at91rm3400 ATMEL Corporation, at91rm3400 Datasheet - Page 346

• Manufacturer Part Number: at91rm3400
• Description: Atmel Advanced At91 Arm Microcontroller
• Manufacturer: ATMEL Corporation

Clock Control
346
AT91RM3400
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:
Figure 139. Clock Selection
The clock of each counter can be controlled in two different ways: it can be enabled/disabled
and started/stopped. See Figure 140.
•
•
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 TC_CMR. In Waveform Mode, it can be disabled by an RC
Compare event if CPCDIS is set to 1 in TC_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 (LDBSTOP = 1 in TC_CMR) or a RC compare event in Waveform Mode
(CPCSTOP = 1 in TC_CMR). The start and the stop commands have effect only if the
clock is enabled.
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
master clock
TIMER_CLOCK1
TIMER_CLOCK2
TIMER_CLOCK3
TIMER_CLOCK4
TIMER_CLOCK5
XC0
XC1
XC2
1
TCCLKS
BURST
CLKI
Selected
Clock
1790A–ATARM–11/03