attiny25v ATMEL Corporation, attiny25v Datasheet - Page 97

• Manufacturer Part Number: attiny25v
• Description: Microcontroller With 2/4/8k Bytes In-system Programmable Flash
• Manufacturer: ATMEL Corporation

12.3.9
2586K–AVR–01/08
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 recom-
mended that Timer/Counter1 is stopped whenever the LSM bit is changed.
Note, that LSM can not be set if PLL
• 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 initial PLL lock-in sequence when PLL frequency overshoots and undershoots,
before reaching steady state. The steady state is obtained within 100 µs. After PLL lock-in it is
recommended to check the PLOCK bit before enabling PCK for Timer/Counter1.
Bit
0x27
Read/Write
Initial value
LSM
R/W
7
0
R
6
0
-
R
5
0
-
CLK
is used as system clock.
R
4
0
-
R
3
0
-
PCKE
R/W
2
0
ATtiny25/45/85
PLLE
R/W
0/1
1
PLOCK
R
0
0
PLLCSR
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