Chapter 8
PFI
8-6
ni.com
I/O Protection
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.
Programmable Power-Up States
At system startup and reset, the hardware sets all PFI and DIO lines to
high-impedance inputs by default. The DAQ device does not drive the
signal high or low. Each line has a weak pull-down resistor connected to it,
as described in the specifications document for your device.
NI-DAQmx 7.4 and later supports programmable power-up states for PFI
and DIO lines. Software can program any value at power up to the P0, P1,
or P2 lines. The PFI and DIO lines can be set as:
•
A high-impedance input with a weak pull-down resistor (default)
•
An output driving a 0
•
An output driving a 1
Refer to the
NI-DAQmx Help
or the
LabVIEW Help
in version 8.0 or later
for more information about setting power-up states in NI-DAQmx or MAX.
Note
When using your M Series device to control an SCXI chassis, DIO lines 0, 1, 2, and
4 are used as communication lines and must be left to power-up in the default
high-impedance state to avoid potential damage to these signals.
