USB-DIO24-CTR6: 24-Channel, USB Digital Input/Output Module with 6 Counter/Timers

ACCES: Committed to Service

We're here to help!

Let our amazing support staff help you with questions: whether finding the right model for you, or technical support on using the product - or figuring out what's wrong - we have the expertise to help you. Use it!

Call, E-Mail, or Chat, Today!


  • 24 channel USB digital I/O module
  • High-Speed USB 2.0 device, USB 3.0 compatible
  • Two 8-bit & two 4-bit ports each software configurable for input or output
  • Field selectable CMOS (+5V) or LVTTL (3.3V) VCCIO signal levels
  • CMOS: All 24 I/O lines buffered with 32 mA sink and source
  • LVTTL: All 24 I/O lines buffered with 24 mA sink and source
  • Two 82C54 counters with all pins available at I/O connector
  • Type B USB connector features industrial strength and high-retention design
  • Jumper selectable I/O pulled up to 5V for contact monitoring, pulled down to ground or floating
  • Jumper selectable power provided via USB cable or external power supply for higher source current capabilities
  • VCCIO at connector for general purpose use, protected by polyfuse
  • Resettable fused +5VDC outputs per 50-pin connector
  • Standard 50-pin IDC header connector with key
  • Alternate micro-fit embedded USB header connector
  • Compatible with industry standard I/O racks like Grayhill, Opto 22, Western Reserve Controls, etc.
  • USB/104 form-factor for OEM embedded applications
  • Small, board itself is PC/104 size (3.550″x3.775″)
  • Custom high-speed function driver (non-HID)
  • Rugged, steel, industrial enclosure measures just 4″x4″x1.25″
  • 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


  • External power for higher source current capabilities
  • Screw terminals for power input provide high retention connection
  • OEM (board only) version for embedded applications
  • Industrial operating temperature (-40°C to +85°C)
  • RoHS Available. Please contact us for ordering information
  • Support for Wind River VxWorks (call for ordering information)
Last updated on November 3, 2023, 9:30 am


In Stock
SKU: N/A Categories: , Tags: , ,


The USB-DIO24-CTR6 is an ideal solution for adding portable, easy-to-install digital I/O and counter capabilities to any computer with a USB port. It is a high-speed USB 2.0 device, offering the highest speed available on the USB 2.0 bus and is fully compatible with both USB 1.1 and USB 3.0 ports. The unit is plug-and-play allowing a quick connection whenever you need additional I/O on the convenience of a USB port.

The board features 24 bits of CMOS/LVTTL-compatible digital I/O with high-current capabilities and two 82C54 counter/timers. Each digital port can be programmed to accept inputs or to drive outputs. Groups of two 8-bit ports and two 4-bit ports are designated as port A, B, CHi and CLo. Power is supplied to the card via the USB cable. For higher current sourcing capabilities, external power may be used. The I/O wiring connections are via an industry standard 50-pin male connector any of our optional terminal block cards. For external circuits, fused +5V (or 3.3V) DC power is available on pin 49 of the connector. The resettable fuse is rated at 0.5A.

All 24 I/O lines are buffered by a type 74LVC8T245 tristate buffer transceiver capable of operating in CMOS (+5V) or LVTTL (+3.3V) modes. The mode is set for all pins simultaneously via an onboard jumper. When using CMOS mode the outputs can sink or source 32 mA. In LVTTL mode the outputs can sink or source 24mA. The 24 bits are divided into four ports: two 8-bit ports (Port A, Port B), and two 4-bit ports (Port CLo, Port CHi). Each port can be configured independently via onboard jumpers for pull-up, pull-down, or no bias. Each port can also be configured independently, via software command, for use as inputs or outputs.

The board is available in two models, one with two 8254 counter/timer chips, and one without. The unit without counters is optimally suited for use with industry standard solid state module mounting racks. Because this version does not place any counter signals on pins normally reserved for Ground, it provides a perfectly compatible 50-pin IDC connection.

The USB-DIO24-CTR6 is designed to be used in rugged industrial environments but is small enough to fit nicely onto any desk or testing station. The board itself is PC/104 sized (3.550 x 3.775 inches, 90mm x 96mm) and ships inside a steel powder-coated enclosure with an anti-skid bottom. A DIN rail mounting provision and extended temperature is available for installation in industrial environments.

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.

Firmware 2.0 Features

Onboard Watchdog Timer. If your application fails to communicate with the device within a specified timeout period (up to hundreds of seconds) the onboard intelligence will change all the output ports and values to the configured “safe” state.

Need a DAC to power up at 1 Volt? Want the digital output port to generate a square wave as soon as the firmware is loaded? Now you can configure the power-on default states for all possible outputs.

Command the onboard intelligence to perform digital input debouncing and latching. Debouncing time constants from hundreds of microseconds to hundreds of milliseconds allows a wide variety of low-pass filtering options. Latching inputs record low- and high-going pulses that your application may otherwise have missed.

PWM allows programmable duty-cycle square wave output on any digital output. MAP is our new Matrix Mapping feature, wherein you can command the onboard intelligence to automagically copy the state of one bit onto another bit, with no computer interaction required.


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. This is especially important since many newer CPU chipsets do not support ISA and have plenty of USB ports. The USB-DIO24-CTR6 OEM board can also be installed using standoffs inside other enclosures or systems. For embedded OEM type applications, an additional miniature USB input header is provided in parallel with the type B connector.

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.


