User`s guide

Chapter 3

Functional Details

82C55 emulation

The PCIe-DIO24 emulates the 82C55 Programmable Peripheral Interface (PPI) chip. Measurement

Computing's Universal Library and Windows driver supports mode 0 only.

Whenever the board is powered on or reset, all pins are set to high-impedance input. Based on standard TTL

functionality, these inputs typically float high, and may have enough drive current to turn on external devices.

Consequently, if you have output devices such as solid state relays, they may be switched on whenever the

computer is powered on or reset. To prevent unwanted switching, and to drive all outputs to a known state after

power on or reset, configure each port resistor with InstaCal.

Unconnected inputs float to the pull direction

Unconnected inputs will float in the pull direction that is configured for the port with InstaCal (either up/high or

down/low).

Replacing a fuse

The PCIe-DIO24 has two individual 0.375 amp slow blow fuses. One fuse is connected to the 12V output at pin

16, and is labeled

F7 on the board. The second fuse is connected to both +V

DIO

outputs at pin 18 and pin 20, and

is labeled

F6 on the board. A spare fuse is installed on the board at location F4. All fuses are secured to the

board with clips for convenient replacement.

A fuse will blow during operation if amperage exceeds 0.375 amp. If you need to replace a fuse, perform the

following procedure.

1. Hold the center of the blown fuse and pry it from the fuse holder clip.

2. Insert the replacement fuse into the fuse holder clip.

Fuse specifications

Refer to the information below to purchase additional fuses, if required:

 Manufacturer: LittelFuse®

 Type: 452 Series NANO

2®

Slo-Blo

Subminiature Surface Mount Fuse

 Part number: 0452.375

 0.375 amp, 125 volts, 1.2 Ω

Logic level switch

Use switch S1 to set the logic level for either 3.3V or 5V (default). The switch is located above the I/O

connector (see Figure 2 on page 9).

Figure 5. Logic level select switch

3.3V