Datasheet

27
ATtiny828 [DATASHEET]
8371A–AVR–08/12
6. Clock System
Figure 11 presents the principal clock systems and their distribution in ATtiny828. All of the clocks need not be active at
a given time. In order to reduce power consumption, the clocks to modules not being used can be halted by using
different sleep modes and power reduction register bits, as described in “Power Management and Sleep Modes” on page
34. The clock systems is detailed below.
Figure 11. Clock Distribution
6.1 Clock Subsystems
The clock subsystems are detailed in the sections below.
6.1.1 CPU Clock – clk
CPU
The CPU clock is routed to parts of the system concerned with operation of the AVR Core. Examples of such modules
are the General Purpose Register File, the System Registers and the SRAM data memory. Halting the CPU clock inhibits
the core from performing general operations and calculations.
6.1.2 I/O Clock – clk
I/O
The I/O clock is used by the majority of the I/O modules, like Timer/Counter. The I/O clock is also used by the External
Interrupt module, but note that some external interrupts are detected by asynchronous logic, allowing such interrupts to
be detected even if the I/O clock is halted.
6.1.3 NVM clock - clk
NVM
The NVM clock controls operation of the Non-Volatile Memory Controller. The NVM clock is usually active simultaneously
with the CPU clock.
CLOCK CONTROL UNIT
GENERAL
I/O MODULES
ANALOG-TO-DIGITAL
CONVERTER
CPU
CORE
WATCHDOG
TIMER
RESET
LOGIC
CLOCK
PRESCALER
RAM
CLOCK
SWITCH
NVM
CALIBRATED
OSCILLATOR
clk
ADC
SOURCE CLOCK
clk
I/O
clk
CPU
clk
NVM
WATCHDOG
CLOCK
ULTRA LOW POWER
OSCILLATOR
EXTERNAL
CLOCK