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)

LED

Screw terminal

Pins 1 to 20

Screw terminal

Pins 21 to 40

USB

connector

Figure 3-1. UMDAS 0802DA external components

3-1