Manual 104-IIRO-8(E)
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Chapter 1: FUNCTIONAL DESCRIPTION
This board provides isolated input, digital inputs and relay output interface for PC/104 compatible computers.
The board provides eight each optically-isolated inputs for AC or DC control signals, digital TTL compatible
inputs and electromechanical relay outputs. The board occupies four consecutive addresses in I/O space. Read
and write operations are done on an 8-bit-byte oriented basis. Two models are available, the basic model
includes Change of State Detection (COS) which will flag an interrupt, while the E model doesn’t include COS
detection or use interrupts.
INPUTS
The isolated inputs can be driven by either AC or DC signals and are not polarity sensitive. Input signals are
rectified by photocoupler diodes. A 1.8K-ohm resistor in series dissipates unused power. Standard 12/24 AC
control transformer outputs can be accepted as well as DC voltages. The input voltage range is 3 to 28 volts
(rms). External resistors connected in series may be used to extend the input voltage range.
Each input circuit contains a switchable slow/fast filter that has a 4.7 millisecond time constant. (Without filtering,
the response is 10 uSec.) The filter must be selected for AC inputs in order to eliminate response to zero
crossings. The filter is also valuable for use with slow DC input signals in a noisy environment. The filter may be
switched out for DC inputs in order to obtain faster response. Filters are individually selected by jumpers. The
filters are switched into the circuit when the jumpers are installed in position FLT0 to FLT7.
Eight digital inputs are available for digital applications. Inputs are TTL compatible and include 10K pullup
resistors.
INTERRUPTS
When enabled by a software read to base a2 (and when a jumper is installed to select one of the
interrupt levels IRQ2-7, IRQ10-12, and IRQ14-15), the board asserts an interrupt whenever any of the inputs
changes state from low to high or high to low. This is called Change-of-State (COS) detection and greatly frees
up computer resources by eliminating the need for constant polling to determine when an input has changed.
Once an interrupt has been generated and serviced, it is cleared automatically after 2 usec.
This interrupt capability may be disabled by a software write to base a2. It may be re-enabled with a
read to base a 2. (Basic model only)
OUTPUTS
The electromechanical relay outputs are comprised of eight FORM C SPDT outputs. The relays are all de-
energized at power-on. Data to the relays are latched by a write to the base address.
