In this 'Tips 'n Tricks' article from Microchip Technologies, the company describes a method of structuring faster code for detecting change.
When using a comparator to monitor a sensor, it is often just as important to know when a change occurs as it is to know what the change is. To detect a change in the output of a comparator, the traditional method has been to store a copy of the output and periodically compare the held value to the actual output to determine the change. An example of this type of routine is shown in Figure 1.
Figure 1. Routine 1
This routine requires five instructions for each test; nine instructions if a change occurs and one RAM location for storage of the old output state. A faster method for microcontrollers with a single comparator is to use the comparator interrupt-flag to determine when a change has occurred.
Routine 2 (Figure 2) requires two instructions for each test; three instructions if a change occurs and no RAM storage. If the interrupt flag cannot be used or if two comparators share an interrupt flag, an alternate method that uses the comparator output polarity bit can be used.
Figure 2. Routine 2
Routine 3 (Figure 3) requires two instructions for each test; five instructions if a change occurs and no GPR storage.
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