AI Interactive Datasheet ATmega128
AVR · megaAVR

ATmega128 registers

All 103 registers by peripheral, at their data-space address (the I/O address IN and OUT use is shown beside it), with their reset value and every bit.

PORTF I/O Port

PINFInput Pins, Port F

Address
0x20 I/O 0x00
Reset
0x00
Access
read/write
  1. 7PINF7
  2. 6PINF6
  3. 5PINF5
  4. 4PINF4
  5. 3PINF3
  6. 2PINF2
  7. 1PINF1
  8. 0PINF0

DDRFData Direction Register, Port F

Address
0x61
Reset
0x00
Access
read/write
  1. 7DDF7
  2. 6DDF6
  3. 5DDF5
  4. 4DDF4
  5. 3DDF3
  6. 2DDF2
  7. 1DDF1
  8. 0DDF0

PORTFData Register, Port F

Address
0x62
Reset
0x00
Access
read/write
  1. 7PORTF7
  2. 6PORTF6
  3. 5PORTF5
  4. 4PORTF4
  5. 3PORTF3
  6. 2PORTF2
  7. 1PORTF1
  8. 0PORTF0

PORTE I/O Port

PINEInput Pins, Port E

Address
0x21 I/O 0x01
Reset
0x00
Access
read/write
  1. 7PINE7
  2. 6PINE6
  3. 5PINE5
  4. 4PINE4
  5. 3PINE3
  6. 2PINE2
  7. 1PINE1
  8. 0PINE0

DDREData Direction Register, Port E

Address
0x22 I/O 0x02
Reset
0x00
Access
read/write
  1. 7DDE7
  2. 6DDE6
  3. 5DDE5
  4. 4DDE4
  5. 3DDE3
  6. 2DDE2
  7. 1DDE1
  8. 0DDE0

PORTEData Register, Port E

Address
0x23 I/O 0x03
Reset
0x00
Access
read/write
  1. 7PORTE7
  2. 6PORTE6
  3. 5PORTE5
  4. 4PORTE4
  5. 3PORTE3
  6. 2PORTE2
  7. 1PORTE1
  8. 0PORTE0

ADC Analog-to-Digital Converter

ADCADC Data Register Bytes

Address
0x24 I/O 0x04
Reset
0x0000
Access
read/write
Size
16-bit

ADCSRAThe ADC Control and Status register

Address
0x26 I/O 0x06
Reset
0x00
Access
read/write
  1. 7ADEN
  2. 6ADSC
  3. 5ADFR
  4. 4ADIF
  5. 3ADIE
  6. 2ADPS2
  7. 1ADPS1
  8. 0ADPS0
6 fields
FieldBitsWhat it does
ADEN7ADC Enable
ADSC6ADC Start Conversion
ADFR5ADC Free Running Select
ADIF4ADC Interrupt Flag
ADIE3ADC Interrupt Enable
ADPS2:0ADC Prescaler Select Bits
  • 0 2
  • 1 2
  • 2 4
  • 3 8
  • 4 16
  • 5 32
  • 6 64
  • 7 128

ADMUXThe ADC multiplexer Selection Register

Address
0x27 I/O 0x07
Reset
0x00
Access
read/write
  1. 7REFS1
  2. 6REFS0
  3. 5ADLAR
  4. 4MUX4
  5. 3MUX3
  6. 2MUX2
  7. 1MUX1
  8. 0MUX0
3 fields
FieldBitsWhat it does
REFS7:6Reference Selection Bits
  • 0 AREF, Internal Vref turned off
  • 1 AVCC with external capacitor at AREF pin
  • 2 Reserved
  • 3 Internal 2.56V Voltage Reference with external capacitor at AREF pin
ADLAR5Left Adjust Result
MUX4:0Analog Channel and Gain Selection Bits

AC Analog Comparator

ACSRAnalog Comparator Control And Status Register

Address
0x28 I/O 0x08
Reset
0x00
Access
read/write
  1. 7ACD
  2. 6ACBG
  3. 5ACO
  4. 4ACI
  5. 3ACIE
  6. 2ACIC
  7. 1ACIS1
  8. 0ACIS0
7 fields
FieldBitsWhat it does
ACD7Analog Comparator Disable
ACBG6Analog Comparator Bandgap Select
ACO5Analog Compare Output
ACI4Analog Comparator Interrupt Flag
ACIE3Analog Comparator Interrupt Enable
ACIC2Analog Comparator Input Capture Enable
ACIS1:0Analog Comparator Interrupt Mode Select bits
  • 0 Interrupt on Toggle
  • 1 Reserved
  • 2 Interrupt on Falling Edge
  • 3 Interrupt on Rising Edge

SFIORSpecial Function IO Register

Address
0x40 I/O 0x20
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3ACME
  6. 2–
  7. 1–
  8. 0–
1 field
FieldBitsWhat it does
ACME3Analog Comparator Multiplexer Enable

