User manual

Chapter 4 NI-DAQ Double Buffering
© National Instruments Corporation 4-9 NI-DAQ User Manual for PC Compatibles
Figure 4-6. Double-Buffered Output with an Overwrite
In Figure 4-6b, NI-DAQ has started to copy data from the transfer buffer
to the first half of the circular buffer. However, NI-DAQ is unable to copy
all of the data before the output device begins retrieving data from the first
half (Figure 4-6c). Consequently, device data output might be corrupted; it
might contain both old and new data points. Future transfers will execute
normally as long as neither of these problem conditions occur again.
Double-Buffered Functions
Double-buffered functions exist for analog input (
DAQ
), analog output
(
WFM
), digital input/output (
DIG
), and general-purpose counter (
GPCTR
)
operations. This section explains what each of the functions do and the
order in which you should call them.
Outgoing
Device Data
Circular Buffer
Transfer Buffer
Empty
Buffer
Data Ready
for Output
Successfully
Output Data
Corrupted
Output
a. b.
c.
Overwrite Error