TRB141 Modbus

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Main Page > TRB Gateways > TRB141 > TRB141 Manual > TRB141 WebUI > TRB141 Services section > TRB141 Modbus

The information in this page is updated in accordance with firmware version TRB1_R_00.07.11.3.


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 TRB141 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 "Advanced" button, located at the top of the WebUI.

Modbus TCP Server

A Modbus TCP Server listens for connections from a TCP Client (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:

Status

This section displays Modbus TCP Server status information.

General settings

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 server 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 client 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 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
Router name 71 72 16 Text
Network registration info 103 104 16 Text
Network type 119 120 16 Text
Current WAN IP address 139 140 2 8 bit unsigned integer
Analog input (PIN 7) value 141 142 2 32 bit unsigned integer
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 month (SIM1) 487 488 4 64 bit unsigned integer (Big Endian Notation)
Mobile data sent last month (SIM1) 491 492 4 64 bit unsigned integer (Big Endian Notation)
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
Mobile data received last 7 days (SIM1) 292 293 2 32 bit unsigned integer
Mobile data sent 7 days (SIM1) 294 295 2 32 bit unsigned integer
Mobile data received last week (SIM1) 503 504 4 64 bit unsigned integer (Big Endian Notation)
Mobile data sent last week (SIM1) 507 508 4 64 bit unsigned integer (Big Endian Notation)
Mobile data received last 30 days (SIM1) 296 297 2 32 bit unsigned integer
Mobile data sent last 30 days (SIM1) 298 299 2 32 bit unsigned integer
PIN 3 status (4 PIN connector) 324 325 1 16 bit unsigned integer
PIN 4 status (4 PIN connector) 325 326 1 16 bit unsigned integer
PIN 3 direction (4 PIN connector) 326 327 1 16 bit unsigned integer
PIN 4 direction (4 PIN connector) 327 328 1 16 bit unsigned integer
Modem ID 328 329 8 Text
Relay 337 338 1 16 bit unsigned integer
Latching relay 338 339 1 16 bit unsigned integer
Isolated input 339 340 1 16 bit unsigned integer
1-wire 340 341 1 16 bit unsigned integer
PIN 1 input status 341 342 1 16 bit unsigned integer
PIN 2 input status 342 343 1 16 bit unsigned integer
PIN 1 (Dry/Wet) status 343 344 1 16 bit unsigned integer
PIN 2 (Dry/Wet) status 344 345 1 16 bit unsigned integer
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 378 379 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
Switch mobile data connection (ON/OFF*) 204 205 1 | 0 Turns mobile data connection ON or OFF
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 3 state 324 325 1|0 Toggles PIN 3 ON or OFF, when output is selected
Switch PIN 4 state 325 326 1|0 Toggles PIN 4 ON or OFF, when output is selected
Switch PIN 3 direction 326 327 1|0 Toggles PIN 3 direction between INPUT (0) or OUTPUT (1)
Switch PIN 4 direction 327 328 1|0 Toggles PIN 4 direction between INPUT (0) or OUTPUT (1)
Switch relay state 337 338 1|0 Turns Relay ON or OFF
Switch latching relay state 338 339 1|0 Turns latching relay ON or OFF
Switch PIN 1 (Dry/Wet) state 343 344 1|0 Switches PIN 1 state to 0 (dry) / 1 (wet)
Switch PIN 2(Dry/Wet) state 344 345 1|0 Switches PIN 2 state to 0 (dry) / 1 (wet)
Switch ACL activity 345 346 1|0 Turns ACL activity 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 Client

A Modbus TCP Client can request data from Modbus servers. The Modbus TCP devices section is used to configure Modbus TCP servers and enable Client.

Notice the Global section config. It is used to outright turn the service off or on if any active configurations are present.

Clicking the Cog icon opens a modal window. The global configuration slider can be set and it's state saved.

By default, the client list is empty and client is disabled. To add a new client, click the 'Add' button

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

Field Value Description
Enabled off | on; default: off Turns communication with the server device on or off.
Name string; default: none Server device's name, used for easier management purposes.
Server ID integer [0..255]; default: none Server ID. Each server in a network is assigned a unique identifier ranging from 1 to 255. When the client requests data from a server, the first byte it sends is the Server ID. When set to 0, the server will respond to requests addressed to any ID.
IP address ip4; default: none Server device's IP address.
Port integer [0..65535]; default: none Server device's Modbus TCP port.
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 servers. The client sends a request to a server specifying the function code to be performed. The server then sends the requested data back to the Modbus client.

Note: Modbus TCP Client 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:

The new Request Configuration should become visible in the list:

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) | 64bit INT (various Byte order) | 64bit UINT (various Byte order) | 64bit float (various Byte order) | ASCII | Hex | Bool | PDU; 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:

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. Note: to use test buttons, you need to enable Client section. A successful response to a test may look something like this:

Alarms Configuration

Alarms are a way of setting up automated actions when some Modbus values meet user-defined conditions. When the Modbus TCP Client (this TRB141 device) requests some information from a server 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 Client 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.

