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ISA Bus Digital Input/Output Card


  • 64 channels of digital I/O
  • Eight 8-bit ports of directly addressable bi-directional I/O
  • Bit-by-bit programmable for input or output
  • I/O buffers can be enabled/disabled under program control
  • Compatible with industry standard I/O racks from Opto-22, Western Reserve Controls, DuTec, Gordos, Potter & Brumfield, etc
  • User selectable to occupy any eight consecutive I/O addresses.
  • Control and I/O ports separately addressable to allow I/O ports for multiple cards to occupy consecutive addresses
  • Four inputs may be directed to hardware interrupts
  • Designed, made, supported, and manufactured in the USA
Model IOD-64 accepts up to 64 bits of Digital I/O and the card is organized into eight 8-bit ports. Input voltages can range up to 30 VDC. This card is particularly useful for interface between an ISA-Bus computer and industry-standard, optically-isolated, solid-state I/O module mounting racks. Up to four 16-position I/O racks can be controlled and each point is directly addressable by the host computer.

Variable I/O-mapped addressing allows you to select eight consecutive addresses plus a separate control port from any I/O addresses between 200 hex and 3FF hex. In addition, you can drive four of the host's interrupts from inputs applied to IOD-64. Read/Write Select Logic manages all data transmission between the computer and the I/O ports. There are five inputs to the select logic:

  • Reset: When this line goes high, either on power-up or during a low-line voltage loss, it clears the Output Control Latch disabling all output ports. This assures that there will be no spurious outputs.
  • Address Enable (AEN): When this line is driven low, it enables the PC I/O channel. The Read/Write Select Logic then checks the value on the address bus by comparing that address to the I/O Port and Control Addresses.
  • I/O Write Command (IOW): When this line is low and the address comparison is true, the IOD-64 card reads data from the data bus.
  • I/O Read Command (IOR): When this line is low and the address comparison is true, the IOD-64 card writes data to the data bus.
  • Address (ADDR): These ten lines are used to address the Control Port and I/O Ports.

When the Data Bus Buffer is enabled by the Read/Write Select Logic, it permits data transfer between the host computer and the IOD-64. The Output Control Latch disables any or all of the eight 8-bit I/O ports. Inputs to the Output Control Latch are:

  • Data from the host computer data bus.
  • When the PC-Reset line is high, it automatically clears the Output Control Latch which, in turn, disables all outputs as previously described.
  • When the Output Control Latch is enabled by the Read/Write Select Logic, it will disable individual ports as required by programming.

The IRQ Control, when enabled by the Read/Write Select Logic, routes external inputs received from any or all of the last four inputs of PORT 7 to IRQ4 through IRQ7 of the host computer.


Four 50-pin headers are provided; one for each group of 16 bits. Sixteen bi-directional data lines are alternated with 16 ground lines on each connector. Also, +5 VDC power is available and digital ground.

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.


Digital Inputs

  • Logic High: 2.0 to 30 VDC
  • Logic Low: -0.5 to 0.8 VDC
  • Input Load (Hi): +20 uA
  • Input Load (Lo): -200 uA

Digital Outputs

  • Logic High: 2.5 VDC min. to 30.0 VDC (w/ external pull-ups), source 15 mA
  • Logic Low: 0.5 VDC max., sink up to 40 mA

Power Output

  • +5 VDC from computer bus (external 1A fast-blow fuse recommended)


  • Power Required: +5 VDC at 450 mA typical
  • Size: 13.1 inches long
  • 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.

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