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4. Digital Input (DI)
This chapter introduces the digital input signal acquisition on USB-3200 series data acquisition
devices
. DI is the abbreviation of Digital Input here. Figure 4.1 is a schematic diagram of the
digital input circuit.
Figure 4.1 digital input circuit Figure
4.1.
Signal acquisition mode
When the USB-3200 series data acquisition
device
performs DI acquisition, it supports
continuous acquisition mode or limited number acquisition mode. The sampling rates of both
modes are hardware-timed. The limited number acquisition mode is called OneShot mode.
Hardware timing
Hardware timing refers to the sampling rate of the sample acquired by DI. It is controlled by the
hardware digital signal (DI sampling clock). This signal can be generated internally or externally.
For details on using an externally supplied sampling clock, refer to the "Synchronization System"
chapter.
Continuous acquisition mode
The continuous acquisition mode refers to continuous and uninterrupted data acquisition at a set
sampling speed.
In the continuous acquisition mode, after the DI acquisition triggers, the acquisition
device
collects the signal at a fixed sampling speed, buffers it in the FIFO, and continuously uploads the
data in the FIFO to the computer memory buffer. The user program only needs to continuously
process the data in memory to achieve continuous uninterrupted data collection.
If the user program could not process the data fast enough, the data will gradually fill up the 2M
points of storage space in the computer's memory buffer. After filling it up, the new data cannot be
written into memory buffer correctly, resulting in data discontinuity.