Chapter 2
Using Your NI 653X
©
National Instruments Corporation
2-23
Controlling the startup sequence does not apply to buffered (block)
operations. In a buffered operation, the NI-DAQ C interface configures and
enables the NI 653
X
at the same time, when you start the actual data
transfer. For buffered operations, control the line polarities as a start-up
method.
Controlling Line Polarities
If you cannot control the initialization order of the NI 653
X
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, refer to the
section of Appendix D,
Creating a Program
Using the following flowcharts as a guide, create a program to
perform handshaking I/O. Figures 2-11 and 2-12 display flowcharts for
C programming using NI-DAQ, and Figures 2-13 and 2-14 show
LabVIEW programming flowcharts.
The boxes represent function names for the appropriate software, and the
diamonds represent decision points.
