Datasheet

119
8197C–AVR–05/11
ATtiny261A/461A/861A
the Output Compare Override Enable Bit is cleared. Table 12-22 shows the Output Compare
Override Enable Bits and their corresponding Output Compare pins.
12.12.6 PLLCSR – PLL Control and Status Register
• Bit 7 – LSM: Low Speed Mode
The Low Speed mode is set, if the LSM bit is written 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 recom-
mended that the Timer/Counter1 is stopped whenever the LSM bit is changed.
Note, that LSM can not be set if PLL
CLK
is used as a system clock.
• Bit 6:3 – Res : Reserved Bits
These bits are reserved and always read 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 a
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. It is safe to set this bit only when the
PLL is locked i.e the PLOCK bit is 1. Note that the PCKE bit can be set only, if the PLL has been
enabled earlier. The PLL is enabled when the CKSEL fuse has been programmed to 0x0001
(the PLL clock mode is selected) or the PLLE bit has been set to one.
• Bit 1 – PLLE: PLL Enable
When the PLLE is set, the PLL is started and if needed internal oscillator is started as a PLL ref-
erence 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.
Table 12-22. Output Compare Override Enable Bits vs. Output Compare Pins
Output CompareOverride Enable Bit Output Compare Output Output Compare Pin
OC1OE0 OC1A PB0
OC1OE1 OC1A PB1
OC1OE2 OC1B PB2
OC1OE3 OC1B PB3
OC1OE4 OC1D PB4
OC1OE5 OC1D PB5
Bit 76543210
0x29 (0x49) LSM––––PCKEPLLEPLOCKPLLCSR
Read/WriteR/WRRRRR/WR/WR
Initial value0000000/10