Measurement-computing WaveBook rev.3.0 Instrukcja Użytkownika Pobierz pdf (Strona 151)

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

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)

11—

22—

33—

443

55—

66—

77—

886

12—

243

36—

486

13—

26—

39—

4129

515—

618—

721—

82418

143

286

3129

41612

…………

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

1 2 ... 146 147 148 149 150 151 152 153 154 155 156 ... 235 236

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