RUT955 Modbus

Main Page > RUT Routers > RUT955 > RUT955 Manual > RUT955 WebUI > RUT955 Services section > RUT955 Modbus

The information in this page is updated in accordance with firmware version RUT9_R_00.07.04.5.
Note: click here for the old style WebUI (FW version RUT9XX_R_00.06.09.5 and earlier) user manual page.

Summary

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 RUT955 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 rut9 manual webui basic advanced mode.gif

Modbus TCP Slave

A Modbus TCP Slave listens for connections from a TCP 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 v2.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.
Mobile Data type Bytes | Kilobytes | Megabytes; default: Bytes Selects mobile data unit representation type.
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: onn Allows keep the connection open after responding a Modbus TCP master request.
Connection timeout integer [0..60]; 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.
Register file path path; default: /tmp/regfile Path to file in which the custom register block will be stored. Files inside /tmp or /var are stored in RAM. They vanish after reboot, but do not degrade flash memory. Files elsewhere are stored in flash memory. They remain after reboot, but degrade flash memory (severely, if operations are frequent).
First register number integer [1025..65536]; default: 1025 First register in custom register block
Register count integer [1..64512]; default: 128 Register count in custom register block

Modbus Serial Slave

A Modbus Serial Slave listens for connections from a serial 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.

Modbus Serial Slave Configuration


The Modbus Serial Slave Configuration section is used to configure serial slaves. By default, the list is empty. To add a new slave instance, enter the instance name, select serial interface and click the 'Add' button.

Networking rutos manual modbus modbus serial slave add button rs232 1 v1.png

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

Networking rutos manual modbus modbus serial slave configuration rs232 1 v1.png

Field Value Description
Enable off | on; default: off Enables this Modbus Serial Slave instance configuration.
Name string; default: none Name of the serial slave instance. Used for management purposes only.
Device RS232 | RS485 | USB RS232 interface; default: RS232 Specifies which serial port will be used for serial communication.
Device ID integer [0..255]; default: 1 Specifies which serial port will be used for serial communication.
Baud rate 300 | 1200 | 2400 | 4800 | 9600 | 19200 | 38400 | 57600 | 115200| 230400 | 460800 | 921600 | 1000000 | 3000000; default: 9600 Serial data transmission rate (in bits per second).
Data bits 5 | 6 | 7 |8; default: 8 Number of data bits for each character.
Stop bits 1| 2; default: 1 Stop bits sent at the end of every character allow the receiving signal hardware to detect the end of a character and to resynchronise with the character stream. Electronic devices usually use one stop bit. Two stop bits are required if slow electromechanical devices are used.
Parity Even | Odd| Mark | Space | None; default: None In serial transmission, parity is a method of detecting errors. An extra data bit is sent with each data character, arranged so that the number of 1 bits in each character, including the parity bit, is always odd or always even. If a byte is received with the wrong number of 1s, then it must have been corrupted. However, an even number of errors can pass the parity check.
  • None (N) - no parity method is used.
  • Odd (O) - the parity bit is set so that the number of "logical ones (1s)" has to be odd.
  • Even (E) - the parity bit is set so that the number of "logical ones (1s)" has to be even.
  • Space (s) - the parity bit will always be a binary 0.
  • Mark (M) - the parity bit will always be a binary 1.
Flow control None | RTS/CTS | Xon/Xoff; default: None In many circumstances a transmitter might be able to send data faster than the receiver is able to process it. To cope with this, serial lines often incorporate a "handshaking" method, usually distinguished between hardware and software handshaking.
  • RTS/CTS - hardware handshaking. RTS and CTS are turned OFF and ON from alternate ends to control data flow, for instance when a buffer is almost full.
  • Xon/Xoff - software handshaking. The Xon and Xoff characters are sent by the receiver to the sender to control when the sender will send data, i.e., these characters go in the opposite direction to the data being sent. The circuit starts in the "sending allowed" state. When the receiver's buffers approach capacity, the receiver sends the Xoff character to tell the sender to stop sending data. Later, after the receiver has emptied its buffers, it sends an Xon character to tell the sender to resume transmission.
RS485: Full Duplex off | on; default: off Enables RS485 full duplex.
Enable custom register block off | on; default: off Allows the usage of custom register block.
Register file path path; default: /tmp/regfile Path to file in which the custom register block will be stored. Files inside /tmp or /var are stored in RAM. They vanish after reboot, but do not degrade flash memory. Files elsewhere are stored in flash memory. They remain after reboot, but degrade flash memory (severely, if operations are frequent).
First register number integer [1025..65536]; default: 1025 First register in custom register block
Register count integer [1..64512]; default: 128 Path to file in which the custom register block will be stored. Files inside /tmp or /var are stored in RAM. They vanish after reboot, but do not degrade flash memory. Files elsewhere are stored in flash memory. They remain after reboot, but degrade flash memory (severely, if operations are frequent).

