IOD-48S 48-Channel ISA Bus Change-of-State Detecting Digital I/O Card

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  • 48 parallel digital I/O lines
  • Can generate interrupts when inputs change
  • All 48 I/O lines buffered by transceivers on the card
  • Pull-up resistors for CMOS and contact closure inputs
  • Four- and eight-bit ports independently selectable for I/O
  • Crosstalk suppression by grounds on all even-numbered cable conductors
  • 50-pin connector for compatibility with industry standard I/O mounting racks
  • Designed, made, supported, and manufactured in the USA


  • Automatic Test Systems
  • Laboratory Automation
  • Robotics
  • Machine Control
  • Security Systems, Energy Management
  • Relay Monitoring and Control
  • Parallel Data Transfer to PC
  • Sensing Switch Closures or TTL, DTL, CMOS Logic
  • Driving Indicator Lights or Recorders
Last updated on November 2, 2023, 6:31 pm


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This seven-inch card is for use in PC/XT/AT-class computers and contains two independent 24-bit groups. Two 50-wire ribbon interface cables plug into headers on the card and exit through a slot in the back-plate. Units required to meet EU “CE” requirements are supplied with blank mounting brackets. This permits using cabling methods that best fit your applications. Each 24-bit group uses a Programmable Peripheral Interface chip type 8255-5 (PPI). Each PPI, in turn, provides three 8-bit ports (Ports A, B, and C) which can be independently configured for either input or output. Port C can also be configured in four-bit groups for input or output. Type 74LS245 tri-state transceivers provide hysteresis correction for inputs and added drive capability for outputs. The direction of these buffers is automatically set as input or output according to software command. Also, the tri-state transceivers can be enabled or disabled under software control.

This card fully implements Mode 0 of the PPI. The card cannot be used in Mode 1 or Mode 2. A major feature of this card is that the state of all inputs can be monitored and, if any one or more bits change, a latched interrupt request can be generated. Thus, you can detect input state changes without need for software to continuously poll the inputs. After the interrupt has been serviced, the interrupt latch can be cleared by a software write. This change-of-state detection is particularly useful in robotics applications.

Interrupts are OR’ed together and may be directed to any “AT” interrupt level by jumper selection. IOD-48S occupies 16 bytes of I/O address space. The base address is set by DIP switch on the card and is selectable anywhere in the range of 000 to 3FF hex.




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.


  • 48 buffered digital I/O lines
  • Latched change-of-state interrupt on up to 48 I/O lines
  • Hysteresis on input lines improves noise margin
  • Pull-ups on I/O lines for CMOS and contact-closure compatibility
  • Tri-state transceiver buffers prevent erroneous outputs at power-up

Digital Inputs

  • Logic High: 2.0 to 5.0 V DC.
  • Logic Low: -0.5 to +0.8 V DC.
  • Input Load (Hi): 20 uA.
  • Input Load (Lo): -200 uA.

Digital Outputs

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


  • Operating Temperature: 0 to +60 degree C.
  • Storage Temperature: -50 to +120 degree C.
  • Humidity: 0% to 90% non condensing.
  • Size: 7.15 inches. Install in a half-length slot.

Power Requirements

  • Input: +5 VDC at 300 mA typical
  • Output: +5 VDC from computer bus (ext. 1A fast-blow fuse recommended).

Regulatory Compliance

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

48 TTL DIO ISA card, with CoS detection