Chapter 8

Digital I/O

The voltage input and output levels and the current drive levels of the DIO lines are listed in the specifications of your device.

Static DIO

You can use static DI and DO lines to monitor or control digital signals.

All samples of static DI lines and updates of DO lines are software-timed.

I/O Protection

Each DI, DO, and PFI signal is protected against overvoltage, undervoltage, and overcurrent conditions as well as ESD events. However, you should avoid these fault conditions by following these guidelines.

•Do not connect a DO or PFI output lines to any external signal source, ground signal, or power supply.

•Understand the current requirements of the load connected to DO or PFI output signals. Do not exceed the specified current output limits of the DAQ device. NI has several signal conditioning solutions for digital applications requiring high current drive.

•Do not drive a DI or PFI input line with voltages outside of its normal operating range. The PFI or DI lines have a smaller operating range than the AI signals.

Increasing Current Drive

The total internal current limit for digital outputs and power down from the +5 V terminals is 50 mA. You can increase this internal current limit by supplying an external +5 V supply. Refer to the +5 V Power as an Input section of Chapter 3, Connector Information.