National Instruments 653X - Manual (Page 30)

Chapter 2 Using Your 653X
653X User Manual 2-12 ni.com
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.
Controlling Line Polarities
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
Power-On State section in Appendix D,
Hardware Considerations .
Creating a Program
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.