Measurement Computing USB-1608GX-2AO-OEM - Manual (Page 9)

9
Chapter 3
Functional Details
Analog input modes
The USB-1608GX-2AO-OEM can acquire analog input data in two basic modes – software paced and hardware
paced.
Software paced
You can acquire one analog sample at a time in software paced mode. You initiate the A/D conversion with a
software command. The analog value is converted to digital data and returned to the computer. Repeat this
procedure until you have the total number of samples that you want.
The sample rate in software paced mode is system-dependent and can range from 33 S/s to 4000 S/s.
Hardware paced
You can acquire data from up to 16 channels in hardware paced mode. The analog data is continuously
acquired, converted to digital values, and written into the FIFO buffer on the device until you stop the scan. The
FIFO buffer is serviced in blocks as the data is transferred from the FIFO buffer to the computer memory
buffer. You start a continuous scan with either a software command or with an external hardware trigger event.
The maximum sampling rate in hardware paced mode from one to 16 channels is 500 kS/s aggregate.
Burst mode
When using the onboard pacer, you can enable burst mode for more precise timing between samples. When
burst mode is enabled, each successive channel in a scan is sampled at the maximum A/D rate. This ensures that
samples from each channel are taken as close as possible to the same absolute point in time. When burst mode
is disabled, data is sampled at evenly spaced intervals, allowing maximum settling time and best amplitude
accuracy. Multi-channel scanning with burst mode enabled and disabled is shown in Figure 2.
Figure 2. Multi-channel scan with burst mode enabled and disabled
The burst mode sample period is 2 µs.
You can trigger the acquisition with the external trigger, and control the clock period with the internal or
external A/D pacer clock. Pacing from the external clock always operates with burst mode enabled.