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Eight Isolated Digital Inputs and Eight Relay Outputs


  • Eight optically isolated, non-polarized digital inputs
  • Eight electromechanical relay outputs
  • 60V isolation
  • Can detect input state change and assert interrupt

IIRO-8 is a low-cost, half-size card that provides isolated input and output interface for PC/XT/AT and compatible computers. The card provides eight optically-isolated inputs for AC or DC control signals and eight electromechanical relay outputs. Inputs are optically isolated from each other and from the computer. They can be driven by either AC or DC signals and are not polarity sensitive. Thus inputs can be driven from standard 12/24 VAC control transformers as well as by DC voltages. Input voltage range is 5 to 24 Volts (rms). External resistors connected in series can be used to extend this input range.

Each input circuit contains a switchable slow/fast filter that has a 10 millisecond time constant. The filter must be selected for AC inputs but may be switched out in order to obtain faster response for DC inputs. The filter is also useful for slowly-changing noisy DC inputs. A DIP switch on the card permits filter selection on a channel-by-channel basis. Alternatively, you can globally switch all filters in or out under software control.

Another feature of this card is the ability to detect if a state change occurs at any one or more of the inputs and, in turn, assert an interrupt. This is very useful when monitoring for contact closures/openings because it is not necessary to continuously poll the inputs. When the IIRO-8 detects a state change, the resulting interrupt request can be used to initiate a poll of the inputs to determine which line(s) changed. After the interrupt has been serviced, the interrupt latch can be cleared by a software write.

The electromechanical relay outputs are comprised of five Form C SPDT outputs and three Form A SPST (normally open) type. On/Off status of the relays can be read back. All relays are de-energized at power turn-on. IIRO-8 occupies four consecutive addresses in I/O space. The base address can be selected anywhere within the address range 000-3FF (hex). Read and write operations are done on an 8-bit byte-oriented basis. All input/output connections are via a single 37-pin D connector at the rear of the card.



Digital Inputs

  • Number of inputs: 8
  • Type: Non-polarized, optically isolated from each other and from the computer. (not TTL/CMOS compatible)
  • Voltage Range: 5 to 24V DC or AC (50 to 1000 Hz)
  • Isolation: 60V channel-to-ground or channel-to-channel
  • Input Resistance: 470 ohms in series with two diodes and an LED
  • Response Time: 20 mSec w/filter, 10 uSec w/o filter

Relay Outputs

  • Number of outputs: 8
  • Contact Rating: 2A carry current, bifurcated, gold clad, silver palladium
  • Contact Arrangement: Channels 0-4 are SPDT Form C and channels 5-7 are SPST Form A
  • Contact Rating: Initial 100 milliohms maximum
  • Contact Life: mech'l: 5 million operations minimum; elect'l: 500,000 operations minimum at full load
  • Operating Time: 2 milliseconds maximum
  • Release Time: 1 milliseconds maximum


When enabled by software and by installation of level-select jumpers, interrupts are generated when digital inputs change state.

Power Required

5VDC @ 1 A (all relays ON)


  • Ambient Temperature: Operating: 0 to 50 C
  • Storage: -20 to 70 C
  • Humidity: 0 to 90 percent (non-condensing)
  • Weight: Approx. 8 oz.

Part NumberPrice(USD)
View / Download Manual (in .pdf format)
Acquisition Control Communications Engineering / Systems
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