Chapter 6 Digital I/O
© National Instruments Corporation 6-5 NI USB-621x User Manual
Figure 6-3 shows the circuitry of one DIO line. Each DIO line is similar.
The voltage input and output levels and the current drive levels of the DIO
lines are listed in the NI USB-621x Specifications.
Figure 6-3. USB-6212/6216 Digital I/O Circuitry
The following sections provide information about the various parts of the
DIO circuit.
Static DIO on USB-6212/6216 Devices
Each of the USB-6212/6216 DIO lines can be used as a static DI or DO
line. You can use static DIO lines to monitor or control digital signals.
Each DIO can be individually configured as a digital input (DI) or digital
output (DO).
All samples of static DI lines and updates of DO lines are software-timed.
I/O Protection on USB-6212/6216 Devices
Each DIO 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:
•If you configure a PFI or DIO line as an output, do not connect it to any
external signal source, ground signal, or power supply.
• If you configure a PFI or DIO line as an output, understand the current
requirements of the load connected to these 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.
•If you configure a PFI or DIO line as an input, do not drive the line with
voltages outside of its normal operating range. The PFI or DIO lines
have a smaller operating range than the AI signals.
• Treat the DAQ device as you would treat any static sensitive device.
Always properly ground yourself and the equipment when handling the
DAQ device or connecting to it.
Digital Line Direction Control
Static DI
I/O Protection
Weak Pull-Down
P0.x
Static DO
Buffer
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