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ISA Bus Change-Of-State Detecting Digital I/O Card


  • 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
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.

Available Reference Manuals

Available Software Downloads

Drivers and Downloads

Full 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.

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.

ModelPrice (USD)

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