ST9 Datasheet, PDF (83/146 Pages) STMicroelectronics – USER GUIDE

ST9 USER GUIDE
that are symmetrically centred on half of the reload value. For example, if the reload value is
255, the compare registers are set to the following values:
Duty Cycle
10%
25%
50%
75%
90%
Compare Register 0
115
96
64
32
13
Compare Register 1
140
159
191
223
242
You need to ensure that the compare registers are not written while they are used for a com-
parison. Because of this, they are written in an interrupt service routine that is triggered by the
MFT itself. To allow maximum latency time, the interrupt is triggered either by a compare 0 or
a compare 1 event, according to the value of the duty cycle. For duty cycles between 0 and
50%, the compare 0 event is used. Between 50% and 100%, the compare 1 event is used.
The following figures shows the timing diagram.
Figure 44. Output A Timing
Reload
Value
Compare
Register 1
Value
Compare
Register 0
Value
Output A
Reload
Interrupt
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