Buffer and half buffer sizes

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Hi

I have a question regarding buffer size. I am working with a PCI-6025E board and NIDAQ functions to control it (v 6.9.1).

For E Series devices, SCAN_Start requires the total number of scans be at least 2. Does this follow for continuous reading mode too? (i.e., double buffering). Alternatively, what is the minimum number of scans a half buffer should cater?

Peter

[Geneva L.]

Peter,

In the NI-DAQ Help file for SCAN_Start, you can see that buffer must have a length equal to or greater than count. However, this may not be what you want to do. If your purpose is to read 2 channels once or 1 channel twice, then you should just use a single buffered scan.

Regards,
Geneva L.
Applications Engineer
National Instruments
http://www.ni.com/support

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Hi Geneva L

Thanks for your reply.

I wish to read 2 channels every time an external trigger is received. The scanning is controlled externally DAQ_Config( , 0, 2 ) and am using Select_Signal( , ND_IN_SCAN_START, ND_PFI_0, ND_LOW_TO_HIGH ). Every time a scan is complete, I wish to perform some other operations, then issue a command to arm our equipment. Only on SCAN_Start command is issued to initiate the acquisition process.

So if I am double buffering, the half buffer size would contain 2 samples (1 scan), and the count in SCAN_Start would be 4 (for two scans), with buffer size 4. However I found DAQ_DB_Transfer returning with overwrite errors, which I should not see; on the other hand, I may have misunderstood.

Peter