
Appendix D Hardware Considerations
© National Instruments Corporation D-5 653X User Manual
Power-On StateWhen 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 
653Xdevice 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 2.2kΩ 
internal resistor. You can connect the line to +5VDC (pull up) or 
connect the line to ground (pull down).
•DPULL line—For data lines, it is a user-configurable 100kΩ internal 
resistor. You can connect the line to +5VDC (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 653Xdevice 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 ConnectionsThe +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 +5V pin for the various 653Xdevices 
are shown in TableD-1.
Table D-1.   653X Power Ratings
Device Power Rating
PCI-DIO-32HS
+4.65 to +5.25VDC at 1 A
PXI-6533
AT-DIO-32HS
DAQCard-6533 for PCMCIA +4.65 to +5.25 VDC at 250 mA