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Chapter 3
Functional Details
Analog input acquisition modes
The USB-1608FS can acquire analog input data in three modes – software paced, hardware paced, and
BURSTIO.
Software paced
The USB-1608FS acquires data one analog sample at a time using software-paced mode. You initiate the A/D
conversion by calling a software command. The analog value is converted to digital and returned to the
computer. You can repeat this procedure until you have the total number of samples that you want.
The USB-1608FS can attain throughput rates up to 500 S/s using a software loop. This rate is system-
dependent.
Hardware paced
The USB-1608FS 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 USB-1608FS
until you stop the scan. Data is transferred from the USB-1608FS FIFO buffer to the memory buffer on your
computer.
The A/D converter is paced by either an internal or external clock source.
The maximum sample rate is an aggregate rate. 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, the USB-1608FS can
acquire data 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 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 can acquire data at higher rates using the full capacity of the
32 kilosample FIFO. The acquired data is then 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, two, four, or
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 is 200 kS/s. The maximum sample
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 sample rate that you can acquire data using BURSTIO is 50 kS/s each for one, two, or four
channels, and 25 kS/s each for eight channels.