Modbus Registers

Get Parameters


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
Mobile signal strength (RSSI in dBm) 3 4 2 32 bit integer
System temperature (in 0.1 °C) 5 6 2 32 bit integer
System hostname 7 8 16 Text
GSM operator name 23 24 16 Text
Router serial number 39 40 16 Text
LAN MAC address 55 56 16 Text
Router name 71 72 16 Text
Currently active SIM card slot 87 88 16 Text
Network registration info 103 104 16 Text
Network type 119 120 16 Text
Digital input (DIN1) state 135 136 2 32 bit integer
Digital galvanically isolated input (DIN2) state 137 138 2 32 bit integer
Current WAN IP address 139 140 2 8 bit unsigned integer
Analog input (PIN 9) value 141 142 2 32 bit unsigned integer
GPS latitude coordinate 143 144 2 32 bit float
GPS longitude coordinate 145 146 2 32 bit float
GPS fix time 147 148 16 Text (Unix timestamp×1000)
GPS date and time 163 164 16 Text (DDMMYYhhmmss)
GPS speed 179 180 2 32 bit float
GPS satellite count 181 182 2 32 bit unsigned integer
GPS accuracy 183 184 2 32 bit float
Mobile data received today (SIM1) 185 186 2 32 bit unsigned integer
Mobile data sent today (SIM1) 187 188 2 32 bit unsigned integer
Mobile data received this week (SIM1) 189 190 2 32 bit unsigned integer
Mobile data sent this week (SIM1) 191 192 2 32 bit unsigned integer
Mobile data received this month (SIM1) 193 194 2 32 bit unsigned integer
Mobile data sent this month (SIM1) 195 196 2 32 bit unsigned integer
Mobile data received last 24h (SIM1) 197 198 2 32 bit unsigned integer
Mobile data sent last 24h (SIM1) 199 200 2 32 bit unsigned integer
Galvanically isolated open collector output status 201 202 1 16 bit unsigned integer
Relay output status 202 203 1 16 bit unsigned integer
Active SIM card 205 206 1 16 bit unsigned integer
Mobile data received last week (SIM1) 292 293 2 32 bit unsigned integer
Mobile data sent last week (SIM1) 294 295 2 32 bit unsigned integer
Mobile data received last month (SIM1) 296 297 2 32 bit unsigned integer
Mobile data sent last month (SIM1) 298 299 2 32 bit unsigned integer
Mobile data received today (SIM2) 300 301 2 32 bit unsigned integer
Mobile data sent today (SIM2) 302 303 2 32 bit unsigned integer
Mobile data received this week (SIM2) 304 305 2 32 bit unsigned integer
Mobile data sent this week (SIM2) 306 307 2 32 bit unsigned integer
Mobile data received this month (SIM2) 308 309 2 32 bit unsigned integer
Mobile data sent this month (SIM2) 310 311 2 32 bit unsigned integer
Mobile data received last 24h (SIM2) 312 313 2 32 bit unsigned integer
Mobile data sent last 24h (SIM2) 314 315 2 32 bit unsigned integer
Mobile data received last week (SIM2) 316 317 2 32 bit unsigned integer
Mobile data sent last week (SIM2) 318 319 2 32 bit unsigned integer
Mobile data received last month(SIM2) 320 321 2 32 bit unsigned integer
Mobile data sent last month (SIM2) 322 323 2 32 bit unsigned integer
Digital non-isolated input 324 325 1 16 bit unsigned integer
Digital open collector output 325 326 1 16 bit unsigned integer
Modem ID 328 329 8 Text
ACL activity 345 346 1 16 bit unsigned integer
ACL status 346 347 2 32 bit float
IMSI 348 349 16 Text
Unix timestamp 364 365 2 32 bit unsigned integer
Local ISO time 366 367 12 Text
UTC time 378 389 12 Text
LAN IP 394 395 2 8 bit unsigned integer
Add SMS 397 398 90 Text

