Справочник Пользователя для National Instruments DAQ 6527

If you anticipate noisy or rapidly changing input lines, use digital filtering 
to reduce the changes to a manageable number; excessive notifications can 
hurt system performance. For example, if you want to limit the rate of 
notifications (and interrupts) to a maximum of one change per line every 
10 ms, set a filter interval of 10 ms.

Table 4-2 shows configuring change notification for five bits of one port. 
This example assumes the following line connections:

•

Bits 7, 6, 5, and 4 are connected to data lines from a four-bit TTL input 
device. The 6527 detects any change in the input data so you can read 
the new data value.

•

Bit 1 is connected to a limit sensor; the 6527 detects rising edges on 
the sensor, which correspond to over-limit conditions.

•

Bit 0 is connected to a switch. Your software can react to any switch 
closure, represented by a falling edge. If the switch closure is noisy, 
you should also enable digital filtering for at least this line.

In this example, the 6527 reports rising and falling edges on bits 7, 6, 5, 
and 4; rising edges only on bit 1; and falling edges only on bit 0. The 6527 
reports no changes for bits 3 and 2. After receiving notification of a change, 
you can read the port to determine the current values of all eight lines. 

Table 4-2.  Change Notification Example

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