Kuliah MikrokontrolerKuliah MikrokontrolerAVRAVR

Comparator AVRComparator AVR

Eru©September 2009Eru©September 2009PENSPENS

Analog ComparatorAnalog Comparator

The Analog Comparator compares the The Analog Comparator compares the input values on the positive pin AIN0 and input values on the positive pin AIN0 and negative pin AIN1.negative pin AIN1.When the voltage on the positive pin AIN0 When the voltage on the positive pin AIN0 is higher than the voltage on the negative is higher than the voltage on the negative pin AIN1, the Analog Comparator Output, pin AIN1, the Analog Comparator Output, ACO, is set.ACO, is set.The comparator’s output can be set to The comparator’s output can be set to trigger the Timer/Counter1 Input Capture trigger the Timer/Counter1 Input Capture function.function.

Analog Comparator (lanj.)Analog Comparator (lanj.)

In addition, the comparator can trigger a In addition, the comparator can trigger a separate interrupt, exclusive to the Analog separate interrupt, exclusive to the Analog Comparator.Comparator.The user can select Interrupt triggering on The user can select Interrupt triggering on comparator output rise, fall or toggle.comparator output rise, fall or toggle.A block diagram of the comparator and its A block diagram of the comparator and its surrounding logic is shown in Figure 21-1.surrounding logic is shown in Figure 21-1.

Analog Comparator Multiplexed Analog Comparator Multiplexed InputInput

It is possible to select any of the ADC7:0 pins to replace It is possible to select any of the ADC7:0 pins to replace the negative input to the Analog Comparator.the negative input to the Analog Comparator.The ADC multiplexer is used to select this input, and The ADC multiplexer is used to select this input, and consequently, the ADC must be switched off to utilize consequently, the ADC must be switched off to utilize this feature.this feature.If the Analog Comparator Multiplexer Enable bit (ACME If the Analog Comparator Multiplexer Enable bit (ACME in SFIOR) is set and the ADC is switched off (ADEN in in SFIOR) is set and the ADC is switched off (ADEN in ADCSRA is zero), MUX2:0 in ADMUX select the input ADCSRA is zero), MUX2:0 in ADMUX select the input pin to replace the negative input to the Analog pin to replace the negative input to the Analog Comparator, as shown in Table 1.Comparator, as shown in Table 1.If ACME is cleared or ADEN is set, AIN1 is applied to the If ACME is cleared or ADEN is set, AIN1 is applied to the negative input to the Analog Comparator.negative input to the Analog Comparator.

Register DescriptionRegister Description

SFIOR – Special Function IO RegisterSFIOR – Special Function IO RegisterACSR – Analog Comparator Control and ACSR – Analog Comparator Control and Status RegisterStatus Register

SFIOR – Special Function IO SFIOR – Special Function IO RegisterRegister

Bit 3 – ACME: Analog Comparator Bit 3 – ACME: Analog Comparator Multiplexer EnableMultiplexer Enable

Bit 3 – ACME: Analog Comparator Bit 3 – ACME: Analog Comparator Multiplexer EnableMultiplexer Enable

When this bit is written logic one and the When this bit is written logic one and the ADC is switched off (ADEN in ADCSRA is ADC is switched off (ADEN in ADCSRA is zero), thezero), theADC multiplexer selects the negative input ADC multiplexer selects the negative input to the Analog Comparator.to the Analog Comparator.When this bit is written logic zero, AIN1 is When this bit is written logic zero, AIN1 is applied to the negative input of the Analog applied to the negative input of the Analog Comparator.Comparator.For a detailed description of this bit, see For a detailed description of this bit, see “Analog Comparator Multiplexed Input” on “Analog Comparator Multiplexed Input” on page 204.page 204.

ACSR – Analog Comparator ACSR – Analog Comparator Control and Status RegisterControl and Status Register

Bit 7 – ACD: Analog Comparator DisableBit 7 – ACD: Analog Comparator DisableBit 6 – ACBG: Analog Comparator Bandgap SelectBit 6 – ACBG: Analog Comparator Bandgap SelectBit 5 – ACO: Analog Comparator OutputBit 5 – ACO: Analog Comparator OutputBit 4 – ACI: Analog Comparator Interrupt FlagBit 4 – ACI: Analog Comparator Interrupt FlagBit 3 – ACIE: Analog Comparator Interrupt EnableBit 3 – ACIE: Analog Comparator Interrupt EnableBit 2 – ACIC: Analog Comparator Input Capture EnableBit 2 – ACIC: Analog Comparator Input Capture EnableBits 1, 0 – ACIS1, ACIS0: Analog Comparator Interrupt Bits 1, 0 – ACIS1, ACIS0: Analog Comparator Interrupt Mode SelectMode Select

Bit 7 – ACD: Analog Comparator Bit 7 – ACD: Analog Comparator DisableDisable

When this bit is written logic one, the power to When this bit is written logic one, the power to the Analog Comparator is switched off.the Analog Comparator is switched off.This bit can be set at any time to turn off the This bit can be set at any time to turn off the Analog Comparator.Analog Comparator.This will reduce power consumption in active This will reduce power consumption in active and Idle mode.and Idle mode.When changing the ACD bit, the Analog When changing the ACD bit, the Analog Comparator Interrupt must beComparator Interrupt must bedisabled by clearing the ACIE bit in ACSR.disabled by clearing the ACIE bit in ACSR.– Otherwise an interrupt can occur when the bit is Otherwise an interrupt can occur when the bit is

changed.changed.

