Measurement Computing USB-1408FS - Manual (Page 9)

9
Chapter 3
Functional Details
Analog input acquisition modes
The USB-1408FS can acquire analog input data in either software-paced or hardware-paced mode.
Software paced
The USB-1408FS 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-1408FS can attain throughput rates up to 250 S/s using a software loop. This rate is system-
dependent.
Hardware paced
The USB-1408FS can acquire data from up to eight channels in hardware-paced mode. The analog data is
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 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 48 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 48
2 24
3 16
4 12
5 9.60
6 8
7 6.85
8 6
You start a hardware-paced scan with a software command. Optionally, hardware-paced scans can be delayed
by an external hardware trigger event.