Chapter4 Usingthe 6527
©NationalInstruments Corporation 4-5 6527User Manual
Figure4-2. DigitalFilter Timing
Change Notification
Youcan program the 6527 to notify you o f changes on input lines. Change
notificationcan reduce the number of read s your software must perform to
monitor inputs. Instead of reading the inputs continuously, your software
reactsonly to transitions.
Youcan monitor changes on selected input lines or on all lines. Youcan
monitor for rising edges (0-to-1), falling edges (1-to-0), or both. When an
inputchange occurs matching your criteria, the 6527 generates an interrupt.
The NI-DAQdriver can then notify your software using a DAQ eventor a
LabVIEW occurrence. See your software documentation for information
about support for eventnotification in your software environment.
The 6527 notifiesyou when any one of the changes you are monitoring
occurs; the 6527 does not report which line changed or whether the line
rose or fell. After a change, you can read the input lines to determine the
current line states.
Note Them aximum rate of change notification is therefore limited by software response
time and variesfrom system to system.
Table4-2 shows a change notification example for six bits of one port. This
exampleassumes the foll owingline connections:
•Bits 7, 6, 5, and 4 are connected to data lines from a four-bit TTL
output device.The 6527 detects any change in the input data so you
can read then ewdata value.
External
Signal
External
Signal
Sampled
Filter
Clock
SampleClock (100 ns)
Filtered
Signal
HHHHHHLLHH
HLLHH
A
B
C