AT32UC3A0512_1 Datasheet, PDF (642/826 Pages) ATMEL Corporation – AVR32 32-Bit Microcontroller

AT32UC3A
Each channel can independently select an internal or external clock source for its counter:
• Internal clock signals: TIMER_CLOCK1, TIMER_CLOCK2, TIMER_CLOCK3,
TIMER_CLOCK4, TIMER_CLOCK5. The Peripherals Chapter details the connection of these
clock sources.
• External clock signals: XC0, XC1 or XC2. The Peripherals Chapter details the connection of
these clock sources.
This selection is made by the TCCLKS bits in the TC Channel Mode Register .
The selected clock can be inverted with the CLKI bit in CMR. This allows counting on the oppo-
site edges of the clock.
The burst function allows the clock to be validated when an external signal is high. The BURST
parameter in the Mode Register defines this signal (none, XC0, XC1, XC2).
Note:
In all cases, if an external clock is used, the duration of each of its levels must be longer than the
master clock period. The external clock frequency must be at least 2.5 times lower than the mas-
ter clock
Figure 31-2. Clock Selection
TCCLKS
TIMER_CLOCK1
TIMER_CLOCK2
TIMER_CLOCK3
TIMER_CLOCK4
TIMER_CLOCK5
XC0
XC1
XC2
CLKI
Selected
Clock
BURST
1
31.6.1.3
Clock Control
The clock of each counter can be controlled in two different ways: it can be enabled/disabled
and started/stopped. See Figure 31-3.
• The clock can be enabled or disabled by the user with the CLKEN and the CLKDIS commands
in the Control Register. In Capture Mode it can be disabled by an RB load event if LDBDIS is
set to 1 in CMR. In Waveform Mode, it can be disabled by an RC Compare event if CPCDIS is
set to 1 in CMR. When disabled, the start or the stop actions have no effect: only a CLKEN
command in the Control Register can re-enable the clock. When the clock is enabled, the
CLKSTA bit is set in the Status Register.
• The clock can also be started or stopped: a trigger (software, synchro, external or compare)
always starts the clock. The clock can be stopped by an RB load event in Capture Mode
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