User manual

Chapter 3 Software Overview
NI-DAQ User Manual for PC Compatibles 3-50 ni.com
Note
NI 4451 for PCI and NI 4551 for PCI devices use signed, 18-bit binary data
left-justified in a 32-bit word. Their output voltage range is ±10 V.
Minimum Update Intervals
The rate at which a device can output analog data is limited by the
performance of the host computer. For waveform generation, the limitation
is in terms of minimum update intervals. The update interval is the period
of time between outputting new voltages. Therefore, the minimum update
interval specifies the smallest possible time delay between outputting new
data points. In other words, the minimum update interval specifies the
fastest rate at which a device can output data. Refer to Chapter 4, NI-DAQ
Double Buffering, for more information on the minimum update intervals.
Counter Usage
NI 4451 for PCI and NI 4551 for PCI devices use the same counter for both
waveform generation and analog input data acquisition. See
WFM_Set_Clock
in the NI-DAQ Function Reference Online Help file for
an explanation of the restrictions this causes. This counter is separate from
the general-purpose counters.
The MIO, 671X, 622X, and E Series devices use dedicated counters from
the DAQ-STC chip for waveform-generation control and timing.
On the Lab and 1200 devices and analog output devices, counter A2
produces the total update interval for waveform generation. However,
if the total update interval is greater than 65,535 µs, counter B0 generates
the clock for a slower timebase, which counter A2 uses for the total
update interval. The
ICTR_Setup
and
ICTR_Reset
functions cannot
then use counter B0 for the duration of the waveform generation
AT -AO - 6 /1 0 Negative of
the reference
voltage
(–10 V in
default case)
Reference
voltage
(+10 V in
default case)
— —
Lab and 1200 devices
with analog output
–5V +5 V — —
Table 3-5. Output Voltages with Bipolar Output Polarity (Continued)
Device
Value in Waveform Buffer
–2,048 2,047 –32,768 32,767