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Chapter 3

Functional Details

Theory of operation - analog input acquisition modes

The 18200-00 can acquire analog input data in three different modes – software paced, continuous scan, and burst scan.

Software paced mode

In software paced mode, you can acquire one analog sample at a time. You initiate the A/D conversion by calling a software command. The analog value is converted to digital and returned to the computer. You can repeat this procedure until you have the total number of samples that you want from one channel.

Software pacing is limited by the 20 mS round-trip requirement of a USB interrupt-type endpoint operation.

The maximum throughput sample rate in software paced mode is 50 S/s.

Continuous scan mode

In continuous scan mode, you can acquire data from up to eight channels. The analog data is continuously acquired, converted to digital values, and written to an on-board FIFO buffer until you stop the scan. The FIFO buffer is serviced in blocks as the data is transferred from the 18200-00 to the memory buffer on your computer.

The maximum continuous scan rate of 1.2 kS/s is an aggregate rate. The total acquisition rate for all channels cannot exceed 1.2 kS/s. You can acquire data from one channel at 1.2 kS/s, two channels at 600 S/s and four channels at 300 S/s. You can start a continuous scan with either a software command or with an external hardware trigger event.

Burst scan mode

In burst scan mode, you can acquire data using the full capacity of the 18200-00 4 k sample FIFO. You can initiate a single acquisition sequence of up to 4096 samples channels by either a software command or an external hardware trigger. The captured data is then read from the FIFO and transferred to a user buffer in the host PC.

Burst scans are limited to the depth of the on-board memory, as the data is acquired at a rate faster than it can be transferred to the computer. The maximum sampling rate is an aggregate rate. The maximum rates that you can acquire data using burst scan mode is 8 kS/s divided by the number of channels in the scan.

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