AT90CAN128-16AE ATMEL Corporation, AT90CAN128-16AE Datasheet - Page 44

• 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

Power Management and Sleep Modes
Sleep Mode Control Register –
SMCR
44
AT90CAN128
Sleep modes enable the application to shut down unused modules in the MCU, thereby
saving power. The AVR provides various sleep modes allowing the user to tailor the
power consumption to the application’s requirements.
To enter any of the five sleep modes, the SE bit in SMCR must be written to logic one
and a SLEEP instruction must be executed. The SM2, SM1, and SM0 bits in the SMCR
Register select which sleep mode (Idle, ADC Noise Reduction, Power-down,
Power-save, or Standby) will be activated by the SLEEP instruction. See Table 17 for a
summary. If an enabled interrupt occurs while the MCU is in a sleep mode, the MCU
wakes up. The MCU is then halted for four cycles in addition to the start-up time, exe-
cutes the interrupt routine, and resumes execution from the instruction following SLEEP.
The contents of the register file and SRAM are unaltered when the device wakes up
from sleep. If a reset occurs during sleep mode, the MCU wakes up and executes from
the Reset Vector.
Figure 19 on page 35 presents the different clock systems in the AT90CAN128, and
their distribution. The figure is helpful in selecting an appropriate sleep mode.
The Sleep Mode Control Register contains control bits for power management.
• Bit 7..4 – Reserved Bits
These bits are reserved for future use.
• Bits 3..1 – SM2..0: Sleep Mode Select Bits 2, 1, and 0
These bits select between the five available sleep modes as shown in Table 17.
Table 17. Sleep Mode Select
Note:
• Bit 1 – SE: Sleep Enable
The SE bit must be written to logic one to make the MCU enter the sleep mode when the
SLEEP instruction is executed. To avoid the MCU entering the sleep mode unless it is
the programmer’s purpose, it is recommended to write the Sleep Enable (SE) bit to one
Bit
Read/Write
Initial Value
SM2
0
0
0
0
1
1
1
1
1. Standby mode is only recommended for use with external crystals or resonators.
R
7
–
0
SM1
0
0
1
1
0
0
1
1
R
6
–
0
R
5
–
0
SM0
0
1
0
1
0
1
0
1
R
4
–
0
Sleep Mode
Idle
ADC Noise Reduction
Power-down
Power-save
Reserved
Reserved
Standby
Reserved
SM2
R/W
3
0
(1)
SM1
R/W
2
0
SM0
R/W
1
0
R/W
SE
0
0
4250C–CAN–03/04
SMCR