ATtiny261-ESSZ datasheet(90/227 Pages) ATMEL

90 / 227 page

7753C–AVR–07/09

ATtiny261/ATtiny461/ATtiny861

15.1

15.1.1

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 bits in the ATtiny261/461/861 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 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 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.

15.1.2

TCCR1B – Timer/Counter1 Control Register B

• Bit 7 - Res: Reserved Bit

• Bit 6 - PSR1: Prescaler Reset Timer/Counter1

Bit

76543210

0x29 (0x49)

LSM

----PCKE

PLLE

PLOCK

PLLCSR

Read/Write

R/W

RRRRR/W

R/W

Initial value

0000000/1

Bit

543210

0x2F (0x4F)

PSR1

DTPS11

DTPS10

CS13

CS12

CS11

CS10

TCCR1B

Read/Write

R/W

Initial value

000000

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