
153
2593O–AVR–02/12
ATmega644
rupt Enable), and TOV2 are set (one), the Timer/Counter2 Overflow interrupt is executed. In
PWM mode, this bit is set when Timer/Counter2 changes counting direction at 0x00.
15.11.9
GTCCR – General Timer/Counter Control Register
Bit 7 – TSM: Timer/Counter Synchronization Mode Writing the TSM bit to one activates the
Timer/Counter Synchronization mode. In this mode, the value that is written to the PSRASY
and PSRSYNC bits is kept, hence keeping the corresponding prescaler reset signals
asserted. This ensures that the corresponding Timer/Counters are halted and can be
configured to the same value without the risk of one of them advancing during configuration.
When the TSM bit is written to zero, the PSRASY and PSRSYNC bits are cleared by
hardware, and the Timer/Counters start counting simultaneously.
Bit 1 – PSRASY: Prescaler Reset Timer/Counter2
When this bit is one, the Timer/Counter2 prescaler will be reset. This bit is normally cleared
immediately by hardware. If the bit is written when Timer/Counter2 is operating in asynchronous
mode, the bit will remain one until the prescaler has been reset. The bit will not be cleared by
hardware if the TSM bit is set. Refer to the description of the “Bit 7 – TSM: Timer/Counter Syn-
chronization Mode” on page 136 for a description of the Timer/Counter Synchronization mode.
Bit 0– PSRSYNC :Prescaler Reset When this bit is one, Timer/Counter1 and Timer/Counter0
prescaler will be Reset. This bit is normally cleared immediately by hardware, except if the
TSM bit is set. Note that Timer/Counter1 and Timer/Counter0 share the same prescaler and a
reset of this prescaler will affect both timers.
Bit
7
6
5
4
3
2
1
0
TSM
–
PSRASY
PSRSYNC
GTCCR
Read/Write
R/W
R
R/W
Initial Value
0