AT32UC3B0512_1 Datasheet, PDF (486/676 Pages) ATMEL Corporation – 32-bit AVR® Microcontroller

AT32UC3B
23.6.1.3
Clock selection
At block level, input clock signals of each channel can either be connected to the external inputs
TCLK0, TCLK1 or TCLK2, or be connected to the configurable I/O signals A0, A1 or A2 for
chaining by writing to the BMR register. See Figure 23-2 on page 486.
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. See the Module Configuration Chapter for details about
the connection of these clock sources.
• External clock signals: XC0, XC1 or XC2. See the Module Configuration Chapter for details
about the connection of these clock sources.
This selection is made by the Clock Selection field in the Channel n Mode Register
(CMRn.TCCLKS).
The selected clock can be inverted with the Clock Invert bit in CMRn (CMRn.CLKI). This allows
counting on the opposite edges of the clock.
The burst function allows the clock to be validated when an external signal is high. The Burst
Signal Selection field in the CMRn register (CMRn.BURST) defines this signal.
Note: In all cases, if an external clock is used, the duration of each of its levels must be longer than the
CLK_TC period. The external clock frequency must be at least 2.5 times lower than the CLK_TC.
Figure 23-2. Clock Selection
TCCLKS
TIMER_CLOCK1
TIMER_CLOCK2
TIMER_CLOCK3
TIMER_CLOCK4
TIMER_CLOCK5
XC0
XC1
XC2
CLKI
Selected
Clock
BURST
1
23.6.1.4
Clock control
The clock of each counter can be controlled in two different ways: it can be enabled/disabled
and started/stopped. See Figure 23-3 on page 487.
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