Measurement Computing USB-1616FS - Manual (Page 12)

12
Chapter 3
Functional Details
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
With software paced mode you 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 data and returned to the computer. 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 about 250 S/s, but may vary depending on
your system. You may receive OVERRUN errors at higher rates on some platforms. Using the burst scan mode
(BURSTIO) should resolve these problems.
Continuous scan
With hardware paced mode you acquire data from up to 16 channels simultaneously. 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 device 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.
The throughput rates for 1 to 16 channels are listed in the Specifications section on page 23. You can start a
continuous scan with either a software command or with an external hardware trigger event.
Burst scan
With burst scan mode (BURSTIO), you can acquire data using the full capacity of its 32 k sample FIFO on the
device. 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.