Texas Instruments MSP430x1xx - Manual (Page 148)

Timer Modes
10-8
10.3.2.1 Timer in Up Mode—Changing the Period Register CCR0 Value
Changing the timer period register CCR0 while the timer is running can be a
little tricky. When the new period is greater than or equal to the old period, the
timer simply
counts up to the new period and no special attention is required
(see Figure 10–7). However, when the new period is less than the old period,
the phase of the timer clock during the CCR0 update affects how the timer
reacts to the new period.
If the new, smaller period is written to CCR0 during a high phase of the timer
clock, then the timer rolls to zero (or begins counting down when in the
up/down mode) on the next rising edge of the timer clock. However, if the new,
smaller period is written during a low phase of the timer clock, then the timer
continues to increment with the old period for one more clock cycle before
adopting the new period and rolling to zero (or beginning counting down). This
is shown in Figure 10–8.
Figure 10–7. New Period > Old Period
2 0
ППППП
ППППП
0 1 1 2 3 0 1 2 3 0 1
2 3
CCR0old = 2
CCR0new = 3
3
2
1
0
CCR0
Timer
Register
Figure 10–8. New Period < Old Period
CCR0old = 5
CCR0new = 2
Timer
Register
5
4
3
2
1
0
0 1 2 3 4 5 0 1 2 3 0 1 2 0 1 2 0 1
5 2
0 1 2 3 4 5 0 1 2 3 4 0 1 2 0 1 2 0 1
5 2
Timer
Register
5
4
3
2
1
0
CCR0old = 5
CCR0new = 2
CCR0 CCR0
CCR0 Loaded With 2 During High Clock Phase CCR0 Loaded With 2 During Low Clock Phase
Timer Clock
Timer
CCR0
Timer Clock
Timer
CCR0
n 0 or n–1†
CCRold CCRnew CCRold CCRnew
n n+1 0 or n†
Load New CCR0
During High Phase of Clock
Load New CCR0
During Low Phase of Clock
† Up mode: 0; up/down mode: n–1 † Up mode: 0; up/down mode: n