IOD-24: ISA 24-Channel Digital Input/Output Card

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  • 24 channels of TTL digital I/O lines.
  • All I/O lines buffered by tristate transceivers.
  • Outputs sink 24mA and source 15mA.
  • Four- and eight-bit groups independently selectable for I/O.
  • Pull-up resistors to provide CMOS and contact closure compatibility.
  • Cable crosstalk suppression by grounds on all even-numbered conductors.
  • 50-pin connector for compatibility with Western Reserve Controls, Opto-22, Gordos, Potter and Brumfield, etc.
  • External interrupts.
  • Designed, made, supported, and manufactured in the USA
Last updated on October 20, 2023, 9:11 am


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The IOD-24 is a 24-bit half-size card. A Programmable Peripheral Interface chip, type 8255-5 provides three 8-bit ports (A, B, and C). Each port can be independently programmed for either input or output. Port C can also be configured as two 4-bit ports. These cards fully implement Mode 0 of the 8255 PPI chip. (Consult the factory if you desire to operate in Mode 1.) Type LS245 bi-directional transceivers sink 24 mA (optionally 64 mA) and source 15 mA. These transceiver buffers provide hysteresis correction on inputs and added drive capability on outputs. The direction of the transceivers is set by software.

Input/Output connections to IOD-24 are via a 50-pin connector on the mounting bracket.  Units required to meet EU “CE” requirements are supplied with blank mounting brackets. That permits you to use cabling method’s that best fit your application.Strain relief is provided for these cables. Ready-made displacement type ribbon cables are available from ACCES as p/n CAB50F-xx. Alternate wires are connected to ground to provide shielding and minimize crosstalk.

Two of the I/O lines can be used for User Interrupts; one line to enable/disable this function and one for the external interrupt signal. Interrupt levels 2-7 are selected by jumper on IOD-24.

Card I/O bus address selection is by DIP switches on the cards. The address can be anywhere in I/O space. On power-up or reset, all ports are automatically configured as inputs. This prevents spurious outputs. Before use, of course, each PPI should be software configured by writing to its control register.




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.

Digital Inputs

  • Logic High: 2.0 to 5.0 VDC
  • Logic Low: -0.5 to 0.8 VDC
  • Input Load (Hi): +20 microamperes
  • Input Load (Lo): -200 microamperes

Digital Outputs

  • Logic High: 2.5 VDC min.,source 15 milliamperes
  • Logic Low: 0.5 VDC max., sink 24 milliamperes (64 milliamperes optional)

DC Power Output

  • +5 VDC computer power. 1A fuse included on IOD-24.


  • Power Required: +5 VDC, 200mA,
  • Size: 5.0″ Long (12.7cm),
  • Operating Temperature Range: 0o to 60 oC
  • Storage Temperature Range: -50o to 120 oC
  • Humidity: 0 to 90% RH, non-condensing

Regulatory Compliance

  • This product is in full compliance with CE requirements.
  • MOQ’s may be required.
ModelDescriptionPrice (USD)

24 TTL DIO ISA card