National Instruments 653X Manuale Utente

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 
653X device.

For unstrobed I/O, the direction of each of the 32 data lines is individually 
configurable. You can configure each data line to one of the following:

•

Input

•

Standard output

•

Wired-OR output

A standard driver drives its output pin to approximately 0 V for logic low, 
or +5 V for logic 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.

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 +5 V pin. This provides 100 k

Ω pull-up resistors on all data lines. 

For more information about CPULL and DPULL, see the 

section in Appendix D,