AT90CAN128-16AE ATMEL Corporation, AT90CAN128-16AE Datasheet - Page 35

• Manufacturer Part Number: AT90CAN128-16AE
• Description: 8-bit Avr Microcontroller With 128K Bytes of Isp Flash And CAN Controller.flash (Kbytes) 128 Vcc (V) 2.7-5.5 EEPROM (Kbytes) 4 SRAM (bytes) 4K CAN (mess. Obj.) 15
• Manufacturer: ATMEL Corporation

System Clock
Clock Systems and
their Distribution
CPU Clock – clk
I/O Clock – clk
Flash Clock – clk
Asynchronous Timer Clock –
clk
4250C–CAN–03/04
ASY
I/O
CPU
FLASH
Figure 19 presents the principal clock systems in the AVR and their distribution. All of
the clocks need not be active at a given time. In order to reduce power consumption, the
clocks to unused modules can be halted by using different sleep modes, as described in
“Power Management and Sleep Modes” on page 44. The clock systems are detailed
below.
Figure 19. Clock Distribution
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 Reg-
ister and the data memory holding the Stack Pointer. Halting the CPU clock inhibits the
core from performing general operations and calculations.
The I/O clock is used by the majority of the I/O modules, like Timer/Counters, SPI, CAN,
USART. 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. Also note that address recognition in the TWI
module is carried out asynchronously when clk
tion in all sleep modes.
The Flash clock controls operation of the Flash interface. The Flash clock is usually
active simultaneously with the CPU clock.
The Asynchronous Timer clock allows the Asynchronous Timer/Counter to be clocked
directly from an external clock or an external 32 kHz clock crystal. The dedicated clock
CLKO
Timer/Counter2
External Clock
Timer/Counter2
Asynchronous
CKOUT Fuse
Multiplexer
TOSC1
Timer/Counter2
Controller
Oscillator
CAN
TOSC2
General I/O
Modules
clk
External Clock
clk
ASY
I/O
Multiplexer
Control Unit
AVR Clock
Clock
ADC
I/O
clk
XTAL1
Source clock
ADC
is halted, enabling TWI address recep-
Oscillator
Crystal
XTAL2
CPU Core
clk
clk
Reset Logic
CPU
FLASH
AT90CAN128
Crystal Oscillator
Watchdog clock
Low-frequency
Watchdog Timer
RAM
Watchdog
Oscillator
Calibrated RC
Flash and
EEPROM
Oscillator
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