104-DIO-48S and 104-DIO-24S

Change-Of-State Detecting Digital I/O Cards


  • 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

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.

Drivers and Downloads

List of available Downloads: Software Packages, Drivers, Manuals, and other documents

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.

Available Reference Manuals

Available Software Downloads

Available Datasheets

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 +85C 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.

ModelPrice (USD)

Acquisition, Control, Communication: Engineering and Systems

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