Set Parameters


The Modbus daemon can also set some device parameters.

value to set register address register number register value description
Hostname 7 8 Hostname (in decimal form) Changes hostname
Device name 71 72 Device name (in decimal form) Changes device name
Galvanically isolated open collector output status 201 202 1 | 0 Toggles DOUT1 ON or OFF
Relay output status 202 203 1 | 0 Toggles DOUT2 ON or OFF
Switch WiFi ON/OFF 203 204 1 | 0 Turns WiFi ON or OFF
Switch mobile data connection (ON/OFF*) 204 205 1 | 0 Turns mobile data connection ON or OFF
Switch SIM card 205 206 1 | 2 | 0 Changes the active SIM card slot
  • 1 - switch to SIM1
  • 2 - switch to SIM2
  • 0 - switch from the the SIM card opposite of the one currently in use (SIM1 → SIM2 or SIM2 → SIM1)
Reboot 206 207 1 Reboots the router
Change APN 207 208 APN code Changes APN.
The number of input registers may vary depending on the length of the APN, but the very first byte of the set APN command denotes the number of the SIM card for which to set the APN. This byte should be set to:
  • 1 - to set APN for SIM1
  • 2 - to set APN for SIM2
Switch PIN 4 state 325 326 1|0 Toggles PIN 4 ON or OFF
Switch ACL activity 345 346 1|0 Turns ACL activity ON or OFF
Switch 2.4GHz WiFi ON/OFF 390 391 1 | 0 Turns 2.4GHz WiFi ON or OFF
Change LAN IP 394 395 IPv4 (in decimal form) Changes device LAN IP
Send SMS 396 397 1|0 Sends an SMS with content defined in Add SMS (397) register
Add SMS 397 398 Message (in decimal form) Define SMS content which will be sent using Send SMS (396) register.
The register array is split into two parts that represent the recipient's "phone number" (first 10 registers) and the "SMS message contents" (remaining 80 registers).

Modbus TCP Master

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.

Slave Device Configuration


The Slave Device Configuration section is used to configure the parameters of Modbus TCP slaves that the Master (this RUT955 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 v2.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 ip4; 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.
Always reconnect off | on; default: off Create new connection after every Modbus request.
Number of timeouts integer [0..10]; default: 1 Skip pending request and reset connection after number of request failures.
Frequency Period | Schedule; default: Period
Delay integer [0..999]; default: 0 Wait in milliseconds after connection initialization.
Period integer [1..99999]; default: none Interval in seconds for sending requests to this device

Requests Configuration


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.

Note: Modbus TCP Master uses Register Number instead of Register Address for pointing to a register. For example, to request the Uptime of a device, you must use 2 in the First Register field.

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 v1.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 (various Byte order) | 32bit INT (various Byte order) | 32bit UINT (various Byte order) | ASCII | Hex | Bool; 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.
Remove Brackets off | on; default: off Removes the starting and ending brackets from the request (only for read requests).
off/on slider off | on; default: off Turns the request on or off.
Delete [ X ] - (interactive button) Deletes the request.

