Chapter 3
Signal Connections
PCI-DIO-96/PXI-6508/PCI-6503 User Manual
3-10
ni.com
Power Connections
Pin 49 and, on the PCI-DIO-96 and PXI-6508, pin 99 of the I/O connector
5 V from the computer power supply via a self-resetting fuse. The
fuse resets automatically within a few seconds after the overcurrent
condition is removed. These pins are referenced to GND and can be used
to power external digital circuitry.
Power rating.................................... 1 A at +4.65 to +5.25 V
Caution
Never connect the +5 V power pins directly to ground or to any other voltage
source on your DIO board or to any other device. Doing so can damage your DIO board
and the computer. National Instruments is
not
liable for damage resulting from such a
connection.
Digital I/O Power-up State Selection
The PCI-DIO-96, PXI-6508, and PCI-6503 contain bias resistors that
control the state of the digital I/O lines at power up. At power up, each
digital I/O line is configured as an input, pulled either high or low by a
100 k
Ω
bias resistor.
On the PCI-DIO-96, all of the 100 k
Ω
bias resistors pull up. Therefore, the
default power-up state of each line on the PCI-DIO-96 is high.
On the PXI-6508 and PCI-6503, you can select the direction of the 100 k
Ω
bias resistors. Set jumper W1 to high to configure the resistors as pull-up
resistors. Set jumper W1 to low to configure the resistors as pull-down
resistors.
You can change individual lines from pulled up to pulled down—or, on the
PXI-6508 and PCI-6503, from pulled down to pulled up—by adding your
own external resistors. This section describes the procedure.
High DIO Power-up State
If you select the pulled-high mode, each DIO line is pulled to V
cc
(approxi5 VDC) with a 100 k
Ω
resistor. To pull a specific line low,
connect between that line and ground a pull-down resistor (R
L
) whose
value will give you a maximum of 0.4 VDC. The DIO lines provide a
maximum of 2.5 mA at 3.7 V in the high state. Using the largest possible
resistor ensures that you do not use more current than necessary to perform
the pull-down task.