Saturday, 21 December 2013

SLEEP MODES IN AVR ATMEGA16 - DEMO - EXAMPLE CODE

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 six sleep modes, set the  SE bit in MCUCR and set the required sleep mode, then a SLEEP instruction must be executed.
     The SM2, SM1 and SM0 bits in the MCUCR Register select which sleep mode (Idle, ADC Noise Reduction, Power-down, Power-save, Standby, or Extended Standby) will be activated by the SLEEP instruction.

MCU Control Register – MCUCR

Bit

MCUCR

7

6

5

4

3

2

1

0

SM2

SE

SM1

SM0

ISC11

ISC10

ISC01

ISC00

Bit 7     – SE: Sleep Enable

Bits 6:4 – SM2..0: Sleep Mode Select Bits 2, 1, and 0

SM2

SM1

SM0

Sleep Mode

STOPED

Wake-Up INTERRUPT Source

0

0

0

Idle

CPU only 

External & all internal interrupts

(halts clkCPU and clkFLASH)

0

0

1

ADC Noise

Reduction

CPU & Timers 0,1

(halts clkI/O, clkCPU, and clkFLASH)

ADC Conversion Complete interrupt, only an External Reset, a Watchdog Reset, a Brown-out Reset, a Two-wire Serial Interface address match interrupt, a Timer/Counter2 interrupt, an SPM/EEPROM ready interrupt, or an external level interrupt on INT0 or INT1

0

1

0

Power-down#

External Oscillator Fclk & its functions

External Reset, a Watchdog Reset, a Brown-out Reset, a Two-wire Serial Interface address match interrupt, or an external level interrupt on INT0 or INT1

0

1

1

Power-save#

same as Power down except T2_Async

T2 Async INT, External Reset, a Watchdog Reset, a Brown-out Reset, a Two-wire Serial Interface address match interrupt, or an external level interrupt on INT0 or INT1

1

0

0

Reserved

1

0

1

1

1

0

Standby*

·     This mode is identical to Power-down, only if an* external crystal/resonator clock option is selected, with the exception that the Oscillator is kept running.

·     From Standby/Extended standby mode, the device wakes up in 6 clock cycles.

1

1

1

Extended

Standby

#- the wake up delay is according to start-up delay set by CKSEL fuses


Bit 3, 2  – ISC11, ISC10: Interrupt Sense Control 1 Bit 1 and Bit 0

Bit 1, 0  – ISC01, ISC00: Interrupt Sense Control 0 Bit 1 and Bit 0

 

Interrupt x (x=0 or 1) Sense Control

ISCx1

ISCx0

Description

0

0

The low level of INTx generates an interrupt request

0

1

Any logical change on INTx generates an interrupt request

1

0

The falling edge of INTx generates an interrupt request

1

1

The rising edge of INTx generates an interrupt request

 

General Interrupt Control Register – GICR

Bit 

7

6

5

4

3

2

1

0

INT1

INT0

INT2

IVSEL

IVCE

 

Bit 6 – INT0: External Interrupt Request 0 Enable   {0=disable, 1=ENABLED}


Here we present a simple GCC code done using AVR Studio4 in Atmega 16 MCU. The header file which is used for governing the sleep process is  <avr/sleep.h>.   Different Sleep modes are described in the previous table. External Interrupt0 is used as wake-up source.

Setting Sleep Mode:    set_sleep_mode(SLEEP_MODE_IDLE);
set_sleep_mode(MODE)
Arg: MODE=      SLEEP_MODE_IDLE
                            SLEEP_MODE_ADC
                            SLEEP_MODE_PWR_DOWN
                            SLEEP_MODE_PWR_SAVE   
                            SLEEP_MODE_STANDBY    
                            SLEEP_MODE_EXT_STANDBY

Entering Sleep Mode:     sleep_mode();

Setting INT0 interrupt:

//ext int0 @falling edge
 CLEARBIT(DDRD,2)
 SETBIT(PORTD,2)
 SETBIT(GICR,INT0)
 MCUCR|= ( (1<<ISC01)|(0<<ISC00) );

Enabling Global Interrupt:  sei();


        The code initializes the LCD display and sets INT0 in falling edge interrupt, IDLE sleep mode and enters sleep mode.
        When a falling edge on INT0 is detected INT0_ISR is executed which increments count variable & displays it on LCD. Then it returns to main function, which again enters into sleep mode. PB0 is set in ISR & cleared in main loop just for visual experience of ISR execution time.

Click here to download the code.

        The circuit for this demo is


        The Proteus Simulation output is...


This is an example implementation of Sleep mode. This sleep functions are common for most of the AVR MCU family, which will be taken care of <avr/sleep.h> header file.

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