National Instruments 653X Manuale Utente

Controlling the startup sequence does not apply to buffered (block) 
operations. In a buffered operation, the NI-DAQ C interface configures and 
enables the 653X device at the same time, when you start the actual data 
transfer. For buffered operations, control the line polarities as a start-up 
method.

If you cannot control the initialization order of the 653X device and 
peripheral device, you can ensure an optimum startup if you select the 
polarities of the ACK and REQ lines so that the power-up, undriven states 
of the control lines are the inactive states.

By default, the power-up, undriven control-line state of the REQ and ACK 
lines is low. If you want to change state to high, use one of the three 
following methods:

•

Use the CPULL bias-selection line and connect the CPULL pin on the 
I/O connector to the +5 V pin. This provides 2.2 k

Ω pull-up resistors 

on all control lines.

•

Choose a mode with active-high REQ and ACK signals.

•

Use your own pull-up resistors.

For information about using the CPULL line to control the pull-up and 
pull-down resistors, see the 

 section in Appendix D, 

Using the following flowcharts as a guide, create a program to 
perform handshaking I/O. Figures 2-4 and 2-5 display flowcharts for 
C programming using NI-DAQ, while Figures 2-6 and 2-7 show a 
LabVIEW programming flowcharts.

The boxes represent function names for the appropriate software, and the 
diamonds represent decision points.