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Thomas Supplier



Two-Port USB to Serial RS-232/422/485 Adapter

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  US Prices
CDN Prices

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FEATURES Specifications
  • Serial adapter for USB 1.1 and 2.0 port hosts
  • Two serial ports—field selectable RS-232/422/485
  • Small, (4" x 4" x 1.8") rugged industrial enclosure
  • PC/104 module size and mounting compatibility
  • Speeds up to 921.6Kbps
  • Power and individual port activity LEDs
  • All required power drawn from USB port, no external power adapter required
  • Extra downstream USB expansion port



  • OEM (board only) version with PC/104 mounting holes and PCB footprint for added flexibility in embedded applications
  • DIN rail mounting provision for industrial environments
  • RoHS Available. Please contact us for ordering information


The USB-COM-2SM is a two-port asynchronous serial communication adapter designed for use with any computer system equipped with a USB port. Multiple peripherals such as POS, barcode scanners, scales, date-entry terminals, data acquisition modules, and automation equipment can now be recognized and used on a single USB port. Simply install the included software and connect the unit to your USB port. It instantly provides two RS-232, RS-422, or RS-485 serial ports which can be selected on a port by port basis. It is now easier than ever to add serial ports and serial devices to any application along with easy plug-and-play and hot-swapping features.

The unit enclosure is 4 inches wide by 4 inches deep by 1.8 inches high. The adapter is supplied with a 6 foot USB cable and has two male DB9 connectors with jack-screws for secure cable connections. The DB9 connectors are conveniently located at the front of the unit and feature easy-to-read LEDs indicating serial port activity. The USB connector is located at the back of the unit and also features a LED for USB status.

The USB-COM-2SM is fully compatible with both USB 1.1 and USB 2.0 ports. The OEM (board only) version provides just the board without the enclosure and is ideal for a variety of embedded OEM applications. An additional USB input header is provided on the board for OEMs along with a downstream USB port for connecting additional USB devices.



Type FT232 UARTs are used as asynchronous communication elements. This includes 384-byte receive / 128-byte transmit FIFO buffers for high data throughput and to protect against lost data in multitasking systems. Crystal oscillators located on the card permit precise baud rate capability up to 230.4K for use in RS-232 mode, using ICL3243 type drivers. Speeds up to 921.6K are achievable using RS-422 & RS-485. The driver/receivers used are type SP491 which are capable of driving long communication lines at high baud rates. They can drive up to ±60 mA on balanced lines and receive inputs as low as 200 mV differential signal superimposed on common mode noise of 12V to -7V. In case of communication conflict, the driver/receivers feature thermal shutdown.


What makes the OEM (board only) option unique is that its PCB size and mounting holes match the PC/104 form factor (without the bus connections). This allows our rugged serial board to be added to any PCI-104 or PC/104 stack by connecting it to a simple USB port usually included on-board with embedded CPU form factors such as EBX, EPIC, and PC/104 — especially important since many newer CPU chipsets do not support ISA and have plenty of USB ports. The USB-COM-2SM OEM board can also be added into many pre-existing standard PC/104 based systems and enclosures. The OEM version is perfect for a variety of embedded applications. The board's pre-drilled mounting holes allow for installation using standoffs inside most enclosures or systems.

High Retention USB Connector

The ever-growing presence of USB in the industrial/military marketplace has driven the need for USB connections to be reliable, dependable, and unfailing. Gone are the days of loose USB connections. A type B USB connector is used on all ACCES USB/104 products which features a high retention design that complies with the class 1, Div II minimum withdrawal requirement of over 3 pounds of force (15 Newtons). This connector has an orange color-coded insulator to quickly differentiate it from standard USB connectors. Using these USB connectors increases reliability in your system and ensures a tight connection. For embedded OEM type applications, an additional miniature USB input header is provided in parallel with the type B connector.


This board has two miniature OTG USB onboard five pin connectors. One connector allows you the added feature of connecting to a spare USB port on the onboard USB1.1 hub. This would provide an additional, 'daisy-chained' USB 1.1 bus to which you can attach an additional ACCES I/O USB product or any 3rd party USB devices you may wish. Up to 180mA is still available without requiring the added device to have its own 5VDC power source. The second five pin connector allows the board to have an onboard USB connection rather than the standard type B connector that is accessible externally on the enclosure. This is useful in OEM embedded or high vibration applications where a tighter fit USB connection is required than a standard USB plug.



