Functional Details; Theory Of Operation - Analog Input Acquisition Modes; Software Paced Mode; Continuous Scan Mode - Measurement Computing USB-1608FS User Manual

Functional Details

Theory of operation - analog input acquisition modes

The USB-1608FS can acquire analog input data in three basic modes – software paced, continuous scan, and
burst scan.

Software paced mode

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

Continuous scan mode

You can acquire data from up to eight channels simultaneously in continuous scan mode. The analog data is
continuously acquired, converted to digital values, and written to an on-board FIFO buffer on the USB-1608FS
until you stop the scan. The FIFO buffer is serviced in blocks as the data is transferred from the USB-1608FS
FIFO buffer to the memory buffer on your computer.
The maximum sampling rate is an aggregate rate, where the total sample rate for all channels is 100 kS/s
divided by the number of channels, with a maximum rate of 50 kS/s for any channel. Using this equation, you
can acquire data with the USB-1608FS from one channel at 50 kS/s, two channels at 50 kS/s each, four
channels at 25 kS/s each, and so on, up to eight channels at 12.5 kS/s each. 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 with the USB-1608FS using the full capacity of its 32 K sample FIFO.
The acquired data is then read from the FIFO and transferred to a user buffer in your computer. You can initiate
a single acquisition sequence of one, two, four, or eight channels by either a software command or an external
hardware trigger.
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, where the total acquisition rate
for all channels is 200 kS/s divided by the number of channels, with a maximum rate of 50 kS/s for any channel.
The maximum rate that you can acquire data using burst scan mode is 50 kS/s each for one, two, or four
channels, and 25 kS/s each for eight channels.
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Chapter 3