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 Configuration


Alarms are a way of setting up automated actions when some Modbus values meet user-defined conditions. When the Modbus TCP Master (this RUT955 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 v1.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 RUT955 device) perform this request as often as specified in the 'Period' field in Slave Device Configuration.
Compared condition 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 (various Byte order) | 32bit INT (various Byte order) | 32bit UINT (various Byte order) | ASCII | Hex | Bool; default: 16bit INT, high byte first Select data type that will be used for checking conditions.
First register number integer [1..65536]; default: none Number of the Modbus coil/input/holding-register/input-register to read from.
Values various; default: none The value against which the read data will be compared.
Condition More than | Less than | Equal to | Not Equal to | Less or equal | More or equal; default: More than 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.
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 SMS | MODBUS Write Request| Trigger output | MQTT message; default: MODBUS Write Request Action that will be taken if the condition is met. Possible actions:
  • SMS - sends and SMS message to a specified recipient(s).
  • Modbus Request - sends a Modbus Write request to a specified slave.
  • Trigger output - changes state of selected I/O output pin.
SMS: Message string; default: none SMS message text.
SMS: Phone number phone number; default: none Recipient's phone number.
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 Set Single Coil (5) | Set Single Register (6) | Set Multiple Coils (15) | Set Multiple Registers (16); default: Set Single Coil (5) A function code specifies the type of register being addressed by a Modbus request.
MODBUS Write Request: Executed action 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 (various Byte order) | 32bit INT (various Byte order) | 32bit UNIT (various Byte order) | ASCII | Hex | Bool; default: Bool Select data type that will be used for executing action.
MODBUS Write Request: First register number 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).
Trigger output: OutputOpen collector output | Relay output | 4PIN output; default: Open collector output Selects which output will be triggered.
Trigger output: I/O Action Turn On | Turn Off | Invert; default: Turn On Selects the action performed on the output.
MQTT message: JSON format string; default: none Below this field you can find special codes that begin with the '%' sign. Each code represents a piece information related to the status of the device. Include these codes in the field for dynamic information reports.
MQTT message: Hostname host | ip; default: none Broker’s IP address or hostname.
MQTT message: Port integer [0..65535]; default: 1883 Broker's port number.
MQTT message: Keepalive positive integer; default: none The number of seconds after which the broker should send a PING message to the client if no other messages have been exchanged in that time
MQTT message: Topic string; default: none The name of the topic that the broker will subscribe to.
MQTT message: Client ID positive integer; default: none Client ID to send with the data. If empty, a random client ID will be generated
MQTT message: QoS At most once (0) | At least once (1) | Exactly once (2); default: At most once (0) A period of time (in seconds) which has to pass after a trigger event before this Action is executed.

Modbus Serial Master

The Modbus Serial Master page is used to configure the device as a Modbus RTU Master. Modbus RTU (remote terminal unit) is a serial communication protocol mainly used in communication via serial interfaces.


Modbus Serial Device Configuration


This section is used to create Modbus Serial Master's slave device instances. You may create a Serial Device instance for each supported serial interface.

Networking rutos manual modbus modbus serial master device configuration.png

By default there are no instances created. To add a new serial device configuration, enter an instance name and click the 'Add' button.

Networking rutos manual modbus modbus serial master device configuration add button 1.png

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

RS Device Modbus Master Configuration


This section is used to configure the Modbus Serial Master's slave device interface settings.

Networking rutos manual modbus modbus serial master device configuration rs device modbus master configuration v1 1.png

Field Value Description
Enable off | on; default: off Enables this Modbus Serial Device instance configuration.
Name string; default: none Name of the serial device instance. Used for management purposes only.
Device RS232 | RS485 | USB RS232 interface; default: RS232 Specifies which serial port will be used for serial communication.
Baud rate 300 | 1200 | 2400 | 4800 | 9600 | 19200 | 38400 | 57600 | 115200| 230400 | 460800 | 921600 | 1000000 | 3000000; default: 9600 Serial data transmission rate (in bits per second).
Data bits 5 | 6 | 7 |8; default: 8 Number of data bits for each character.
Stop bits 1| 2; default: 1 Stop bits sent at the end of every character allow the receiving signal hardware to detect the end of a character and to resynchronise with the character stream. Electronic devices usually use one stop bit. Two stop bits are required if slow electromechanical devices are used.
Parity Even | Odd| Mark | Space | None; default: None In serial transmission, parity is a method of detecting errors. An extra data bit is sent with each data character, arranged so that the number of 1 bits in each character, including the parity bit, is always odd or always even. If a byte is received with the wrong number of 1s, then it must have been corrupted. However, an even number of errors can pass the parity check.
  • None (N) - no parity method is used.
  • Odd (O) - the parity bit is set so that the number of "logical ones (1s)" has to be odd.
  • Even (E) - the parity bit is set so that the number of "logical ones (1s)" has to be even.
  • Space (s) - the parity bit will always be a binary 0.
  • Mark (M) - the parity bit will always be a binary 1.
Flow control None | RTS/CTS | Xon/Xoff; default: None In many circumstances a transmitter might be able to send data faster than the receiver is able to process it. To cope with this, serial lines often incorporate a "handshaking" method, usually distinguished between hardware and software handshaking.
  • RTS/CTS - hardware handshaking. RTS and CTS are turned OFF and ON from alternate ends to control data flow, for instance when a buffer is almost full.
  • Xon/Xoff - software handshaking. The Xon and Xoff characters are sent by the receiver to the sender to control when the sender will send data, i.e., these characters go in the opposite direction to the data being sent. The circuit starts in the "sending allowed" state. When the receiver's buffers approach capacity, the receiver sends the Xoff character to tell the sender to stop sending data. Later, after the receiver has emptied its buffers, it sends an Xon character to tell the sender to resume transmission.
RS485: Full Duplex off | on; default: off Enables RS485 full duplex.

