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Products   >   Services   >   End-of-Life Products   >   Garnet-MM Digital I/O PC/104 Module
48 lines of TTL digital I/O
Programmable port directions
High-current outputs: +15/-64mA per line
OPTO22 interface compatible
Dual 50-pin I/O headers
2 PC interrupt lines
Software and technical manual included
See Garnet-MM Digital I/O PC/104 Module Technical Resources
Request Product information
Request Technical Support
Garnet-MM Datasheet
(.pdf, 72.5 kb)
Garnet-MM Manual v1.4
(.pdf, 420.2 kb)
82C55 Digital I/O IC Datasheet
(.pdf, 275.4 kb)
Garnet-MM Example Programs for UD 5.91
(.zip, 309.9 kb)
Universal Driver Software

End of Life Product, product only available as Minimum Order Quantity Product
For replacement product see GPIO-MM

Garnet-MM Digital I/O PC/104 Module

48-Line High Current Digital I/O PC/104 Module

Garnet-MM Digital I/O PC/104 Module
click for a larger image
High-Current Capability
Free Software
I/O Headers


Garnet-MM is a PC/104-format digital I/O board with 48 lines of I/O. It contains two 82C55 ICs, each having 3 8-bit I/O ports. Each 82C55 has its own 50-pin I/O header for external connections. Direction on all ports is selected by programming control registers built in to the 82C55 chips.

All I/O lines are buffered with transceivers, whose directions are controlled by logic which responds to the direction control values written to the 82C55s. Each line is capable of sourcing 35mA in a logic low state or sinking 6mA in a logic high state. The board is constructed entirely with CMOS logic to reduce power consumption and requires only +5V for operation.

Garnet-MM's I/O headers are organized to allow direct interfacing to OPTO-22's isolated I/O racks, including the G4 series, the PB16-H, -J, -K, -L, PB8H, and the PB24HQ. These racks and I/O modules allow up to 3000 VRMS isolation between the computer and the user's signals. All control signals, power, and ground on the Garnet-MM I/O header match the corresponding signals on these I/O racks, so a single 50-pin ribbon cable, such as Diamond Systems' C50-3, is all that is needed to make the connection.

The board provides access to interrupt levels 2-7 on the PC bus for real-time background applications. Interrupts can be generated in two ways. In Mode 0 operation, a rising edge on one of four interrupt lines causes the board to generate an interrupt request on the bus. In Mode 1 operation, the 82C55 generates interrupts in response to handshake signals between Garnet-MM and external circuitry.

Software drivers are included with Garnet-MM to allow controlling the board from Microsoft C, QuickC, GW-Basic, and QuickBasic languages. The software driver supports all of the board's features, including interrupt operation. Example programs demonstrate the use of the function calls and provide a starting point for program development.

High-Current Capability for Solid State Relays

Garnet-MM was specifically designed for applications that use mechanical or solid state relays, such as the OPTO22 G4 series. These devices typically require more drive current than many digital I/O cards can supply. For example, an OPTO22 output module requires 12mA of drive current, whereas a typical 82C55-based digital I/O card can only supply 2.5mA. However, all output lines on Garnet-MM have high-current buffers capable of driving up to 64mA each when low and 15mA each when high. This is enough for solid state relays and many mechanical relays as well. These output buffers change direction automatically in response to the direction control bytes written to the board. In addition, power and ground for the rack are provided straight from the board's I/O header, along with the data lines needed to read from and write to the relays.

Free Software

Garnet-MM 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

I/O Header Pinout

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


Digital I/O
Chip 82C55 (qty. 2)
Number of I/O lines 48
Direction Programmable in groups of 4 or 8
Input voltage
Low: -0.0V min, 0.8V max
High: 2.0V min, Vcc max
Output voltage
Low: 0.0V min, 0.55V max
High: 2.0V min, Vcc -0.3V max
Output current
Logic 0: 64mA max per line
Logic 1: 15mA max per line
Output drivers 74F245/74F243
Power supply +5V ±10% @ 160mA typical
Temperature 0° to +70°C
PC/104 Bus 8 bits
Weight -24: 2.7 oz/76g
-48: 3.0 oz/85g

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Garnet-MM Digital I/O PC/104 Module
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Garnet-MM 48-line High-current Digital I/O Minimum Order Quantity of 50
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