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Chapter 3
Functional Details
Theory of operation - analog input acquisition modes
The UMDAS 0802DA 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, converted to digital values, and written to an on-board FIFO buffer until you stop the scan. The FIFO
buffer is serviced in blocks as the data is transferred from the UMDAS 0802DA 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 UMDAS 0802DA has the following external components, as shown in Figure 3-1.
! USB connector
! LED
! Screw terminal banks (2)
USB
connector
Screw terminal
Pins 21 to 40
Screw terminal
Pins 1 to 20
LED
Figure 3-1. UMDAS 0802DA external components
3-1