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C161U
General Purpose Timer Unit
Data Sheet
227
2001-04-19
Table 40
Note:
Only state transitions of T3OTL which are caused by the overflows/underflows of
T3 will trigger the counter function of T4. Modifications of T3OTL via software will
NOT trigger the counter function of T4.
For counter operation, an external pin associated to line T4IN must be configured as
input. The maximum input frequency which is allowed in counter mode is
f
Timer
/8 (FM1 =
’1’). To ensure that a transition of the count input signal which is applied to T4IN is
correctly recognized, its level should be held for at least 4
f
Timer
cycles (FM1 = ’1’) before
it changes.
Timer T2 in Counter Mode
The operation of Timer T2 in counter mode is the same as described above for Timer T4
in Chapter "Timer T4 in Counter Mode", with the following exeption:
For Timer T2 there is no external input T2IN. Therefore, the counter function of T2 can
only be triggered by state transitions of T3OTL, which are caused by the overflows/
underflows of T3. Modifications of T3OTL via software will NOT trigger the counter
function of T2.
11.1.1.3
Timer Concatenation
Using the output toggle latch T3OTL as a clock source for an auxiliary timer in counter
mode concatenates the core timer T3 with the respective auxiliary timer. Depending on
which transition of T3OTL is selected to clock the auxiliary timer, this concatenation
forms a 32-bit or a 33-bit timer/counter.
32-bit Timer/Counter
: If both a positive and a negative transition of T3OTL is used to
clock the auxiliary timer, this timer is clocked on every overflow/underflow of the core
timer T3. Thus, the two timers form a 32-bit timer.
33-bit Timer/Counter
: If either a positive or a negative transition of T3OTL is selected
to clock the auxiliary timer, this timer is clocked on every second overflow/underflow of
Auxiliary Timer T4 (Counter Mode) Input Edge Selection
T4I
X 0 0
0 0 1
0 1 0
Triggering Edge for Counter Increment / Decrement
None. Counter T4 is disabled
Positive transition (rising edge) on T4IN
Negative transition (falling edge) on T4IN
0 1 1
1 0 1
1 1 0
1 1 1
Any transition (rising or falling edge) on T4IN
Positive transition (rising edge) of output toggle latch T3OTL
Negative transition (falling edge) of output toggle latch T3OTL
Any transition (rising or falling edge) of output toggle latch T3OTL