How does data enter/leave the ni4351(pci) buffer?

Question

I have recently begun using an ni4351(pci) for data acquisition. I'm using VC++ on a Win95 system. I've been digging through the documentation for the ni435x instrument driver, but I can't locate an anwer to the following question: How does the buffer for the analog input scans work?
It's stated in the instrument driver help that if the function to set the number of scans is not called, then acquisition will be continuous. My questions all revolve round the concept of continuous acquisition. I believe that I understand what's going on until i look at the fcns that read/check the acquisition.
What is the purpose of the timeout variable? I undertand its general purpose, but it seems (to me) that we must pass a ti
meout variable to functions that should never time out (e.g. check and read which only returns data that has already been collected).
How is data written into the buffer? is it sequentially added? (e.g. the first data point is buffer[0] and the last would be buffer[999] in a 1k element buffer?) or maybe the most recent acquisition is stored in buffer[0] and older data gets bumped back?
What happens to the data after a read (or check and read) has been performed? is the buffer cleared? does the data keep getting entered sequentially as if nothing has happened?
I apologize if this is in a document somewhere on your site. Thanks in advance for your help.

Answer 1

Data is written into the buffer sequentially. The buffer that the data is written to is a circular buffer. When the values are read into your program as an array, the first point that was acquired will be first in your array. The following tutorial explains what going on in hardware during a continuous acquisition:
http://zone.ni.com/devzone/conceptd.nsf/webmain/F2DDCBAD754C687C86256802007B8514?opendocument
I hope this answers your questions, feel free to post again if it doesn�t.
Best Regards,
Doug K
Application Engineering
National Instruments