ELE22MIC Lecture 18• The AVR Sleep Modes

• The ATMEGA128’s Timer System– Clock Sources– The 8-bit Timer 0 Modes– Clear Timer on Compare match (CTC)– Two Pulse Width Modulation (PWM) modes

• Fast Pulse Width Modulation

• Phase Correct Pulse Width Modulation

8-bit Timer/Counter 0

• The ATMEGA128 contains 4 timer modules. The Bilby is the device we use in lab sessions: an ATMEGA128 on a PCB.

• Each module has a selection of possible clock or oscillator sources:– I/O Clock, System Clock

• The Bilby’s main crystal is 7.3728MHz,

– An External low-power crystal connected to TOSC1 & TOSC2 pins.

8-bit Timer/Counter 0• The Bilby’s main crystal is 7.3728MHz,

• ATMEGA128 Current consumption with the main oscillator running is in the order of 5mA.

• The Bilby’s low-power crystal connected to TOSC1 & TOSC2 pins.

• The Bilby’s low power crystal is 32768Hz • The ATMEGA128 has sleep modes where only this

counter remains active.• Total current consumption with a 32768Hz crystal clock

running, in power-down sleep mode, is around 200nA (all other subsystems switched off).

Modes of Sleep - Sleep Depth

Modes of Sleep - Clock Domains

Power-Save Considerations

Every enabled CPU feature consumes extra current.

For example the Bandgap voltage reference consumes 10uA current.

The ultra-low power-down sleep mode power consumption can only be achieved IF the features can be switched off.. We can then achieve ultra-low power operation - suitable for miniature battery operation.

Timer / Counter 0

• Main Features:

• Timer/Counter0 is a general purpose, single channel, 8-bit Timer/Counter module. The main features are:

• Single Channel Counter

• Clear Timer on Compare Match (Auto Reload)

Timer / Counter 0

• Glitch-free, Phase Correct Pulse Width Modulator (PWM)

• Frequency Generator

• 10-bit Clock Prescaler

• Overflow and Compare Match Interrupt Sources (TOV0 and OCF0)

• Allows Clocking from External 32 kHz Watch Crystal Independent of the I/O Clock

8-Bit Timer Block Diagram

8-Bit Timer Block Diagram

8-Bit Timer Counter Unit Block Diagram

8-Bit Timer Output Compare Unit

CTC Mode Timing Diagram

Fast PWM Mode, Timing Diagram

Phase Correct PWM Mode, Timing Diagram

ULN2003

Stepper Motor

ULN2003