68HC11 Timing System
68HC11 Timing System
68HC11 Timing System
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Example 4.<br />
Determining the Period of a Square Wave.<br />
• The following program determines the period of a square wave<br />
by finding the time between rising edges.<br />
• The TCTL at $1021 is set up to detect rising edges on PA0.<br />
• Then the program jumps to SUB2, which clears the input capture<br />
flag IC3F, and waits until it is set again.<br />
• The time of its setting is stored in TIC3, at $1014 and $1015. This<br />
time is saved in memory (at location FIRST) and SUB2 is executed<br />
again to get the time of the next positive edge.<br />
• The difference between the times is a measure of pulse width.
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