USB-DIO-32I: USB 32-Bit Independently Selectable Digital I/O Module

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  • Small (3.5 by 3.7 in.), portable, 32-channel USB digital I/O module
  • 32-bits independently selectable for inputs or outputs
  • High-speed USB 2.0 device, USB 3.0 and 1.1 compatible
  • All 32 I/O lines buffered with Sink 64mA / Source 32mA current capabilities
  • Standard 50-pin IDC connector with key
  • Removable screw terminal adaptor for easy wiring
  • USB/104 form-factor for OEM embedded applications
  • OEM version (board only) features PC/104 module size and mounting compatibility
  • Alternate micro-fit embedded USB header connector
  • Custom high-speed function driver (non-HID)
  • Type B USB connector features industrial strength and high-retention design
  • Small (4″ x 4″ x1.25″) rugged industrial enclosure
  • Labview VI driver
  • Now with Firmware 2.0 features!
    Onboard Watchdog Timer, configurable power-on defaults, digital input debouncing and latching, digital output Pulse Width Modulation (PWM) and Matrix Mapping
  • Support for Wind River VxWorks (call for ordering information)
  • Designed, made, supported, and manufactured in the USA


  • Extended operating temperature (-40° to +85°C)
  • External power components and AC/DC adapter
  • Screw terminals for power input provide high retention connection
  • OEM (board only) version with PC/104 mounting holes and PCB footprint for added flexibility in embedded applications
  • 24-channel version compatible with industry standard I/O racks like Grayhill, Opto 22, Western Reserve Controls
  • RoHS Available. Please contact us for ordering information
Last updated on January 25, 2024, 10:16 am


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The USB-DIO-32-OEM is an ideal solution for adding embedded, portable, easy-to-install digital I/O and counter capabilities to any computer with a USB port. The USB-DIO-32-OEM is a USB 2.0 device, offering the highest speed available with the USB bus. It is fully compatible with both USB 1.1 and USB 2.0 ports. The board is plug-and-play allowing quick connect or disconnect whenever you need additional I/O on your USB port.

The USB-DIO-32-OEM features 32 bits of TTL-compatible digital I/O with high-current capabilities and three optional 82C54 counters. Each digital port can be programmed to accept inputs or to drive outputs on four 8-bit ports, designated as port A, B, C, and D. Power is supplied to the unit via the USB cable or for higher current capabilities, external power may be used. The I/O wiring connections for USB-DIO-32 are via an industry standard 50-pin connector. For external circuits, fused +5VDC power is available at the connector. This resettable fuse is rated at 0.5A.

The USB-DIO-32-OEM is designed to be used in rugged industrial environments, with extended temperature available. The board is PC/104 sized (3.550 x 3.775 inches, 90mm x 96mm) for added flexibility in embedded applications and is small enough to fit nicely onto any desk or testing station.

All I/O lines are buffered by a type 74ABT245 tristate buffer transceiver capable of sinking 64 mA or sourcing 32 mA. The buffers are configured under program control for input or output. Pull-ups (to +5 VDC) or pull-downs (to ground) on the board allow for contact monitoring and assure that there are no erroneous outputs at power-up until the module is initialized by system software.

Unlike most USB digital I/O products which primarily use a human interface device (HID) driver, ACCES offers an easy to use, Windows-based, custom function driver optimized for maximum data throughput. This approach exposes the full functionality of the hardware along with maximizing the advantage of using the high-speed USB 2.0 bus.


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 pre-drilled mounting holes match the PC/104 form factor (without the bus connections). This ensures easy installation using standard standoffs inside most enclosures or systems. The board can be added to any PC/104, PCI-104, or PCI/104-Express stack by connecting it to a USB 2.0 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. Future stacks will be using the extremely fast PCI Express bus which is essentially overkill for simple monitoring and control. For embedded OEM type applications, an additional micro-fit USB input header is provided.

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 micro-fit USB input header is provided in parallel with the type B connector.

Optional Enclosure

The USB-DIO-32-OEM is available packaged in a rugged, steel enclosure with an attractive black powder coat finish and an anti-skid bottom. The enclosure is useful in industrial environments and protects the board from potential environmental hazards. The unit enclosure is 4 inches wide by 4 inches deep by 1.25 inches high and features a DIN rail mounting provision. Please visit the USB-DIO-32 webpage to order the enclosed unit.


  • Mobile Solutions
  • Test Equipment
  • Kiosks
  • Robotics
  • Machine Control
  • Laboratory Monitoring and Control
  • Security Systems, Energy Management
  • Relay Monitoring and Control
  • Sensing Switch Closures or TTL, DTL, CMOS Logic
  • Driving Indicators or Recorders
  • Industrial Automation
  • Embedded OEM


Three 82C54 chips each include three 16-bit counter/timers factory configured in an optimal module for use as event counters, frequency output, pulse width, and frequency measurement (see the Block Diagram).

Optional Accessories

The USB-DIO-32-OEM is available with optional cable assemblies, screw termination boards, and an external AC/DC power supply. The pin connections are also compatible with industry standard I/O racks such as ACCES A24A, Grayhill, Opto 22, Western Reserve Controls, etc. with optional cable. A DIN rail mounting provision is also offered.


  • Three 82C54 counter/timers
  • Extended operating temperature (-40°C to +85°C)
  • External power components and AC/DC adapter
  • Screw terminals for power input provide high retention connection
  • 24-channel version compatible with industry standard I/O racks like Grayhill, Opto 22, Western Reserve Controls
  • RoHS Available. Please contact us for ordering information
  • Support for Wind River VxWorks (call for ordering information)


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.


