HP E1459A, Руководство пользователя

Страница: 16 / 110

16 Installing and Configuring the HP E1459A
Edge Detection
Examples
Figure 1-3 demonstrates a typical example. A channel that has been
programmed to detect both positive and negative edge transitions posts a
marker at the occurrence of a positive edge. Before user software can service
this interrupt, a negative transition occurs and is detected. Because both are
detected and the events are marked, user software first reads the positive
edge detect register and then the negative edge detect register.
Figure 1-3. Positive and Negative Edge Transitions
In Figure 1-4, a channel that has been programmed for data capture posts a
marker on the occurrence of an external capture clock. During the
subsequent data register read cycle, another data capture clock occurs to
create a pending DAV (Data AVailable) situation. The second DAV is
retained (and valid) until a subsequent read of the corresponding data
register.
Figure 1-4. DAV Timing