Chapter 6
Digital I/O
©
National Instruments
6-23
X Series User Manual
I/O Protection
Each DIO and PFI signal is protected against overvoltage,
u
ndervoltage,
and overc
u
rrent conditions as well as ESD events. However, yo
u
sho
u
ld
avoid these fa
u
lt conditions by following these g
u
idelines:
•
If yo
u
config
u
re a PFI or DIO line as an o
u
tp
u
t, do not connect it to any
external signal so
u
rce, gro
u
nd, or power s
u
pply.
•
If yo
u
config
u
re a PFI or DIO line as an o
u
tp
u
t,
u
nderstand the c
u
rrent
req
u
irements of the load connected to these signals. Do not exceed the
specified c
u
rrent o
u
tp
u
t limits of the DAQ device. NI has several signal
conditioning sol
u
tions for digital applications req
u
iring high c
u
rrent
drive.
•
If yo
u
config
u
re a PFI or DIO line as an inp
u
t, do not drive the line with
voltages o
u
tside of its normal operating range. The PFI or DIO lines
have a smaller operating range than the AI signals.
•
Treat the DAQ device as yo
u
wo
u
ld treat any static sensitive device.
Always properly gro
u
nd yo
u
rself and the eq
u
ipment when handling
the DAQ device or connecting to it.
Programmable Power-Up States
At system start
u
p and reset, the hardware sets all PFI and DIO lines to
high-impedance inp
u
ts by defa
u
lt. The DAQ device does not drive the
signal high or low. Each line has a weak p
u
ll-down resistor connected to it,
as described in the specifications doc
u
ment for yo
u
r device.
NI-DAQmx s
u
pports programmable power-
u
p states for PFI and DIO lines.
Software can program any val
u
e at power
u
p to the P0, P1, or P2 lines. The
PFI and DIO lines can be set as:
•
A high-impedance inp
u
t with a weak p
u
ll-down resistor (defa
u
lt)
•
An o
u
tp
u
t driving a 0
•
An o
u
tp
u
t driving a 1
Refer to the
NI-DAQmx Help
or the
LabVIEW Help
for more information
abo
u
t setting power-
u
p states in NI-DAQmx or MAX.
Note
When
u
sing yo
u
r X Series device to control an SCXI chassis, DIO lines 0, 1, 2, and
4 are
u
sed as comm
u
nication lines and m
u
st be left to power-
u
p in the defa
u
lt
high-impedance state to avoid potential damage to these signals.
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