SWM282 Modbus

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The information in this page is updated in accordance with firmware version SWM2_R_00.01.06.3.

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 SWM282 devices.

Note: Modbus TCP Server is additional software that can be installed from the System → Package Manager page.

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 Server window section and the table below provides information on the fields contained in that window:

Status

Status section displays Modbus TCP Server status information:

Modbus TCP server

In this section you can configure the main server settings:

Field	Value	Description
Enable	off \| on; default: off	Enable Modbus TCP server.
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.
Enable broadcasts	off \| on; default: off	Process incoming Modbus broadcast messages.
Keep persistent connection	off \| on; default: on	Do not close the connection after each completed Modbus request.
Connection timeout	integer [0..60]; default: 0	Timeout in seconds: this parameter specifies the duration after which the connection will be forcefully closed. A value of 0 is considered the same as no timeout.
Enable custom register block	off \| on; default: off	Allows the usage of custom register block.
Register file path	path; default: /mnt/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 [10000..65536]; default: 10000	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).

To get port-specific registers, use following formula: register_number + (port_number * register_count).

For example, to get register number:

TX of port1: 1001 + (0 * 4) = 1001.
TX of port2: 1001 + (1 * 4) = 1005.

The register numbers and corresponding system values are described in the table below:

required value	register address	register number	number of registers	representation
Uptime	1	2	2	32 bit unsigned integer
Hostname	3	4	16	ASCII
Serial number	19	20	16	ASCII
WAN IP	35	36	2	8 bit unsigned integer
LAN MAC	37	38	16	ASCII
Device name	53	54	16	ASCII
Unix timestamp	69	70	2	32 bit unsigned integer
Local ISO time	71	72	12	ASCII
UTC time	83	84	12	ASCII
Port TX counter	1000	1001	4	64 bit unsigned integer
Port RX counter	2000	2001	4	64 bit unsigned integer
Port link status (up/down)	3000	3001	1	16 bit unsigned integer

Set Parameters

The Modbus daemon can also set some device parameters.

value to set	register address	register number	register value	description
Hostname	3	4	Hostname (in decimal form)	Changes hostname
Device name	53	54	Device name (in decimal form)	Changes device name
Reboot	97	98	1	Reboots the switch