Modbus Slave Device Configuration


This section is used to create slave instances that the Master (this RUT955 device) will be querying with requests.

Networking rutos manual modbus modbus serial master modbus slave device configuration v1.png

By default there are no instances created. To add a new slave configuration, enter an instance name, select a serial device instance and click the 'Add' button.

Networking rutos manual modbus modbus serial master modbus slave device configuration add button v1.png

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

Slave Device Configuration


The Slave Device Configuration section is used to configure the parameters of Modbus RTU slaves that the Master (this RUT955 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 serial master slave device configuration v1.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 device slave device instance; default: none Specifies which serial device will be used on this slave.
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.
Always reconnect off | on; default: off Create new connection after every Modbus request.
Number of timeouts integer [0..10]; default: 1 Skip pending request and reset connection after number of request failures.
Frequency Period | Schedule; default: Period
Delay integer [0..999]; default: 0 Wait in milliseconds after connection initialization.
Period integer [1..99999]; default: none Interval at which requests are sent to the slave device.
Timeout integer [1..60]; default: 1 Maximum response wait time.
Requests Configuration

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.

Note: Modbus Serial Master uses Register Number instead of Register Address for pointing to a register. For example, to request the Uptime of a device, you must use 2 in the First Register field.

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 v1.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 (various Byte order) | 32bit INT (various Byte order) | 32bit UINT (various Byte order) | ASCII | Hex | Bool; 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.
Remove Brackets off | on; default: off Removes the starting and ending brackets from the request (only for read requests).
off/on slider off | on; default: off Turns the request on or off.
Delete [ X ] - (interactive button) Deletes the request.

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

Modbus Master Alarms

Alarms are a way of setting up automated actions when some Modbus values meet user-defined conditions. When the Modbus Serial Master (this RUT955 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 Modbus Master Alarms list. To create a new Alarm, click the 'Add' button.

Networking rutos manual modbus modbus serial master modbus master alarms add button.png

After this you should be redirected to that Alarm's configuration page which should look similar to this:

Networking rutos manual modbus modbus tcp master alarms configuration v1.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 RUT955 device) perform this request as often as specified in the 'Period' field in Slave Device Configuration.
Compared condition 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 (various Byte order) | 32bit INT (various Byte order) | 32bit UINT (various Byte order) | ASCII | Hex | Bool; default: 16bit INT, high byte first Select data type that will be used for checking conditions.
First register number integer [1..65536]; default: none Number of the Modbus coil/input/holding-register/input-register to read from.
Values various; default: none The value against which the read data will be compared.
Condition More than | Less than | Equal to | Not Equal to | Less or equal | More or equal; default: More than 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.
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 SMS | MODBUS Write Request| Trigger output; default: MODBUS Write Request Action that will be taken if the condition is met. Possible actions:
  • SMS - sends and SMS message to a specified recipient(s).
  • Modbus Request - sends a Modbus Write request to a specified slave.
  • Trigger output - changes state of selected I/O output pin.
SMS: Message string; default: none SMS message text.
SMS: Phone number phone number; default: none Recipient's phone number.
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 Single Coil (5) | Set Single Register (6) | Set Multiple Coils (15) | Set Multiple Registers (16); default: Set Single Coil (5) A function code specifies the type of register being addressed by a Modbus request.
MODBUS Write Request: Executed action 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 (various Byte order) | 32bit INT (various Byte order) | 32bit UNIT (various Byte order) | ASCII | Hex | Bool; default: Bool Select data type that will be used for executing action.
MODBUS Write Request: First register number 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).
Trigger output: OutputOpen collector output | Relay output | 4PIN output; default: Open collector output Selects which output will be triggered.
Trigger output: I/O Action Turn On | Turn Off | Invert; default: Turn On Selects the action performed on the output.


