Functional Details; Theory Of Operation - Analog Input Acquisition Modes; Software Paced Mode; Continuous Scan Mode - Measurement Computing USB-1616FS User Manual

Functional Details

Theory of operation - analog input acquisition modes

The USB-1616FS 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 any one
channel.
The maximum throughput sample rate in software paced mode is about 250 S/s, but may vary depending on
your system.

Continuous scan mode

You can acquire data from up to 16 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-
1616FS until you stop the scan. The FIFO buffer is serviced in blocks as the data is transferred from the
USB-1616FS FIFO buffer to the memory buffer on your computer.
You can acquire data with the USB-1616FS from one channel at 50 kS/s and up to 16 channels at 9.5 kS/s
each. Table 4-1 on page 4-2 lists the throughput rates for 1 to 16 channels. 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-1616FS using the full capacity of its 32K sample
FIFO. The acquired data is then read from the FIFO and transferred to a user memory buffer on the
computer. You can initiate a single acquisition sequence for any number of input 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. The maximum rate for each
channel is 50 kS/s. The maximum rate that you can acquire data using burst scan mode is 50 kS/s per
channel for one, two, or four channels, and 12.5 kS/s per channel for 16 channels.
3-1
Chapter 3