (with register count); each value must be in the range of [0..65535].

Response messagesEdit


A special response message can take one of the following forms:

<COOKIE> OK                              - for functions 6 and 16
<COOKIE> OK <VALUE> <VALUE> <VALUE>...   - for function 3, where <VALUE> <VALUE> <VALUE>... are read register values
<COOKIE> ERROR: ...                      - for failures, where ... is the error description

ExamplesEdit


Below are a few examples of controlling/monitoring the internal Modbus TCP Slave on RUTX08.


Reboot the device

  • Request:
    0 65432 0 192.168.1.1 502 5 1 6 206 1
  • Response:
    65432 OK

Retrieve uptime

  • Request:
    0 65432 0 192.168.1.1 502 5 1 3 2 2
  • Response:
    65432 OK 0 5590

If you're using Eclipse Mosquitto (MQTT implementation used on RUTX08), Publish/Subscribe commands may look something like this:

Retrieve uptime

  • Request:
    mosquitto_pub -h 192.168.1.1 -p 1883 -t request -m "0 65432 0 192.168.1.1 502 5 1 3 2 2"
  • Response:
    mosquitto_sub -h 192.168.1.1 -p 1883 -t response
    65432 OK 0 5590

See alsoEdit