Data transfer, Time-outs, Buffer size and type – Measurement Computing WaveBook rev.3.0 User Manual
Page 151: Ansfer…… 8-17, Pe…… 8-17
WaveBook User’s Manual.
6-24-99
Theory of Operation 8-17
Data Transfer
Once an acquisition starts, WaveBook will begin acquiring samples either immediately (if pre-trigger is
enabled) or after the trigger. These samples are initially placed into WaveBook's internal 64K-word first-
in-first-out (FIFO) buffer. The PC must retrieve the samples from the FIFO soon after acquisition starts;
otherwise, the FIFO will become full, samples will be lost, and an error will be indicated. The retrieved
samples are transferred into data buffers in the PC's memory.
Note: The WBK30 Memory Option adds a much larger data buffer to WaveBook; refer to the WBK30
section of chapter 3.
Time-Outs
While the PC is controlling and transferring data from WaveBook, the PC's application program is unable
to execute commands. To keep the program from hanging indefinitely, WaveBook has a timer that will stop
WaveBook operation with an error if the application program has been suspended for more than a specified
number of milliseconds. The time-out interval is set with daqSetTimeout.
Buffer Size and Type
The daqAdcTransferBufData command retrieves the samples from WaveBook into a buffer in the
PC's memory. This command takes many arguments, including those that describe the buffer, as follows:
• Buf refers to the address of the buffer that will hold
the samples.
• ScanCount refers to the size of the buffer in scans.
• Cycle controls the overwriting of old samples.
buf
Scan
1
Scan
2
Scan
3
Scan
scanCount
The buffer must have room for at least scanCount scans. Without data packing, each sample takes one
16-bit integer, and the buffer must be at least (samples-per-scan)*(scanCount words) long (see table).
Scan Length
(samples-per-scan)
Scans per Buffer
(scanCount)
Unpacked Buffer Length
(16-bit words)
Packed Buffer Length
(WaveBook/512 Only)
1
1
—
2
2
—
3
3
—
4
4
3
5
5
—
6
6
—
7
7
—
1
8
8
6
1
2
—
2
4
3
3
6
—
2
4
8
6
1
3
—
2
6
—
3
9
—
4
12
9
5
15
—
6
18
—
7
21
—
3
8
24
18
1
4
3
2
8
6
3
12
9
4
4
16
12
…
…
…
…
1
127
—
2
254
—
3
381
—
4
508
381
5
635
—
6
762
—
7
889
—
127
8
1016
762
1
128
96
2
256
192
3
384
288
128
4
512
384