Chapter 3 Functional Details; Theory Of Operation - Analog Input Acquisition Modes; Software Paced Mode; Continuous Scan Mode - Measurement Computing USB-1408FS User Manual

Functional Details

Theory of operation - analog input acquisition modes

The USB-1408FS can acquire analog input data in two different modes – software paced and continuous scan.

Software paced mode

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 can
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 system-dependent.

Continuous scan mode

In continuous scan mode, you can acquire data from up to eight channels. The analog data is continuously
acquired and converted to digital values until you stop the scan. Data is transferred in blocks of 31 samples from
the USB-1408FS to the memory buffer on your computer.
The maximum continuous scan rate of 48 kS/s is an aggregate rate. The total acquisition rate for all channels
cannot exceed 48 kS/s. You can acquire data from one channel at 48 kS/s, two channels at 24 kS/s, and four
channels at 12 kS/s. You can start a continuous scan with either a software command or with an external
hardware trigger event.

External components

The USB-1408FS has the following external components, as shown in Figure 3.

USB connector

LED

Screw terminal banks (2)
Screw terminal
Pins 21 to 40
LED
Figure 3. USB-1408FS external components
14
Screw terminal
Pins 1 to 20
USB
connector / cable
Chapter 3