USB-FLEXCOM4: Four-port Multiprotocol Serial USB Module

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  • Four-port serial communications adapter
  • Full-speed USB 2.0 device, USB 3.0 and 1.1 compatible
  • Supports field selectable RS-232, RS-422 or RS-485 protocols, per port
  • Includes type FT232BM UART with 384-byte receive/128-byte transmit FIFO buffers
  • Speeds up to 921.6kbps simultaneously
  • Power LED and individual port activity LEDs next to the USB and each COM connector
  • All required power drawn from USB port, no external power adapter required
  • Compact, low profile enclosure
  • Designed, made, supported, and manufactured in the USA


  • OEM (board only) version with PC/104 mounting holes and PCB footprint for added flexibility in embedded applications
  • OEM board with 10-pin vertical male headers instead of DB9s
  • Extended operating temperature (-40°C to +85°C)
  • Wide input (7VDC to 30VDC) power supply input voltage range
  • DIN rail mounting provision
  • RoHS Available. Please contact us for ordering information


  • Multiple POS peripherals
  • Barcode scanners
  • Scales
  • Date-entry terminals
  • Data acquisition and automation modules
Last updated on July 10, 2024, 9:59 am


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This flexible serial communications adapter was designed for effective multipoint transmission in any one of three modes on each channel. These modes are RS232, RS422 and RS485 (EIA485) protocol.


The OEM (board only) version is perfect for a variety of embedded applications. What makes the OEM option unique is that its PCB size and mounting holes match the PC/104 form factor (without the bus connections). This allows our rugged USB to quad-serial port 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. This is especially important since many newer CPU chipsets do not support ISA and have plenty of USB ports. The USB-FLEXCOM4 OEM board can also be installed using standoffs inside other enclosures or systems.


Available accessories include a broad range of cable assemblies and screw terminal boards for quick and easy connectivity. The ADAP9 accessory provides a screw terminal connection to break out the RS-232/422/485 signals on the DB9M connector. Special order items such as conformal coating, custom software, and more, are also available.

Need more isolation?

Isolate your I/O with our USB-ISOLATOR accessory! Tru-Iso™ signal isolation up to 4kV meets EN60601 standards in a rugged industrial-grade, extended temp (-40 to +85°C) package — no connection to power needed! Use with our 1-foot USB cable and avoid tangles. OEM-version available, featuring picoblade microfit headers for hassle-free embedded cabling.


The USB-FLEXCOM4 is plug-and-play which allows quick connect or disconnect whenever you need additional I/O on your USB port. The USB-FLEXCOM4 is supported for use in most USB supported operating systems and includes a free Linux and Windows XP -> 10, both 32 & 64 bit compatible software package. This package contains sample programs and source code in Visual Basic, Delphi, and Visual C++ for Windows. Also incorporated is a graphical setup program in Windows. Embedded OS support includes Windows Xpe, WES7, etc.


Data Sheets



Drivers and Downloads

Full list of available Downloads: Software Packages, Drivers, Manuals, and other documents

Information about our Free Software packages:

ACCES is proud to provide a full suite of software support with every Data Acquisition product. We are committed to supporting the most popular operating systems and platforms for our customers. Currently we are actively supporting XP -> 10, both 32 & 64 bit, including “Server 2008,” “Embedded,” and “Compact” flavors for all plug-and-play products including PCI, PCI Express, USB, and more. Many products continue to ship with support for additional operating systems such as DOS, Windows 95, 98, Me, NT4, and 2000.


Among the software we deliver with our products are sample programs in a wide variety of programming languages. These samples are used to demonstrate the software interfaces to our products — and many can be used as-is in your production environments, or to test functionality of the devices out-of-the-box. We’re currently actively supporting sample programs in Microsoft Visual C#, Visual Basic, Delphi, and Visual C/C++, with many devices including samples in Borland C/C++ 3.1 for DOS. Additionally we provide National Instruments LabVIEW compatible DLLs and many demonstration VIs for our devices.


Drivers for various operating systems are also provided, including active support for Windows XP -> 10 — all in both 32-bit and 64-bit flavors, and including consumer, server, and embedded varieties — as well as the 2.6 and newer Linux kernels and recent OSX / macOS versions. Many products continue to ship with driver support for Windows 95, 98, Me, NT4, and Windows 2000, but support for these operating systems is considered deprecated.

Setup Programs and Utilites

Our Data Acquisition devices also include a graphical setup utility that walks you through the process of configuring any option jumpers or switches on the device, as well as explaining a little about the various connectors present.

