Programming instructions

Chapter 20 DSA Devices
© National Instruments Corporation 20-5 DAQ Hardware Overview Guide
DSA devices accept data values in a left-justified 32-bit data format. This
means that the most significant bits of the data value contain the bits that
will be written to the converter. Even though the
WFM functions are declared
to accept pointers to 16-bit data buffers, you should pass the pointers to
32-bit data buffers for the DSA devices.
The DDS clock signal is shared by the input and the output sections of the
device. The ADCs and DACs have separate internal divides of the DDS
clock, so that at the maximum DDS rate the input ADCs run at four times
the sample rate of the DACs. The device does have an independent divide
down circuit for each analog section, so that you can adjust the DDS clock
by powers of two. This circuitry allows you to set the rate for both the
ADCs and DACs to the same scan clock rate. The
WFM_Set_Clock
function automatically makes this adjustment and tries to make a setting
compatible with the analog input clock setting mode. If a data acquisition
operation is already running, the waveform clock is constrained to
frequencies compatible with the data acquisition clock.
You can configure the waveform generation to start when the device
receives a digital trigger. The device can receive the digital trigger from
either the digital I/O connector or the RTSIbus. Notice that the first update
after the trigger does not appear at the outputs until 30 to 40 updates have
been generated. This behavior is a feature of the digital anti-imaging filter
in the converter and cannot be disabled.
PCI-445 X and NI 455 X Digital I/O
This section contains information regarding the port configuration for the
445X and 455X, which support DIO lines.
PCI-445 X Digital I/O
The PCI-4451 and PCI-4452 contain one 8-bit digital I/O port supplied by
the DAQ-STC chip. This port is referred to as port 0 by the Digital I/O
functions.
You can configure the entire digital port as either an input or an output port,
or you can configure individual lines for either input or output.The port has
read-back capability. This port operates in nonlatched mode only.
The PCI-4453 and PCI-4454 do not support digital I/O.