104-DIO-48S Digital I/O Board w/CoS IRQ

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  • 48 or 24 parallel lines of 82C55 digital I/O with tristate buffers prevent unintended control of external equipment
  • IRQ on input change of state (COS) eliminates the need for constant polling
  • High sink/source current 64mA/32mA
  • I/O pulled up to 5V for contact monitoring
  • Compatible with Opto-22 and other industry standard I/O racks

Factory Options: (call for pricing and availability)

  • 82C54 with three 16-bit counter/timers for event counting, frequency output, pulse width and frequency measurement
  • 0 to 70°C and -40 to +85°C versions available
  • Economy version without COS feature
  • Pull-down resistors on I/O lines
  • RoHS Available. Please contact us for ordering information
Last updated on April 19, 2024, 8:15 am


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Change-Of-State Detecting Digital I/O Cards

Digital I/O

The circuits use an 82C55A PPI with mode 0 supported. Ports A, B, C High, and C Low are buffered with 74ABT245 transceivers and pulled up to 5V.

COS Detection

Change of State Detection allows the card to generate an interrupt, port by port. Either direction will set the change of state interrupt. Your application can run much smoother by using this feature as processor overhead is greatly reduced, polling is not required.


The optional 82C54 has three-sixteen bit counters within one chip. These counters are useful for making frequency outputs, measuring frequency of square waves, pulse width outputs, pulse width measurements etc.
The 104-DIO-48S is supported in most operating systems and include a free DOS, Linux and XP/2003/2008/7/8/8.1 compatible software package. This includes sample programs and source code in “C” and Pascal for DOS, and Visual Basic, Delphi, and Visual C++ for Windows. Also included is a graphical setup program in Windows.


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.

Digital I/O

  • Programmable Peripheral Int.: 82C55A
  • Channels: 24 or 48, pulled up to 5V via 10K
  • Buffered Channels: 24 or 48 bits (ports A, B, C-High and C-Low)
  • Sink & Source Current: 64mA & 32mA
  • Modes supported: Mode 0
  • Change of State Detection: 48 Inputs (both 8255 groups, all 8 ports)
  • Throughput: Up to 1 MByte/sec
  • Power Output: Resettable fused +5V @ 500mA per 50 pin connector


  • Peripheral Interface Timer: Type 82C54
  • Counters: 3 x 16-Bit down counters
  • Clock Frequency: 1 MHz Time Base, available to the user
  • Software Support: Event Counter, Frequency Output, Frequency and Pulse Measurement
  • Max Input Frequency: 10MHz
  • Signal Type: TTL


  • Power Required: +5V @50mA Typical
  • Operating temperature: 0°C to +70°C, optionally -40°C to +85°C available
  • Storage temperature: -50° to +120°C
  • Interrupt Requests: Eleven channels, IRQ 3-7, 9-12, 14, 15
  • Interrupt Status Registers: Two; One 8bit for COS, One single bit for C/T

CE testing & approval must be done at the system level, in the designed enclosure, and is not done on individual boards.

ModelDescriptionPrice (USD)

24-bit, Digital Input/Output with Change of State Detect PC/104 Board


48-bit, Digital Input/Output with Change of State Detect PC/104 Board

Cable Connectivity
CAB50F-6 Cable, Ribbon, 50-pin Female to Female, 6 feet
C104-50F-12 Cable, Ribbon, 50-pin Female to Female, 1 foot
STB-50 DIN-rail mountable screw terminal board for 50 pin header type connector
STB-48CH External screw terminal board for 26 to 12 AWG wire and remote wiring
Relays and Signal Conditioning
CAB50F-6 Cable, Ribbon, 50-pin Female to Female, 6 feet
IIB-24 24-channel optical isolator board for each 50-pin header
ROB-24 24 SPDT (DPDT optional), Form C Relays board for each 50-pin header