ATmega88PA Automotive Atmel Corporation, ATmega88PA Automotive Datasheet - Page 25

• Manufacturer Part Number: ATmega88PA Automotive
• Manufacturer: Atmel Corporation

7. System Clock and Clock Options
7.1
7.1.1
7.1.2
7.1.3
7701E–AVR–02/11
Clock Systems and their Distribution
CPU Clock – clk
I/O Clock – clk
Flash Clock – clk
I/O
CPU
Figure 7-1 on page 25
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, as described
in
Figure 7-1.
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 Status Register and the
Data memory holding the Stack Pointer. Halting the CPU clock inhibits the core from perform-
ing general operations and calculations.
The I/O clock is used by the majority of the I/O modules, like the 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.
The Flash clock controls operation of the Flash interface. The Flash clock is usually active
simultaneously with the CPU clock.
FLASH
“Power Management and Sleep Modes” on page
Clock Distribution
ADC
External Clock
clk
clk
ADC
I/O
Source clock
presents the principal clock systems in the AVR
General I/O
Atmel ATtiny24/44/84 [Preliminary]
System Clock
Modules
Control Unit
AVR Clock
Multiplexer
Prescaler
Clock
Calibrated RC
Oscillator
Oscillator
Crystal
Reset Logic
CPU Core
clk
clk
CPU
FLASH
Crystal Oscillator
Low-Frequency
Watchdog Timer
Watchdog clock
34. The clock systems are detailed below.
RAM
Watchdog
Oscillator
Flash and
EEPROM
®
Calibrated RC
and their distribution.
Oscillator
25