Measurement Computing USB-1608FS-Plus - Manual (Page 9)

9
Chapter 3
Functional Details
Analog input modes
The USB-1608FS-Plus can acquire analog input data in three modes – software paced, hardware paced, and
BURSTIO.
Software paced
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.
The USB-1608FS-Plus can attain throughput rates up to 500 S/s using a software loop. This rate is system-
dependent.
Hardware paced
The USB-1608FS-Plus can acquire data from up to eight channels simultaneously in hardware-paced mode. The
analog data is acquired, converted to digital values, and written to an onboard FIFO buffer on the device until
you stop the scan. Data is transferred in blocks from the device to the memory buffer on your computer.
The A/D converter is paced by either an internal or external clock source.
The maximum sampling rate is an aggregate rate. The total sample rate using hardware-paced mode is 400 kS/s
divided by the number of channels, with a maximum rate of 100 kS/s for any channel. You can acquire data
from one to four channels at 100 kS/s each, six channels at 66.7 kS/s each, and so on, up to eight channels at
50 kS/s each. You can start a hardware-paced scan with a software command. Optionally, hardware-paced scans
can be delayed by an external hardware trigger event.
BURSTIO
When using BURSTIO, the USB-1608FS-Plus can acquire data at a higher rate using the full capacity of the
32 kilosample FIFO. The acquired data is read from the FIFO and transferred to a user buffer in the computer
after the acquisition is complete. You can initiate a single acquisition sequence of one to eight channels with a
software command. Optionally, BURSTIO scans can be delayed by an external hardware trigger event.
When BURSTIO is enabled, the number of samples acquired in a scan is limited to the depth of the onboard
memory. The maximum sample rate in BURSTIO mode is an aggregate rate of 800 kS/s. The maximum per
channel sample rate is 100 kS/s for any or all channels.