40
8008H–AVR–04/11
ATtiny48/88
7.4.2
MCUCR – MCU Control Register
Bits 7, 3:0 – Res: Reserved Bits
These bits are reserved and will always read zero.
Bit 6 – BODS: BOD Sleep
The BODS bit must be written to logic one in order to turn off BOD during sleep, see
Table 7-2on page 39. Writing to the BODS bit is controlled by a timed sequence and an enable bit,
BODSE in MCUCR. To disable BOD in relevant sleep modes, both BODS and BODSE must first
be set to one. Then, to set the BODS bit, BODS must be set to one and BODSE must be set to
zero within four clock cycles.
The BODS bit is active three clock cycles after it is set. A sleep instruction must be executed
while BODS is active in order to turn off the BOD for the actual sleep mode. The BODS bit is
automatically cleared after three clock cycles.
Bit 5 – BODSE: BOD Sleep Enable
BODSE enables setting of BODS control bit, as explained in BODS bit description. BOD disable
is controlled by a timed sequence.
7.4.3
PRR – Power Reduction Register
The Power Reduction Register (PRR) provides a method to stop the clock to individual peripher-
als to reduce power consumption. The current state of the peripheral is frozen and the I/O
registers can not be read or written. Resources used by the peripheral when stopping the clock
will remain occupied, hence the peripheral should in most cases be disabled before stopping the
clock. Waking up a module, which is done by clearing the bit in PRR, puts the module in the
same state as before shutdown.
Module shutdown can be used in Idle mode and Active mode to significantly reduce the overall
power consumption. In all other sleep modes, the clock is already stopped.
Bit 7 – PRTWI: Power Reduction TWI
Writing a logic one to this bit shuts down the TWI by stopping the clock to the module. When
waking up the TWI again, the TWI should be re initialized to ensure proper operation.
Bits 6, 4, 1 – Res: Reserved
These bits are reserved and will always read zero.
Bit 5 – PRTIM0: Power Reduction Timer/Counter0
Writing a logic one to this bit shuts down the Timer/Counter0 module. When the Timer/Counter0
is enabled, operation will continue like before the shutdown.
Bit
7
6
5
4
3
2
1
0
–
BODS
BODSE
PUD
–
MCUCR
Read/Write
R
R/W
R
Initial Value
0
Bit
7
6
5
4
3
210
PRTWI
–
PRTIM0
–
PRTIM1
PRSPI
–
PRADC
PRR
Read/Write
R/W
R
R/W
R
R/W
R
R/W
Initial Value
0