Controlling Line Polarities; Creating A Program - National Instruments 653 Series User Manual

Creating a Program

© National Instruments Corporation
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 653X 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 653X 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 kΩ 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
Hardware Considerations.
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.
Power-On State
2-23
Chapter 2 Using Your NI 653X
section of Appendix D,
NI 653X User Manual