ACCES has successfully partnered with Wind River to bring our entire line of USB DAQ boards to VxWorks 7!

Our newly available driver and easy-to-use API-library, including full source and sample code, supports ReNumeration for loading firmware across the USB cable as well as our GenericVendorWrite and GenericVendorRead functions, compatible with our Windows AIOUSB.dll API. Additional AIOUSB API functions are being ported, ask for details!

With our aioUSB.VxWorks library USB DAQ can now be used with the utmost confidence for real-world/real-time/rugged applications. Using VxWorks 7 as the solid foundation, and positive-retention cables in either micro-fit or USB-B-with-screw, as well as rugged steel enclosures and DIN-Rail or PC/104-mounting options, USB is no longer “just for desktops”.

You can find more information about our VxWorks libraries and services on our Wind River Silver Partner page.

Digital Inputs (TTL Compatible)

  • Logic High: 2.0 to 5.0 VDC
  • Logic Low: -0.5 to +0.8 VDC

Digital Outputs

  • Logic High: 2.0 VDC min., source 32 mA
  • Logic Low: 0.55 VDC max., sink 64 mA

Optional Counter/Timers

  • Type: 82C54-10 programmable interval counters
  • Output Drive:
    • 2.0 VDC min., source 32 mA
    • 0.55 VDC max,. sink 64 mA
  • Input Gate: TTL/CMOS compatible
  • Clock: On-board, 3 MHz crystal-controlled clock
  • Active Count Edge: Negative Edge
  • Minimum Clock Pulse Width: 30 nS high, 40 nS low
  • Timer Range: 16 bits
  • Maximum Input Frequency: 10MHz


  • Operating Temperature Range: 0° to 70°C (optional -40°C to +85°C)
  • Storage Temperature Range: -40° to +85°C
  • Humidity: Maximum 90% RH, without condensation
  • Board Dimension: 3.550 x 3.775 inches


  • +5VDC @ ~ 80mA typical including three counters (no load)
  • +5VDC derived from the USB bus cable o external power supply depending on the user configuration
  • +5VDC resettable fuse at 0.5A located on ouput on 50-pin connectors (pin 49) for external application use

The USB bus is specified to provide 500mA through the USB cable to most desktop environments. This gives you 420mA available on 5VDC (500mA – 80mA = 420mA) for source/sink current output and external power connector (pin 49) use for a particular application. If using more than a total of 500mA, or your USB port/hub has less then the 500mA normally provided, use optional 5VDC external power supply (-PR option) and remove VUSB jumper and place jumper on VEXT. Then plug in external power before plugging into USB port.

Connector Pin Assignments

USB-DIO-32-OEM has a 50-pin connector provided for I/O connections. Connector pin assignments are listed below.

Assignment Pin Assignment Pin
Port C PC7 1 Counter A0 Freq In 2
Port C PC6 3 Ctr A1 P.W.I. (Gate) 4
Port C PC5 5 Counter A2 Freq Out 6
Port C PC4 7 Counter B0 Freq In 8
Port C PC3 9 Ctr B1 P.W.I. (Gate) 10
Port C PC2 11 Counter B2 Freq Out 12
Port C PC1 13 Counter C0 Freq In 14
Port C PC0 15 Ctr C1 P.W.I. (Gate) 16
Port B PB7 17 Ctr C2 Freq Out 18
Port B PB6 19 Port D PD7 20
Port B PB5 21 Port D PD6 22
Port B PB4 23 Ground 24
Port B PB3 25 Port D PD5 26
Port B PB2 27 Ground 28
Port B PB1 29 Port D PD4 30
Port B PB0 31 Ground 32
Port A PA7 33 Port D PD3 34
Port A PA6 35 Ground 36
Port A PA5 37 Port D PD2 38
Port A PA4 39 Ground 40
Port A PA3 41 Port D PD1 42
Port A PA2 43 Ground 44
Port A PA1 45 Port D PD0 46
Port A PA0 47 Ground 48
Fused +5 VDC . 49 Ground 50

Regulatory Compliance

This product is designed to be in full compliance with CE requirements.

ModelDescriptionPrice (USD)

USB, 32 Individually selectable for Input or Output

Direct Connect
UTBK-50 Direct connect 50-pin removable screw terminal board $49 (included with standard product).
STB-50U KIT Spring-cage terminal board (STB-50U) and mounting kit. Includes STB-50U, cable and specialized mounting hardware. $69
Cable Connect
STB-50U Spring-cage terminal board for 50-pin mating connector.
STB-50 DIN-rail mountable screw terminal board with latches for 50-pin header
CAB50F-6 50-pin ribbon cable with female header connectors, 6 feet long
C104-50F-12 50-pin ribbon cable with female headers, 12″ long
MP104-DIN DIN-rail mounting provision
Signal Conditioning
IIB-24 24-channel optical isolator board for each 50-pin header
ROB-24 24-channel electromechanical relay board for each 50-pin header $249
USB Connectivity
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)
-E Economy module, no screw terminal board
-OEM Board only model, no enclosure or screw terminal board
-PR +5VDC external power components and regulated AC/DC adapter
-ST External power components & screw terminals for power input (high retention)
-T Extended operating temperature (-40°C to +85°C)
-RoHS RoHS compliant version
-Call 24-channel version compatible with industry standard solid state module racks