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

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 Client (this TRB141 device) perform this request as often as specified in the 'Period' field in Server 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) | 64bit INT (various Byte order) | 64bit UINT (various Byte order) | 64bit float (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 Ubus event | Email | 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 SMS message to a specified recipient(s).
  • Email - sends Email to a specified recipient(s).
  • Ubus event - sends Email to a specified recipient(s).
  • MQTT message - sends MQTT message to a specified broker.
  • Ubus event - sends ubus event.
  • Modbus Request - sends a Modbus Write request to a specified server.
  • Trigger output - changes state of selected I/O output pin.
SMS: Message string; default: none SMS message text.
SMS: Recipients Single | Group; default: none You can choose to add a single number or use a phone group list.
SMS: Phone group (Group recipient) phone group; default: none Recipient groups, including their associated phone numbers, can be configured here.
SMS: Phone number (Single recipient) phone number; default: none Recipient's phone number.
Email: Subject string; default: none Subject of an email. Allowed characters (a-zA-Z0-9!@#$%&*+-/=?^_`{|}~. ).
Email: Message text string; default: none Message that will be sent if condition passes.
Email: Sender's email account string; default: none Sender's email configuration (configure it here).
Email: Recipient's email address email address; default: none For whom you want to send an email to. Allowed characters (a-zA-Z0-9._%+@-).
MODBUS Write Request: IP address ip | host; default: none Modbus server's IP address.
MODBUS Write Request: Port integer [0..65535]; default: none Modbus server'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 server 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) 64bit INT (various Byte order) | 64bit UINT (various Byte order) | 64bit float (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: OutputConfigurable Input/Output (3) | Configurable Input/Output (4) | Relay (3,4,5) | Latching Relay (11,12,13); default: Configurable Input/Output (3) 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. Possible values: Local time, Unix time, Router name, Device name, Serial number, Current FW version, LAN IP address, Monitoring status, UTC time in ISO, WAN IP address, New line, Modbus server ID, Modbus server IP, First register number, Register value, Mobile IP addresses, Signal strength, Operator name, Network type, Data connection state, Network state, IMSI, IMEI, Modem model, Modem serial number, SIM pin state, SIM state, RSCP, ECIO, RSRP, SINR, RSRQ, ICCID, CELLID, Neighbour cells, Network info, Network serving, WAN MAC address, Analog Current Loop (6,9), Analog Input (6,9), Input (3), Digital Input (1), Output (4), Isolated Output (3,4,8), Isolated Input (2,7), Relay (5,10)
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.
MQTT message: Use root CA off | on; default: off Use root CA for verifying the servers certificates
MQTT message: Use TLS off | on; default: off Turns the use of TLS/SSL for this MQTT connection on or off.
MQTT message: Use credentials off | on; default: off Turns the use of username and password for this MQTT connection on or off.


MQTT Modbus Gateway

The MQTT Modbus Gateway function is used to transfer Modbus data (send requests, receive responses) over MQTT. When it is enabled, the device (this TRB141) 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 server.

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

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

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.

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 one of the following formats:

  • TCP:
 0 <COOKIE> <IP_TYPE> <IP> <PORT> <TIMEOUT> <SERVER_ID> <MODBUS_FUNCTION> <FIRST_REGISTER> <REGISTER_COUNT/VALUES>
  • Serial:
 1 <COOKIE> <SERIAL_DEVICE_ID> <TIMEOUT> <SERVER_ID> <MODBUS_FUNCTION> <FIRST_REGISTER> <REGISTER_COUNT/VALUES>
  • MODBUS TCP connection management messages:
 2 <COOKIE> <CONNECTION_INDEX> <ACTION>

 2 <COOKIE> <CONNECTION_INDEX> 0 <IP_TYPE> <IP> <PORT> <TIMEOUT>

Explanation:

  • Cookie - a 64-bit unsigned integer in range [0..264-1]). 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 server. IPv6 must be presented in full form (e.g., 2001:0db8:0000:0000:0000:8a2e:0370:7334).
  • Port - port number of the Modbus TCP server.
  • Timeout - timeout for Modbus connection, in seconds. Range [1..999].
  • Server ID - Modbus TCP server ID. Range [1..255].
  • Modbus function - Modbus task type that will be executed. Possible values are:
    • 1 - read coils;
    • 2 - read input coils;
    • 3 - read holding registers;
    • 4 - read input registers;
    • 5 - set single coil;
    • 6 - write to a single holding register;
    • 15 - set multiple coils;
    • 16 - write to multiple holding registers.
  • First register - number (not address) of the first register/coil/input (in range [1..65536]) from which the registers/coils/inputs will be read/written to.
  • Register count/value - this value depends on the Modbus function:
    • 1 - coil count (in range [1..2000]); must not exceed the boundary (first coil number + coil count <= 65537);
    • 2 - input count (in range [1..2000]); must not exceed the boundary (first input number + input count <= 65537);
    • 3 - holding register count (in range [0..125]); must not exceed the boundary (first register number + holding register count <= 65537);
    • 4 - input register count (in range [0..125]); must not exceed the boundary (first register number + input register count <= 65537);
    • 5 - coil value (in range [0..1]);
    • 6 - holding register value (in range [0..65535]);
    • 15 - coil count (in range [1..1968]); must not exceed the boundary (first coil number + coil count <= 65537); and coil values separated with commas, without spaces (e.g., 1,2,3,654,21,789); there must be exactly as many values as specified (with coil count); each value must be in the range of [0..1].
    • 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].
  • Serial device ID - a string used to identify a serial device. Must match with Device ID field in MQTT Gateway page Serial gateway configuration section.
  • Connection index - a number used to identify a connection on which an action will be preformed (in range [0..7]).
  • Action - a connection action. Possible values are:
    • 0 - OPEN. This will open a closed connection, reopen an already open connection with the same parameters or close an already open connection and open a new one with new parameters.
    • 1 - CLOSE. This will close an open connection and do nothing to the closed one.
    • 2 - STATUS. This will respond with either OK 1 for an open connection or OK 0 for a closed connection.

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 Server on TRB141.

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 TRB141), 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 also

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