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Products   >   I/O Expansion Modules   >   Digital I/O Modules   >   Onyx-MM-DIO Digital I/O Module

Onyx-MM-DIO Digital I/O Module

Low-Cost 48-Line Digital I/O PC/104 Module

Onyx-MM-DIO Digital I/O Module: I/O Expansion Modules, Wide-temperature PC/104, PC/104-<i>Plus</i>, PCIe/104 / OneBank, PCIe MiniCard, and FeaturePak modules featuring programmable bidirectional digital I/O, counter/timers, optoisolated inputs, and relay outputs., PC/104
Digital I/O Operation
Free Software
I/O Header Pinout
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If you're looking for a basic 48-line digital I/O PC/104 module, then Onyx-MM-DIO is what you need. This module is the same as our Onyx-MM digital & counter/timer module but without the counter/timer and interrupt circuitry. This board still has the quality and attention to detail of our other modules, such as: 10K Ohm pull-up resistors on all I/O lines; all ports reset to 0 on power-up or system reset; connector pinouts compatible with our other digital I/O boards; and free software.

The 48 digital I/O lines on Onyx-MM-DIO are based on 2 82C55 ICs. They can be programmed for input or output in groups of 8 lines. Direct as well as strobed (latched) I/O modes are supported, and all I/O lines are connected to 10K Ohm pull-up resistors.

Digital I/O Operation

Onyx-MM-DIO has 48 digital I/O lines using 2 82C55 ICs. Each chip has 24 I/O lines organized as three 8-bit ports, A, B, and C. All I/O lines are connected to 10KOhm pull-up resistors, and on power-up or system reset, all ports reset to input and are pulled high. A control register on the 82C55 chip allows you to program each port for input or output and for different operating modes, including basic I/O, strobed I/O, and bit set/reset.

Mode 0 operation provides basic input and output operations. No handshaking signals are used. This is the most common method of digital I/O and is useful for reading status signals, turning switches on and off, etc. All three ports can operate in Mode 0.

Mode 1 operation provides strobed I/O on ports A and B with handshaking signals provided on port C. In input mode, one signal is a strobe to latch data into the port, and a second signal is an acknowledge output. In output mode, one signal is used to indicate that the CPU has written new data to the port, and a second signal is an acknowledge input.

Mode 2 operation allows the use of Port A as a bidirectional data bus, with port C lines used for handshaking. Port A is normally in tristate mode. When the CPU writes new data to port A, an output signal indicates new data is available. In response, the external circuit strobes an acknowledge input signal, thereby enabling the output buffers on Port A. The external circuit can also latch new data into Port A with an input data strobe signal.

Bit set/reset mode enables individually setting (1) or resetting (0) any bit on Port C without having to read Port C and worry about masking or protecting unaltered bits. Note: The driver software shipped with Onyx-MM-DIO allows you to easily perform bit set and reset operations on any bit of any port.

Free Software

Onyx-MM-DIO comes with free driver software compatible with C and Basic languages. Example programs are included to get you started quickly. Some examples of the supported board operations are:

  • Digital input, bit, byte, and word
  • Digital output, bit, byte, and word
  • Interrupt-driven digital I/O with external trigger

I/O Header Pinout

Onyx-MM-DIO has two identical 50-pin I/O headers with 24 digital I/O lines on each header.

(Port A) A7 1 2 Ground
A6 3 4 Ground
A5 5 6 Ground
A4 7 8 Ground
A3 9 10 Ground
A2 11 12 Ground
A1 13 14 Ground
A0 15 16 Ground
(Port C) C7 17 18 Ground
C6 19 20 Ground
C5 21 22 Ground
C4 23 24 Ground
C3 25 26 Ground
C2 27 28 Ground
C1 29 30 Ground
C0 31 32 Ground
(Port B) B7 33 34 Ground
B6 35 36 Ground
B5 37 38 Ground
B4 39 40 Ground
B3 41 42 Ground
B2 43 44 Ground
B1 45 46 Ground
B0 47 48 Ground
+5V 49 50 Ground

In 0 1 2 In 1
Gate 0 3 4 Gate 1
Out 0 5 6 Out 1
In 2 7 8 External Interrupt
Gate 2 9 10 Ground
Out 2 11 12 Ground
+5V 13 14 Ground


Digital I/O
Chip 82C55A (qty. 2)
Number of I/O lines 48
Direction Programmable in groups of 4 or 8
Input voltage
Low: -0.5V min, 0.8V max
High: 2.0V min, 5.5V max
Output voltage
Low: 0.0V min, 0.4V max
High: 3.0V min, Vcc -0.4V max
Output current ±2.5mA max, each line
Pullup resistors 10KΩ all input lines
Power supply +5V ±10% @ 100mA typical, all outputs open
Temperature -40°C to +85°C
PC/104 Bus 8 bits
Weight 2.3 oz/65g
MTBF OMM-DIO-XT 1,714,901 hours
RoHS Compliant
48 digital I/O lines
Programmable port directions
10KΩ pull-up resistors on each line
All lines power up in input mode
Dual 50-pin I/O headers
Low cost
Software and technical manual included
-40°C to +85°C extended temperature
Customers who use this product also use:
50-pin Data Acquisition Cable

This product can be customized and ruggedized. Click here for more information.
See Onyx-MM-DIO Digital I/O Module Technical Resources
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Onyx-MM-DIO Datasheet
(.pdf, 93.3 kb)
Onyx-MM-DIO Manual v1.4
(.pdf, 337.5 kb)

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Onyx-MM-DIO Digital I/O Module
available models:
Onyx-MM 48 Digital I/O only Extended Temperature
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Cables and accessories
available models:
50-conductor .1" pitch 18" ribbon cable, Data acquisition Cable (uses 2)
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VDC 2006 Platinum Vendor Award