9
Chapter 3
Functional Details
Analog input acquisition modes
The USB-1208FS-Plus can acquire analog input data in either software paced or hardware paced mode.
Software paced
The USB-1208FS-Plus 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 maximum sample rate in software-paced mode is system-dependent.
Hardware paced
The USB-1208FS-Plus can acquire data from up to eight channels using hardware-paced mode. The analog data
is acquired and converted to digital values until you stop the scan. Data is transferred in blocks of 32 samples
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 sample rate is an aggregate rate. The total sample rate for all channels cannot exceed 50 kS/s.
The following table lists the sample rate when scanning from one to eight channels.
Maximum per channel sample rate
# channels
scanned
Sample rate
(kS/s)
1
50
2
25
3
16.70
4
12.50
5
10
6
8.30
7
7.14
8
6.25
You can start a hardware-paced scan with a software command. Optionally, hardware-paced scans can be
delayed by an external hardware trigger event.