Digital I/O Overview
Digital I/O Overview
Digital input/output (DIO) devices are used in a wide variety of
applications from automotive design, industrial factory automation,
and machine control, to aerospace, laboratory research, and
biomedical applications. You can connect NI digital I/O devices to
limit and proximity switches, photoelectric sensors, level gauges,
pressure switches, gas detectors, pumps, motors, solid-state relays,
electromechanical relays, digital data buses, and more.
NI DIO devices can be installed in traditional desktop computers
using the PCI or ISA bus, connected via USB port, or installed in laptop
computers with PCMCIA slots. For the utmost in reliability and
mechanical ruggedness, NI also offers PXI digital I/O devices suitable for
operation in the LabVIEW Real-Time environment.
ER-8 and ER-16 accessories and eight channel SC-2062 enclosure are
available. Refer to Table 3 for signal conditioning accessory catalog
page numbers.
NI 653x
High-Speed
DIO (p.432)
✓
✓
✓
Product Families
NI 6527
NI 650x
Isolated
Low-Cost
DIO (p. 377)
DIO (p. 379)
✓
✓
–
–
–
✓
1
Application
Perform basic digital I/O
Transfer data with fixed
timing between points
Transfer data where both
the device under test and
measurement device can
pause the transfer
Run a user-defined software Change Notification
routine when a user-defined and Pattern Matching
DIO event occurs
1
Handshaking
Mode of Operation
Software
timed
Hardware
timed
Handshaking
I/O
✓
✓
✓
Choose Your Digital I/O Hardware
Isolation
Isolation physically and electrically separates two parts of a circuit
and provides several advantages. It breaks ground loops, improves
common-mode voltage and noise rejection, and it permits two
parts of the circuit to be at different voltage levels. Isolation
protects both computer circuitry and human operators. Industrial
applications often require isolation to protect the electronics from
transient voltage spikes and to provide greater common-mode noise
rejection in electrically noisy environments containing machinery
and inductive loads.
In the case of channel-to-channel isolated I/O, each channel has its
own ground terminal. In bank-to-bank isolated devices, each bank
(or group) consists of several channels that share the same ground
but are isolated from other banks. NI 6527 devices provide 60 VDC
of built-in channel-to-channel isolation between each I/O channel.
supplied by the 8255; only one handshaking mode is available. See individual product details on the following
pages for more information. See page 376 for details.
Table 2. Digital I/O Applications.
Tech Tip
Q: I would like to perform high-speed buffered digital I/O controlled
by an external or internal digital clock or handshaking signal. Which
digital I/O device do you recommend?
A: For high-speed buffered pattern I/O or handshaking I/O, see the
hardware-timed NI 653x devices on page 432.
Accessory
SCXI
SSR Series
SC-206x
ER-8/16
CA-1000
SCB-100
CB-50
CB-50LP
CB-100 kit
Description
Signal conditioning system
Digital signal conditioning modules
Digital signal conditioning modules
Electromechanical relays
Configurable connector accessory
Shielded connector block
I/O connector block
I/O connector block
I/O connector block kit; includes cable
Page
270
321
349
349
351
382
382
383
383
Data Acquisition and
Signal Conditioning
Signal Conditioning
For even higher isolation levels, NI 650x devices can be connected to
SCXI-116x signal conditioning modules to provide 450 V
rms
of bank-
to-bank isolation. For lower channel counts, the SC-206x accessories
provide eight optically isolated inputs or outputs with 400 V
rms
of
channel-to-channel isolation. Another option is SSR modules, which
provide 4000 V
rms
of channel-to-channel isolation in 8, 16, 24, or
32-channel backplanes. For electromechanical relay outputs, the
Family
NI 6527
NI 6507
NI 6508
Product
PCI-6527
PXI-6527
PCI-DIO-96
PXI-6508
PC-DIO-96
DAQPad-6507/6508
PCI-6503
DAQCard-DIO-24
PC-DIO-24
Bus
PCI
PXI
PCI
PXI
ISA
USB
PCI
PCMCIA
ISA
Digital I/O Lines
24 inputs and
24 outputs
96
Logic Level
28 V input and
60 V output
5 V TTL/CMOS
For complete and up-to-date information about accessories, visit
ni.com/catalog
Table 3. Digital I/O Signal Conditioning Accessories.
Isolation
✓
Handshaking I/O
1
–
Change Notification
✓
8255 Chipset
–
Pattern Matching
–
Page
377
–
✓
–
✓
✓
379
NI 6503
24
5 V TTL/CMOS
–
✓
–
✓
✓
379
1
Handshaking
supplied by the 8255; only one handshaking mode is available. See page 376 for details.
Table 1. Digital I/O Products Specifications Summary (See page 385 for detailed specifications.)
374
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