Figure 1-3demonstrates 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
16 Installing and Configuring the HP E1459A
