94
ATtiny25/45/85 [DATASHEET]
2586Q–AVR–08/2013
12.3.9
PLLCSR – PLL Control and Status Register
Bit 7 – LSM: Low Speed Mode
The high speed mode is enabled as default and the fast peripheral clock is 64 MHz, but the low speed mode can
be set by writing the LSM bit to one. Then the fast peripheral clock is scaled down to 32 MHz. The low speed mode
must be set, if the supply voltage is below 2.7 volts, because the Timer/Counter1 is not running fast enough on low
voltage levels. It is highly recommended that Timer/Counter1 is stopped whenever the LSM bit is changed.
Note, that LSM can not be set if PLL
CLK is used as system clock.
Bit 6:3 – Res : Reserved Bits
These bits are reserved bits in the ATtiny25/45/85 and always read as zero.
Bit 2 – PCKE: PCK Enable
The PCKE bit change the Timer/Counter1 clock source. When it is set, the asynchronous clock mode is enabled
and fast 64 MHz (or 32 MHz in Low Speed Mode) PCK clock is used as Timer/Counter1 clock source. If this bit is
cleared, the synchronous clock mode is enabled, and system clock CK is used as Timer/Counter1 clock source.
This bit can be set only if PLLE bit is set. It is safe to set this bit only when the PLL is locked i.e the PLOCK bit is 1.
The bit PCKE can only be set, if the PLL has been enabled earlier.
Bit 1 – PLLE: PLL Enable
When the PLLE is set, the PLL is started and if needed internal RC-oscillator is started as a PLL reference clock. If
PLL is selected as a system clock source the value for this bit is always 1.
Bit 0 – PLOCK: PLL Lock Detector
When the PLOCK bit is set, the PLL is locked to the reference clock. The PLOCK bit should be ignored during ini-
tial PLL lock-in sequence when PLL frequency overshoots and undershoots, before reaching steady state. The
steady state is obtained within 100 s. After PLL lock-in it is recommended to check the PLOCK bit before enabling
PCK for Timer/Counter1.
Bit
7
6
543
210
LSM
-
PCKE
PLLE
PLOCK
PLLCSR
Read/Write
R/W
R
R/W
R
Initial value
0
0/1
0