MQTT Gateway

The MQTT Gateway function is used to transfer Modbus data (send requests, receive responses) over MQTT. When it is enabled, the device (this RUT955) 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 v1.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.
QoS At most once (0) | At least once (1) | Exactly once (2); default: Exactly once (2) Specifies quality of service.
Username string; default: none Username for authentication to the MQTT broker.
Password string; default: none Password for authentication to the MQTT broker.
Client ID integer; default: none Specifies client ID for MQTT broker.
Keepalive integer; default: 5 Keepalive message to MQTT broker (seconds)
Use TLS/SSL off | on; default: off Turns TLS support on or off
TLS type cert | psk; default: cert Selects the type of TLS encryption
TLS insecure off | on; default: off Disables TLS security
Certificate files from device off | on; default: off Choose this option if you want to use certificate files generated on device.
CA file string; default: none Upload/select certificate authority file.
Certificates file string; default: none Upload/select certificate file.
Key file string; default: none Upload/select certificate key file.
PSK string; default: none Specifies the pre-shared key.
Identity string; default: none Specifies identity.

Serial Gateway Configuration


Serial Gateway Configuration section displays Serial gateway instances currently existing on the router.

By default the list is empty. To create a new gateway instance, enter the ID of serial device, select serial interface and click the 'Add' button.

Networking rutos manual modbus mqtt gateway serial gateway configuration add button v1 rs232 1.png

After this you should be redirected to instance's configuration page which should look similar to this:

Networking rutos manual modbus mqtt gateway serial gateway configuration rs232 1 v1.png

Field Value Description
Enable off | on; default: off Enables this Serial Gateway instance configuration.
Name string; default: none Name of the gateway instance. Used for management purposes only.
Device RS232 | RS485 | USB RS232 interface; default: RS232 Specifies which serial port will be used for serial communication.
Baud rate 300 | 1200 | 2400 | 4800 | 9600 | 19200 | 38400 | 57600 | 115200| 230400 | 460800 | 921600 | 1000000 | 3000000; default: 9600 Serial data transmission rate (in bits per second).
Data bits 5 | 6 | 7 |8; default: 8 Number of data bits for each character.
Stop bits 1| 2; default: 1 Stop bits sent at the end of every character allow the receiving signal hardware to detect the end of a character and to resynchronise with the character stream. Electronic devices usually use one stop bit. Two stop bits are required if slow electromechanical devices are used.
Parity Even | Odd| Mark | Space | None; default: None In serial transmission, parity is a method of detecting errors. An extra data bit is sent with each data character, arranged so that the number of 1 bits in each character, including the parity bit, is always odd or always even. If a byte is received with the wrong number of 1s, then it must have been corrupted. However, an even number of errors can pass the parity check.
  • None (N) - no parity method is used.
  • Odd (O) - the parity bit is set so that the number of "logical ones (1s)" has to be odd.
  • Even (E) - the parity bit is set so that the number of "logical ones (1s)" has to be even.
  • Space (s) - the parity bit will always be a binary 0.
  • Mark (M) - the parity bit will always be a binary 1.
Flow control None | RTS/CTS | Xon/Xoff; default: None In many circumstances a transmitter might be able to send data faster than the receiver is able to process it. To cope with this, serial lines often incorporate a "handshaking" method, usually distinguished between hardware and software handshaking.
  • RTS/CTS - hardware handshaking. RTS and CTS are turned OFF and ON from alternate ends to control data flow, for instance when a buffer is almost full.
  • Xon/Xoff - software handshaking. The Xon and Xoff characters are sent by the receiver to the sender to control when the sender will send data, i.e., these characters go in the opposite direction to the data being sent. The circuit starts in the "sending allowed" state. When the receiver's buffers approach capacity, the receiver sends the Xoff character to tell the sender to stop sending data. Later, after the receiver has emptied its buffers, it sends an Xon character to tell the sender to resume transmission.
RS485: Full Duplex off | on; default: off Enables RS485 full duplex.

Request messages


Note: MQTT Gateway uses Register Number instead of Register Address for pointing to a register. For example, to request the Uptime of a device, you must use 2 in the Register Number field.

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 (not address) 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 messages


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

Examples


Below are a few examples of controlling/monitoring the internal Modbus TCP Slave on RUT955.


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 RUT955), 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

Modbus TCP over Serial Gateway

The Modbus TCP over Serial gateway serial type allows redirecting TCP data coming to a specified port to an RTU specified by the Slave ID. The Slave ID can be specified by the user or be obtained directly from the Modbus header.