Many devices also include utility programs – little tools to make your use of the device easier, such as EWriter, a program that allows you to read and write data in the user-accessible EEPROM locations on all our USB data acquisitition products; or WinRISC, a “Really Incredibly Simple Communications” terminal program that lets you get started instantly with serial devices.

“Register Level” Documentation

Besides all this software in all these languages and operating systems ACCES has a policy of open and transparent development: none of our lowest-level “register” interfaces are hidden from you — we document every register in every bus card, every command in every serial board, and every usb control transfer in every USB Data Acquisition board. These lowest-level interfaces allow you to develop for our products in ANY operating system or language, regardless of our actively supporting it or having a driver for it. We have customers actively developing in ADA, Android, Python, Java, MATLAB, Solaris, and more, just by referring to our complete low-level interface documentation! And we provide the full source code to all of our drivers, regardless of operating system, to give you an even bigger head start in your own development tasks.

No Fees or Royalties

All of this software is provided at no additional charge, and is licensed under any of a variety of flexible — and royalty free — options. Check out our software license explanation if you’d like more information.

Custom Software

ACCES also offers Custom Software Services for our products. Our prices are unbelievably low, often as inexpensive as free! If you need something tweaked to support your needs, or an entire enterprise application developed from scratch, it is definitely worth your time to inquire with us, first.

Further information about available ACCES Software:

Redistributing Windows Drivers
A list of ACCES drivers and the files that compose them under different versions of Windows, so you can easily redistribute ACCES cards and drivers.

Communications Interface

  • Serial Ports: COM A through COM D via four male DB9 connectors
  • Character length: 5, 6, 7, or 8 bits
  • Parity: Even, odd or none
  • Stop Interval: 1, 1.5, or 2 bits
  • Serial Data Rates: Up to 921.6k for RS-422 and RS-485 modes, asynchronous RS-232 speeds up to 230.4kbps.
  • Receiver Input Sensitivity: +200 mV, differential input
  • Common Mode Rejection: +12V to -7V
  • Transmitter Output Drive: Up to 60 mA, with thermal shutdown
  • Bus Type USB 2.0 Full-Speed
  • USB Connector: Type B, high-retention
  • Embedded USB Connector 5-pin header, Molex part number 53047 Mating connector housing is Molex part number 51021 0500 -OEM VERSION


  • Operating Temperature: 0°C to +60°C (Optional 40°C to +85°C)
  • Storage temperature: -50°C to +120°C
  • Humidity: 5% to 95%, non-condensing
  • Power Required: 5VDC at approximately 110 mA (plus loads up to an additional 240 mA) from USB bus
  • Size: Board Dimension: 3.550 x 3.775 inches (PC/104 size & mounting)
  • Box Dimension: 4.00 x 4.00 x 1.25 inches
    Pinout Table
    DB-9 Male Pin for each of Ch A-D RS-232 Signals (Industry Standard) RS-485 Signals (2 Wire) RS-422 Signals (Also 4wire RS485)
    Ch x pin 1 DCD RX-
    Ch x pin 2 RX TX+/RX+ TX+
    Ch x pin 3 TX TX-/RX- TX-
    Ch x pin 4 DTR
    Ch x pin 5 Gnd Gnd Gnd
    Ch x pin 6 DSR
    Ch x pin 7 RTS
    Ch x pin 8 CTS
    Ch x pin 9 RI RX+
ModelDescriptionPrice (USD)

USB Four Port RS-232 Module


USB Four Port RS-232/422/485 Module

ADAP9 Screw terminal adapter (single DB9 female to 9 screw terminals) $19
ADAP9-2 Screw terminal adapter (dual DB9 female to 18 screw terminals) $25
STB-10 Screw Terminal Board, 10 pin male header $44
MP104-DIN DIN-rail mounting provision
CUSB-EMB-1 1ft USB Type A to micro-fit OEM header $19
CUSB-EMB-6 6ft USB Type A to micro-fit OEM header $19
CUSB-EMB-HDR 30″ USB 1×5 standard header to micro OEM cable $19
CUSB-EMB-HDRM 30″ USB 1×5 metric header to micro OEM cable $19
CUSB-EMB 6″ micro-fit to micro-fit embedded OEM cable $19
USB-104-HUB Rugged, industrial grade, 4-port high-speed USB 2.0 hub
Options (call for pricing)
-OEM Board-only version for embedding in systems
-F Fast version (RS-232 up to 921.6kbps)
-HDR OEM board with 10-pin vertical male headers instead of DB9s
-P External power components and AC/DC adapter
-T Extended operating temperature (-40°C to +85°C)
-Call Custom baud rates
-RoHS RoHS compliant version
-WI Wide input (7VDC to 30VDC) power supply input voltage range