Справочник Пользователя для National Instruments 321645c-01
Chapter 2
Function Reference — DIG_DB_HalfReady
NI-DAQ FRM for PC Compatibles
2-160
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National Instruments Corporation
DIG_DB_HalfReady
Format
status = DIG_DB_HalfReady (deviceNumber, group, halfReady)
Purpose
Checks whether the next half buffer of data is available during a double-buffered digital block
operation. You can use
operation. You can use
DIG_DB_HalfReady
to avoid the waiting period that can occur
because
DIG_DB_Transfer
waits until NI-DAQ can transfer the data before returning.
Parameters
Input
Output
Parameter Discussion
group is the group to be configured.
Range:
1 or 2.
halfReady indicates whether the next half buffer of data is available. When halfReady equals
one, you can use
one, you can use
DIG_DB_Transfer
to read or write the data immediately. When halfReady
equals zero, the data is not yet available.
Note
C Programmers—halfReady is a pass-by-reference parameter.
Using This Function
Double-buffered digital block functions cyclically input or output digital data to or from a
buffer. The buffer is divided into two equal halves so that NI-DAQ can save or write data
from one half while block operations use the other half. For input, this mechanism makes it
necessary to alternately save both halves of the buffer so that NI-DAQ does not overwrite
data in the buffer before saving the data. For output, the mechanism makes it necessary to
alternately write to both halves of the buffer so that NI-DAQ does not output old data. Use
buffer. The buffer is divided into two equal halves so that NI-DAQ can save or write data
from one half while block operations use the other half. For input, this mechanism makes it
necessary to alternately save both halves of the buffer so that NI-DAQ does not overwrite
data in the buffer before saving the data. For output, the mechanism makes it necessary to
alternately write to both halves of the buffer so that NI-DAQ does not output old data. Use
DIG_DB_Transfer
to save or write the data NI-DAQ is inputting or outputting the data. This
Name
Type
Description
deviceNumber
i16
assigned by configuration utility
group
i16
group
Name
Type
Description
halfReady
i16
whether the next half of data is available