Modbus TCP over Serial Gateway Configuration


Modbus TCP over Serial Gateway Configuration section displays gateway instances currently existing on the router.

By default the list is empty. To create a new gateway instance, enter the name of instance, select serial interface and click the 'Add' button.

Networking rutos manual modbus modbus tcp over serial gateway add button rs232 1 v1.png

After this you should be redirected to instance's configuration page which should look similar to this:

Networking rutos manual modbus modbus tcp over serial gateway configuration rs232 1 v1.png

Field Value Description
Enable off | on; default: off Enables this Modbus TCP over Serial Gateway instance configuration.
Name string; default: none Name of the gateway instance. Used for management purposes only.
Device RS232 | RS485 | USB RS232 interface; default: RS232 Specifies which serial port will be used for serial communication.
Baud rate 300 | 1200 | 2400 | 4800 | 9600 | 19200 | 38400 | 57600 | 115200| 230400 | 460800 | 921600 | 1000000 | 3000000; default: 9600 Serial data transmission rate (in bits per second).
Data bits 5 | 6 | 7 |8; default: 8 Number of data bits for each character.
Stop bits 1| 2; default: 1 Stop bits sent at the end of every character allow the receiving signal hardware to detect the end of a character and to resynchronise with the character stream. Electronic devices usually use one stop bit. Two stop bits are required if slow electromechanical devices are used.
Parity Even | Odd| Mark | Space | None; default: None In serial transmission, parity is a method of detecting errors. An extra data bit is sent with each data character, arranged so that the number of 1 bits in each character, including the parity bit, is always odd or always even. If a byte is received with the wrong number of 1s, then it must have been corrupted. However, an even number of errors can pass the parity check.
  • None (N) - no parity method is used.
  • Odd (O) - the parity bit is set so that the number of "logical ones (1s)" has to be odd.
  • Even (E) - the parity bit is set so that the number of "logical ones (1s)" has to be even.
  • Space (s) - the parity bit will always be a binary 0.
  • Mark (M) - the parity bit will always be a binary 1.
Flow control None| RTS/CTS | Xon/Xoff; default: None In many circumstances a transmitter might be able to send data faster than the receiver is able to process it. To cope with this, serial lines often incorporate a "handshaking" method, usually distinguished between hardware and software handshaking.
  • RTS/CTS - hardware handshaking. RTS and CTS are turned OFF and ON from alternate ends to control data flow, for instance when a buffer is almost full.
  • Xon/Xoff - software handshaking. The Xon and Xoff characters are sent by the receiver to the sender to control when the sender will send data, i.e., these characters go in the opposite direction to the data being sent. The circuit starts in the "sending allowed" state. When the receiver's buffers approach capacity, the receiver sends the Xoff character to tell the sender to stop sending data. Later, after the receiver has emptied its buffers, it sends an Xon character to tell the sender to resume transmission.
Listening IP ip; default: none IP address to listen for incoming connections. (0.0.0.0) value may be used to listen for incoming connections on any interface or IP address.
Port integer [0..65535]; default: none Port number to listen for incoming connections.
Slave ID configuration type User defined | Obtained from TCP; default: User defined Specifies whether slave IDs are user defined or automatically obtained from TCP.
Slave ID integer; default: none Specifies the slave ID of range of permitted slave IDs. The way this field is named and its function depends on the value of the Slave ID configuration field.
A range of IDs can be specified by placing a hyphen (-) between two integer numbers. For example, if you permit slave IDs in the range of 10 to 20, you would specify it as: 10-20
You can also specify multiple values that are not connected in a range using commas (,). For example, to specify 6, 50 and 100 as permitted slave IDs, you would have to use: 6,50,100
Permitted slave IDs range of integers; default: 1-247 Read Slave ID field description.
CRC verification off | on; default: off Checks if sent serial message is not disturbed.
Echo off | on; default: off Turns RS232 echo on or off. RS232 echo is a loopback test usually used to check whether the RS232 cable is working properly.
RS485: Full Duplex off | on; default: off Enables RS485 full duplex.

IP Filter


The IP Filter section is used for configuring which network is allowed to communicate with the device. You may add a new instance by selecting the Interface and pressing Add.

Networking rutos manual console ip filter.png

Then enter the IP address and save.

Networking rutos manual console ip filter instance.png

See also