Bit 6 – ACBG: Analog Comparator Bit 6 – ACBG: Analog Comparator Bandgap SelectBandgap Select

When this bit is set, a fixed bandgap When this bit is set, a fixed bandgap reference voltage replaces the positive reference voltage replaces the positive input to the Analog Comparator.input to the Analog Comparator.When this bit is cleared, AIN0 is applied to When this bit is cleared, AIN0 is applied to the positive input of the Analog the positive input of the Analog Comparator.Comparator.See “Internal Voltage Reference” on page See “Internal Voltage Reference” on page 40.40.

Bit 5 – ACO: Analog Comparator Bit 5 – ACO: Analog Comparator OutputOutput

The output of the Analog Comparator is The output of the Analog Comparator is synchronized and then directly connected synchronized and then directly connected to ACO.to ACO.The synchronization introduces a delay of The synchronization introduces a delay of 1 - 2 clock cycles.1 - 2 clock cycles.

Bit 4 – ACI: Analog Comparator Bit 4 – ACI: Analog Comparator Interrupt FlagInterrupt Flag

This bit is set by hardware when a comparator This bit is set by hardware when a comparator output event triggers the interrupt mode defined output event triggers the interrupt mode defined by ACIS1 and ACIS0.by ACIS1 and ACIS0.The Analog Comparator Interrupt routine is The Analog Comparator Interrupt routine is executed if the ACIE bit is set and the I-bit in executed if the ACIE bit is set and the I-bit in SREG is set.SREG is set.ACI is cleared by hardware when executing the ACI is cleared by hardware when executing the corresponding interrupt handling vector.corresponding interrupt handling vector.Alternatively, ACI is cleared by writing a logic Alternatively, ACI is cleared by writing a logic one to the flag.one to the flag.

Bit 3 – ACIE: Analog Comparator Bit 3 – ACIE: Analog Comparator Interrupt EnableInterrupt Enable

When the ACIE bit is written logic one and When the ACIE bit is written logic one and the I-bit in the Status Register is set, the the I-bit in the Status Register is set, the Analog Comparator Interrupt is activated.Analog Comparator Interrupt is activated.When written logic zero, the interrupt is When written logic zero, the interrupt is disabled.disabled.

Bit 2 – ACIC: Analog Comparator Bit 2 – ACIC: Analog Comparator Input Capture EnableInput Capture Enable

When written logic one, this bit enables the Input When written logic one, this bit enables the Input Capture function in Timer/Counter1 to be triggered Capture function in Timer/Counter1 to be triggered by the Analog Comparator.by the Analog Comparator.The comparator output is in this case directly The comparator output is in this case directly connected to the Input Capture front-end logic, connected to the Input Capture front-end logic, making the comparator utilize the noise canceler making the comparator utilize the noise canceler and edge select features of the Timer/Counter1 and edge select features of the Timer/Counter1 Input Capture interrupt.Input Capture interrupt.When written logic zero, no connection between the When written logic zero, no connection between the Analog Comparator and the Input Capture function Analog Comparator and the Input Capture function exists.exists.To make the comparator trigger the Timer/Counter1 To make the comparator trigger the Timer/Counter1 Input Capture interrupt, the TICIE1 bit in the Timer Input Capture interrupt, the TICIE1 bit in the Timer Interrupt Mask Register (TIMSK) must be set.Interrupt Mask Register (TIMSK) must be set.

Bits 1, 0 – ACIS1, ACIS0: Analog Bits 1, 0 – ACIS1, ACIS0: Analog Comparator Interrupt Mode SelectComparator Interrupt Mode SelectThese bits determine which comparator These bits determine which comparator events that trigger the Analog Comparator events that trigger the Analog Comparator interrupt.interrupt.The different settings are shown in Table The different settings are shown in Table 21-1.21-1.When changing the ACIS1/ACIS0 bits, the When changing the ACIS1/ACIS0 bits, the Analog Comparator Interrupt must be Analog Comparator Interrupt must be disabled by clearing its Interrupt Enable bit disabled by clearing its Interrupt Enable bit in the ACSR Register.in the ACSR Register.– Otherwise an interrupt can occur when the Otherwise an interrupt can occur when the

bits are changed.bits are changed.