The Counter period is changed by writing a
new TOP value to the Period register (TCA.PER).
No Buffering: If double buffering is not
used, any period update is immediate.
Figure 20-6. Changing the Period without
Buffering
A counter wraparound can occur in any mode
of operation when up-counting without buffering. This is due to the fact that the registers
TCA.CNT and TCA.PER are continuously compared: if a new TOP value is written to TCA.PER
that is lower than current TCA.CNT, the counter will wrap first before a compare match
happened.Figure 20-7. Unbuffered Dual-slope
Operation
With Buffering: When double
buffering is used, the buffer can be written at any time and still maintain correct
operation. The TCA.PER is always updated on the UPDATE condition, as shown for dual-slope
operation in the figure below. This prevents wraparound and the generation of odd
waveforms.Figure 20-8. Changing the Period Using
Buffering
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