USB to RS-232C isolation voltage is 3kVdc.
[ Composition ]

Converter: 1
USB cable: 1
Utility CD: 1
Instruction Manual: 1 ( in Japanese only)

Warranty: 1

SI-55USB is an USB converter, which converts USB of PC into RS-232C serial port of signal-isolated type. Virtual COM port driver ease the usage of test software and shorten the time of installing the new system. Features of this product are max 1Mbps baud rate and 3000V high-voltage resistant isolation by photo coupler and isolated power unit.

Supporting wide range of temperature, metal enclosure, and noise resistant make it possible to use in the factories, inspection lab and so on.

<Image of using SI-55USB>



  1. RS-232C connector (DSUB9pin male)
  2. USB connector
  3. Power LED
  4. Data status LED
Pin Assignment
Terminal # Name I/O*1 Explanation
1 DCD In Data Carrier Detect
2 RXD In Received Data
3 TXD Out Transmitted Data
4 DTR Out Data Terminal Ready
5 GND - Signal Ground
6 DSR In Data Set Ready
7 RTS Out Request To Send
8 CTS In Clear To Send
9 RI In Ring Indicator
*1: “Out”: Output signal from converter. “In”: Input signal toward converter. “I/O”: Both ways.
< Mounting on the DIN rail >
Screw on the bottom using the M3 screw.


Conversion USB⇔RS-232C
USB Interface USB1.1/2.0 full speed transmission connector B
LED Transmission: TXD, Reception: RXD, Power: PWR
Serial Interface RS-232C DSUB9pin male (inch screw)
Serial Signal TXD, RXD, RTS, CTS, DSR, DTR, DCD, RI
Asynch type Asynch
Baud Rate 300bps to 1Mbps*1
Data Frame Data bits [7or8] + Parity [Even/Odd/none] + Stop bits [1/2]
Flow Control Xon/off, RTS/CTS (supported by COM port emulator)
Mounting Method Using M3 screw hole in the bottom, installation to a DIN rail (SI-DIN70 is required.)
Signal Isolation Protection 3000Vdc
System requirements
(USB equipment)
PC: PC/AT compatible with USB ports (DOS/V PC)
OS: Windows® 7/8/8.1/10*2
Power USB Bus power,  DC5V±10%, Max. 270mA
Power Consumption 1.4W or less
Temperature In operation: -10 to 55°C, In storage: -20 to 75°C
Humidity In operation: 10 to 90%RH,
In storage: 10 to 90%RH (no condensation)
Dimension 65(W) x 95(D) x 22(H) mm
Weight Approx. 200g
Composition USB cable (1.8m), Utility CD, Instruction manual (in Japanese only), Warranty.
*1: Speed is established in application software
*2: Supports 32bit/64bit of Windows 7/8/8.1/10