ModbusTCP ⇔ ModbusRTU/ASCII
(LAN ⇔ RS-422/485)
Interface Converter


●Connects 10Base-T/100Base-TX by auto-detection.
●Supports Modbus TCP master mode and Modbus TCP slave mode
●When master mode, you can register up to 8 IP addresses of Modbus TCP slave for the range of Modbus ID with which it connects.
●When slave mode, it connects up to 10 Modebus TCP master devices simultaneously to share the control of the access.
●Automatic register-scanning function of the slave mode makes the response for request by the master more quick.
●Can be used in the temperature between -25 and 75 degree Celsius.
●Low power consumption. It supports DC5 to 30V wide input.
●Supports installation by the wall bracket, the magnet, and installation to 35mm DIN rail.

SI-485MB is a Modbus gateway to convert bi-directionally Modbus RTU/ASCII of serial interface to Modebus TCP of Ethernet. The firmware for gateway process supports Modbus TCP master mode and Modbu TCP slave mode and supports all the current ModbusRTU/ASCII register and command conversion. The robust metal body, broad range of temperature, wide input voltage range, and the support for installation by options such as 35mm DIN rail and wall bracket allow you to use it for factory automation without worry.

  1. AC adapter jack
  2. RS-422/485 terminal
  3. LAN connector
  4. Power LED
  5. Data status LED
  6. Driver status LED
  7. Dip switch

LAN connector LED
Left Right Meaning
Off   Not connected
Light in Orange   10BASE-T linked
Light in Green   100BASE-TX linked
  Off No Communication
  Blink in Orange Communicating in half duplex
  Blink in Green Communicating in full duplex


RS-422/485 terminal
Number Name Full duplex*1 Half duplex*1
I/O direction*2 Description I/O direction*2 Description
1 SD+ Out Send data+ - Cannot used*3
2 SD- Out Send data- - Cannot used*3
3 RD+ In Receive data+ I/O Send/Receive data+
4 RD- In Receive data- I/O Send/Receive data-
5 GND - Signal ground - Signal ground
6 DC-IN 5 to 30V - External power input   External power input
*1: Can be switched by the dip switch or setting.
*2: "Out" means when signal outputted from the converter and "In" means when signal is inputted. Both direction is "I/O".

[ Connector side ]


[ Modbus master mode ]

You can use Modbus RTU/ASCII master device as Modbus TCP master by using SI—485MB in master mode. Once the SI-485MB receives a Modbus RTU-ASCII frame (query message) from the master device of the RS-422/485, it connects to the IP address indicated in the address field of the frame or to the specified IP address and then it transmits the data in Modbus TCP frame format.

[ Modbus slave mode ]

You can use Modbus RTU/ASCII slave devices as Modbus TCP slaves by using SI-485MB in slave mode. Once the SI-485MB receives a Modbus TCP frame (query message) from the Modbus TCP master device, it transmits the data to the RS-422/485 side in Modbus RTU/ASCII frame format. SI-485MB allows up to 10 Modbus TCP master devices, and control the shared access.