The industrial communications market commonly uses RS-422 and RS-485 interfaces due to their differential lines providing robustness, longer cabling and ability to withstand industrial noise. The USB-COM-2SM with its tiny enclosure and its easy connectivity provides portable connections to laptops for this kind of industrial monitoring for the mobile test market. At the same time, conventional RS-232 devices can also be supported. The USB-COM-2SM unit can be used in the following markets.


  • Home
  • Portable and laptop
  • Education
  • Industrial Automation and Control
  • Embedded OEM
  • Point of Sale (POS) Retail
  • Serial Data Acquisition
  • Serial Instrumentation
  • Laboratory Research
  • Remote Access



The USB-IIRO4-2SM is available with optional cable assemblies, screw termination boards and DIN rail mounting provisions.



The USB-COM-2SM features hot-plug functionality which allows quick connect or disconnect whenever you need additional serial communications on your USB port. A Complete Software Support Package is provided including an easy to use terminal program for testing out your COM ports. This package contains sample programs and source code in Visual Basic, Delphi, C Builder, and Visual C for Windows. Also incorporated is a graphical setup program in Windows. The adapter installs as Standard COM ports in all Windows and Linux operating systems. Supported operating systems include Windows, Linux, WinCE.net, Mac OS-8, OS-9, OS-X. Use in other operating systems may also be supported, contact Factory.



Connector Pin Assignments

USB-COM-2SM has two 9-pin connectors for the serial ports. Connector pin assignments are listed below.


Serial Connector Pin Assignments
DB-9 Male Pin for
each of Ch A-B
RS-232 Signals
(Industry Standard)
RS-485 Signals
(2 Wire)
RS-422 Signals
(Also 4wire RS485)
Ch x - 1 DCD RX-/TX- RX-
Ch x - 2 RX TX /RX TX
Ch x - 3 TX TX-/RX- TX-
Ch x - 4 DTR    
Ch x - 5 Gnd Gnd Gnd
Ch x - 6 DSR    
Ch x - 7 RTS    
Ch x - 8 CTS    
Ch x - 9 RI RX /TX RX




Communications Interface

  • I/O Connections: There are 9 pins per port including common grounds. All RS-232 signals are supported and present at the DB9 connectors.
    • RS-422 data signals – Tx , Tx-, Rx , Rx-, GND
    • RS-485 data signals –
      • 2 wire: Tx/Rx , Tx/Rx-, GND
      • 4 wire: Tx , Tx-, Rx , Rx-, GND
      • Jumper selectable termination
  • Serial Data Rates:
    • Up to 230.4K bps, asynchronous for RS-232
    • Up to 921.6K bps, asynchronous for RS-422 and RS-485
  • Multidrop: Compatible with RS-485 specifications. Up to 32 drivers and receivers allowed on line. Driver / Receivers used are type SP491.
  • Character Length, Parity and Stop Interval: 5,6,7, or 8 bits; Even, odd, or none; 1, 1.5, or 2 bits
  • Receiver Sensitivity: ±200 mV differential input
  • Common Mode Voltage: 12V to -7V
  • Transmitter Output Drive: 60 mA with thermal shutdown
  • Termination: Jumper selectable per channel for RS-485 mode
  • Bias: On-board from factory on transmit lines for RS-485 & RS-422


Bus Type

USB 1.1 and 2.0 host compatible

Power Required

5V@ 120mA maximum
0-60mA for each COM channel
5VDC provided via USB cable up to 500mA



  • Operating Temperature Range: 0°C. to 60°C.
  • Storage temperature Range: -50°C. to 120°C.
  • Humidity: 5% to 95%, non-condensing.
  • Size: 4 inches wide by 4 inches deep by 1.8 inches high


Regulatory Compliance

  • This product is in full compliance with CE requirements.

When ordering RoHS products, please identify this need by using a unique model number suffix, "-RoHS" on all orders. For pricing and lead times, please contact your sales representative.
Part Number Price(USD)
USB-COM-2SM-OEM please call


USB-COM-2SM Two port USB to RS-232/422/485 serial adapter
-OEM board only version (no enclosure)

 View / Download USB-COM-2SM Data Sheet (in .pdf format)

 View / Download USB-COM-2SM Manual (in .pdf format)

Acquisition Control Communications Engineering / Systems
USA Office

Address: 1480 Gulf Road, Suite 837,
PO Box 1364
Point Roberts, WA 98281

Western Canada - Vancouver BC

Tel:1.800.663.6001 or 1.604.925.6150
Address: 2454 Haywood Ave
West Vancouver, BC V7V 1Y1

Eastern Canada - Markham, Ontario

Tel:1.800.465.0164 or 1.905.513.7027