You can configure the USB-6423 to detect changes on all 16 digital input lines (P0).

The following figure shows a block diagram of the digital I/O change detection circuitry.

Figure 50. Digital Input Change Detection


You can enable the digital I/O change detection circuitry to detect rising edges, falling edges, or either edge individually on each digital I/O line. The USB-6423 synchronizes each digital input signal to the 100 MHz Timebase, and then sends the signal to the change detectors. The circuitry ORs the output of all enabled change detectors from every digital input signal. The result of this OR is the Change Detection Event signal.

Change detection performs bus correlation by considering all changes within a 50 ns window one change detection event, which keeps signals on the same bus synchronized in samples and prevents overruns.

The Change Detection Event signal can do the following:

  • Drive any DIO <0..15> signal
  • Drive the DO Sample Clock or DI Sample Clock
  • Generate an interrupt

The Change Detection Event signal can also be used to detect changes on digital output events.

DI Change Detection Applications

The digital I/O change detection circuitry can interrupt a user program when one of several digital I/O signals changes state.

You can also use the output of the digital I/O change detection circuitry to trigger a digital input or counter acquisition on the logical OR of several digital signals. By routing the Change Detection Event signal to a counter, you can also capture the relative time between bus changes.

You can also use the Change Detection Event signal to trigger digital output or counter generations.