
Appendix D
Hardware Considerations
©
National Instruments Corporation
D-5
Power-On State
When the computer is first turned on, all lines are configured for input and
in the high-impedance state. By default, the data and control lines in the
653
X
device are pulled down, even if the CPULL and DPULL are
disconnected. You can select the biasing of control and data signals using
the CPULL and DPULL lines:
•
CPULL line—For control lines, it is a user-configurable 2.2 k
Ω
internal resistor. You can connect the line to +5 VDC (
pull up
) or
connect the line to ground (
pull down
).
•
DPULL line—For data lines, it is a user-configurable 100 k
Ω
internal
resistor. You can connect the line to +5 VDC (
pull up
) or connect the
line to ground (
pull down
).
Caution
Do
not
connect CPULL, DPULL, or any other line directly to an external power
supply while the 653
X
device is powered off. Doing this may prevent your computer from
booting.
For example, if you are using active-low handshaking signals, you can
connect the CPULL line to +5 V to place the handshaking lines in the high,
inactive state at power up.
Power Connections
The +5 V pin on the I/O connector supplies power from the computer
power supply through a self-resetting fuse. The fuse resets automatically
within a few seconds after removal of an overcurrent condition. The power
pin is referenced to the GND pins and can supply power to external digital
circuitry. The power ratings for the +5 V pin for the various 653
X
devices
are shown in Table D-1.
Table D-1.
653
X
Power Ratings
Device
Power Rating
PCI-DIO-32HS
+4.65 to +5.25 VDC at 1 A
PXI-6533
AT-DIO-32HS
DAQCard-6533 for PCMCIA
+4.65 to +5.25 VDC at 250 mA