National Instruments NI 6509 Change Detection, Change Detection Example

Change Detection

You can program the NI 6509 to send an interrupt when a change occurs on

any input line.

The NI 6509 can monitor changes on selected input lines or on all input

lines. It can monitor for rising edges (0 to 1), falling edges (1 to 0), or both.

When an input change occurs, the NI 6509 generates an interrupt, and the

NI-DAQ driver then notifies the software.

Note Excessive change detections can affect system performance. Use digital filtering to

minimize the effects of noisy input lines.

The NI 6509 sends a change detection when any one of the changes occurs,

but it does not report which line changed or if the line was rising or falling.

After a change, you can read the input lines to determine the current line

states. The maximum rate of change detection is determined by the

software response time, which varies from system to system.

An overflow bit indicates that an additional rising or falling edge has been

detected before the software could process the previous change.

Refer to the software documentation for information about how to set up

and implement the change detection.

Change Detection Example

Table 2 shows a change detection example for six bits of one port.

Table 2. Change Detection Example

Bit

76543210

Changes to detect — —

Enable rising-edge

detection

yes yes yes yes no no yes no

Enable falling-edge

detection

yes yes yes yes no no no yes