Measurement Computing USB-2020 - Manual (Page 11)

Chapter 3
Functional Details
Analog input acquisition modes
The USB-2020 can acquire analog input data in three different modes – software paced, continuous scan
(hardware paced), and BURSTIO.
Software paced
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 repeat
this procedure until you have the total number of samples that you want from one channel.
The typical throughput sample rate in software paced mode is 4 kS/s (system-dependent).
Continuous scan (hardware paced)
Continuous scan mode enables data to be directly transferred to the host computer during acquisition. The
maximum rate in continuous scan mode is 8 MS/s for all acquired data (one channel or two channels). The
maximum rate achieved depends on the host computer..
BURSTIO
When using BURSTIO, the USB-2020 can acquire data at the maximum rate of 20 MS/s per channel to the
internal memory buffer (up to 64 megasamples) 1 . The acquired data is read from the FIFO and transferred to a
user buffer in the computer. You can initiate a single acquisition sequence of one to two channels with either a
software command or an external hardware trigger event.
When BURSTIO is enabled, scans are limited to the depth of the onboard memory, as the data is acquired at a
rate faster than it can be transferred to the computer. Time must be allowed between scans for the acquisition
and
the transfer of the data.
1 In some situations, the available memory is restricted below 64 megasamples. Refer to Buffer
size limitations on Windows systems
on page 15 for more information.
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