Chapter 2 Using Your 653X
653X User Manual 2-2 ni.com
Controlling and Monitoring Static Digital Lines—Unstrobed I/O
This section explains how to control and monitor static digital lines through
software-timed reads and writes to and from the digital lines of your
653Xdevice.

Configuring Digital Lines

For unstrobed I/O, the direction of each of the 32data lines is individually
configurable. You can configure each data line to one of the following:
•Input
•Standard output
•Wired-OR output

Standard Output

A standard driver drives its output pin to approximately 0 V for logic low,
or +5V for lo gic high. Advantages include:
•It does not require pull-up resistors.
•It is independent of the state of the DPULL line.
•It has high current drive for both its logic high and logic low states.
•It can drive high-speed transitions in both the high-to-low and
low-to-high directions.

Wired-OR Output

A wired-OR output driver drives its output pin to 0 V for logic low. For
logic high, the output driver assumes a high-impedance state and does not
drive a voltage. This is called tri-state. To pull the pin to +5 V for logic
high, a pull-up resistor is required.
To provide a pull-up resistor, connect the DPULL pin on the I/O connector
to the +5V pi n. This provides 100kΩ pull-up resistors on all data lines.
Formore information about CPULL and DPULL, see the Power-On Sta te
section in AppendixD, Hardware Considerations.