Please contact ACCES with your precise requirement. Examples of special orders would be conformal coating, custom software or product labeling, and more. We will work with you to provide exactly what is required.


  • Home
  • Portable
  • Laptop
  • Education
  • Laboratory
  • Industrial Automation
  • Embedded OEM


Two 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).


The USB-DIO24-CTR6 is available with optional cable assemblies, DIN-rail mountable screw terminal 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. Also available is our low cost IIB-24 which will add optical isolation to any standard 24-channel digital I/O port on a 50 pin connector. To make use of the miniature embedded USB header connector, we offer a variety of micro-fit USB input header cables.

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-DIO24-CTR6 utilizes a high-speed custom function driver optimized for maximum continuous data throughput of 16 MB/s that is hundreds to thousands of times faster than the USB human interface device (HID) driver used by many competing products. This approach maximizes the full functionality of the hardware along with capitalizing on the advantage of high-speed USB 2.0. The boards are supported for use in most USB supported operating systems and includes a free Windows and Linux compatible software package including OSX. This package contains sample programs and source code in C# (.NET), Delphi, and Visual C++, for Windows. Third party support includes a Windows standard DLL interface usable from the most popular application programs and includes example LabVIEW VIs. Embedded OS support includes XP Embedded and Windows Embedded Standard.


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.

USB and Performance

Our USB Data Acquisition products use our “AIOUSB” driver package in Windows and Linux. This driver package includes 32-bit and 64-bit support, and consists of low-level driver components and a high-level API library. This custom interface driver enables our USB devices to achieve 4000 transactions per second, compared to the competitions’ “HID” drivers that cap out around 50 transactions per second. You can read all about the API in the USB Software Reference Manual linked below, and included in every applicable Software Package. (The Linux version of the AIOUSB API is almost identical to the Windows API, and is documented in the aiousb.html file included in the Linux software package.) Like all of our software, full source code is always provided.

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.

TTL Digital Input/Output Lines

  • Channels / Groups: 24 in two 8-bit and two 4-bit groups
  • Type: 8255 Mode 0 compatible
  • Logic Level: VCCIO
  • Pull-up/down: 10kΩ, jumper selectable

VCCIO: Logic Level Selection

Logic Levels 5V 3.3V
Low Inputs ≤ 1.5V ≤ 2uA ≤ 0.8V ≤ 2uA
High Inputs ≥ 3.5V ≤ 2uA ≥ 2.0V ≤ 2uA
Low Outputs ≤ 0.55V 32mA ≤ 0.55V 24mA
High Outputs ≥ 3.8V 32mA ≥ 2.4V 24mA


  • Number / Type: Two 82C54 programmable interval counters
  • Counter Size: 16-bit
  • Logic Level: VCCIO
  • On-Board Clock: 10MHz
  • Clock Pulse Width: High – 30ns (min) Low – 40ns (min)

Bus Type

  • USB 2.0 High-Speed
  • USB 3.0 Compatible
  • USB 1.1 Full-Speed compatible


  • Operating Temperature Range: 0°C to 70°C
  • Storage Temperature Range: -40°C to +85°C
  • Humidity: 5%-90% RH, non-condensing
  • Board Dimension: 3.550 x 3.775 inches
  • Box Dimension: 4.00 x 4.00 x 1.25 inches


  • Basic Unit: 140mA typical (no load)
  • Auxiliary Outputs: +5VDC via 0.5A resettable fuse (500mA trip current)
  • Bus Powered: +5VDC provided via USB bus up to 500mA
  • Externally Powered: Optional on-board external power circuitry and AC/DC (regulated 5V output) adapter can be ordered (“-PR” option) if source current use is expected to be greater than what can be supplied by the USB bus (typically 500mA).

The USB bus is specified to provide 500mA through the USB cable to most desktop environments. This gives you 360mA available on 5VDC (500mA – 140mA = 360mA) for source/sink current output and external power connector (pin 49) for any 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.

Regulatory Compliance

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

ModelDescriptionPrice (USD)

24 DIO USB Module with 6 Counters


24 DIO USB Module

Direct Connect
STB-50D Direct connect 50-pin removable spring-cage terminal board for -U option $49
UTBK-50 Direct connect 50-pin removable screw terminal board $49
Cable Connect
STB-50U Spring-cage terminal board for 50-pin mating connector. $49
STB-50U Kit Spring-cage terminal board (STB-50U) and mounting kit. Includes STB-50U, cable and specialized mounting hardware. $69
STB-50 DIN-rail mountable screw terminal board with latches for 50-pin header $44
CAB50F-6 50-pin ribbon cable with female header connectors, 6 feet long $30
C104-50F-12 50-pin ribbon cable with female headers, 12″ long $15
IIB-24 24-channel optical isolator board for each 50-pin header $149
ROB-24 24-channel electromechanical relay board for each 50-pin header $249
CUSB-LOCK USB Type A to locking Type-B cable $9
Internal USB Cables
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
MP104-DIN DIN-rail mounting provision
USB-104-HUB Rugged, industrial grade, 4-port high-speed USB 2.0 hub
Model Options (call for pricing)
-PR +5VDC external power components and regulated AC/DC adapter
-ST External power connection via screw terminals (high retention)
-OEM Board only model for embedded applications (no enclosure)
-U Replace right angle I/O connector with 50-pin straight up
-T Industrial operating temperature (-40°C to +85°C)
-RoHS RoHS compliant version