Chapter 4
Using the 6527
©
National Instruments Corporation
4-5
Figure 4-2.
Digital Filter Timing
Change Notification
You can program the 6527 to notify you of changes on input lines. Change
notification can reduce the number of reads your software must perform to
monitor inputs. Instead of reading the inputs continuously, your software
reacts only to transitions.
You can monitor changes on selected input lines or on all lines. You can
monitor for rising edges (0-to-1), falling edges (1-to-0), or both. When an
input change occurs matching your criteria, the 6527 generates an interrupt.
The NI-DAQ driver can then notify your software using a DAQ event or a
LabVIEW occurrence. See your software documentation for information
about support for event notification in your software environment.
The 6527 notifies you 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
The maximum rate of change notification is therefore limited by software response
time and varies from system to system.
Table 4-2 shows a change notification example for six 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
output device. The 6527 detects any change in the input data so you
can read the new data value.
External
Signal
External
Signal
Sampled
Filter
Clock
Sample Clock (100 ns)
Filtered
Signal
H
H
H
H
H
H
L
L
H
H
H
L
L
H
H
A
B
C
