National Instruments 321645c-01 用户手册
Chapter 2
Function Reference — GPCTR_Read_Buffer
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National Instruments Corporation
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NI-DAQ FRM for PC Compatibles
GPCTR_Read_Buffer
Format
status = GPCTR_Read_Buffer (deviceNumber, gpctrNum, readMode, numPts, readOffSet,
timeOut, buffer)
Purpose
Returns the data from a asynchronous counter input operation. The read mode and offset
combined allow you to specify the location from which to read the data for 6602 and 455X
devices only.
combined allow you to specify the location from which to read the data for 6602 and 455X
devices only.
Parameters
Input
Parameter Discussion
gpctrNum indicates which counter to program. Legal values for this parameter are shown in
Table 2-19.
Table 2-19.
The type of read operation specified in readMode is used in conjunction with the readOffSet
to compute the reading mark. Basically, read mark = reading point (specified by readMode)
+ readOffSet. The readMode can have the following legal values:
to compute the reading mark. Basically, read mark = reading point (specified by readMode)
+ readOffSet. The readMode can have the following legal values:
•
ND_READ_MARK
—The reading point is placed at the location of the current read mark.
•
ND_BUFFER_START
—The reading point is placed at the start of the buffer.
•
ND_WRITE_MARK
—The reading point is placed at a position in the buffer that has the
latest data.
Name
Type
Description
deviceNumber
i16
assigned by configuration utility
gpctrNum
u32
number of the counter to use
readMode
u32
the parameter to set the reading point in the buffer
numPts
u32
the number of points to read
readOffSet
i32
the offset from the reading point
timeOut
u32
time for which this function will wait before
returning
returning
buffer
u32
destination buffer for the data