USART0 USART

UBRR0LUSART Baud Rate Register Low Byte

Address
0x29 I/O 0x09
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0–

UCSR0BUSART Control and Status Register B

Address
0x2A I/O 0x0A
Reset
0x00
Access
read/write
  1. 7RXCIE0
  2. 6TXCIE0
  3. 5UDRIE0
  4. 4RXEN0
  5. 3TXEN0
  6. 2UCSZ02
  7. 1RXB80
  8. 0TXB80
8 fields
FieldBitsWhat it does
RXCIE07RX Complete Interrupt Enable
TXCIE06TX Complete Interrupt Enable
UDRIE05USART Data register Empty Interrupt Enable
RXEN04Receiver Enable
TXEN03Transmitter Enable
UCSZ022Character Size
RXB801Receive Data Bit 8
TXB800Transmit Data Bit 8

UCSR0AUSART Control and Status Register A

Address
0x2B I/O 0x0B
Reset
0x00
Access
read/write
  1. 7RXC0
  2. 6TXC0
  3. 5UDRE0
  4. 4FE0
  5. 3DOR0
  6. 2UPE0
  7. 1U2X0
  8. 0MPCM0
8 fields
FieldBitsWhat it does
RXC07USART Receive Complete
TXC06USART Transmit Complete
UDRE05USART Data Register Empty
FE04Framing Error
DOR03Data overRun
UPE02Parity Error
U2X01Double the USART transmission speed
MPCM00Multi-processor Communication Mode

UDR0USART I/O Data Register

Address
0x2C I/O 0x0C
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0–

UBRR0HUSART Baud Rate Register High Byte

Address
0x90
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0–

UCSR0CUSART Control and Status Register C

Address
0x95
Reset
0x00
Access
read/write
  1. 7–
  2. 6UMSEL0
  3. 5UPM01
  4. 4UPM00
  5. 3USBS0
  6. 2UCSZ01
  7. 1UCSZ00
  8. 0UCPOL0
5 fields
FieldBitsWhat it does
UMSEL06USART Mode Select
  • 0 Asynchronous Operation
  • 1 Synchronous Operation
UPM05:4Parity Mode Bits
  • 0 Disabled
  • 1 Reserved
  • 2 Enabled, Even Parity
  • 3 Enabled, Odd Parity
USBS03Stop Bit Select
  • 0 1-bit
  • 1 2-bit
UCSZ02:1Character Size
UCPOL00Clock Polarity

SPI Serial Peripheral Interface

SPCRSPI Control Register

Address
0x2D I/O 0x0D
Reset
0x00
Access
read/write
  1. 7SPIE
  2. 6SPE
  3. 5DORD
  4. 4MSTR
  5. 3CPOL
  6. 2CPHA
  7. 1SPR1
  8. 0SPR0
7 fields
FieldBitsWhat it does
SPIE7SPI Interrupt Enable
SPE6SPI Enable
DORD5Data Order
MSTR4Master/Slave Select
CPOL3Clock polarity
CPHA2Clock Phase
SPR1:0SPI Clock Rate Selects
  • 0 fosc/4
  • 1 fosc/16
  • 2 fosc/64
  • 3 fosc/128
  • 4 fosc/2
  • 5 fosc/8
  • 6 fosc/32
  • 7 fosc/64

SPSRSPI Status Register

Address
0x2E I/O 0x0E
Reset
0x00
Access
read/write
  1. 7SPIF
  2. 6WCOL
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0SPI2X
3 fields
FieldBitsWhat it does
SPIF7SPI Interrupt Flag
WCOL6Write Collision Flag
SPI2X0Double SPI Speed Bit

SPDRSPI Data Register

Address
0x2F I/O 0x0F
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0–

PORTD I/O Port

PINDPort D Input Pins

Address
0x30 I/O 0x10
Reset
0x00
Access
read/write
  1. 7PIND7
  2. 6PIND6
  3. 5PIND5
  4. 4PIND4
  5. 3PIND3
  6. 2PIND2
  7. 1PIND1
  8. 0PIND0

DDRDPort D Data Direction Register

Address
0x31 I/O 0x11
Reset
0x00
Access
read/write
  1. 7DDD7
  2. 6DDD6
  3. 5DDD5
  4. 4DDD4
  5. 3DDD3
  6. 2DDD2
  7. 1DDD1
  8. 0DDD0

PORTDPort D Data Register

Address
0x32 I/O 0x12
Reset
0x00
Access
read/write
  1. 7PORTD7
  2. 6PORTD6
  3. 5PORTD5
  4. 4PORTD4
  5. 3PORTD3
  6. 2PORTD2
  7. 1PORTD1
  8. 0PORTD0

PORTC I/O Port

PINCPort C Input Pins

Address
0x33 I/O 0x13
Reset
0x00
Access
read/write
  1. 7PINC7
  2. 6PINC6
  3. 5PINC5
  4. 4PINC4
  5. 3PINC3
  6. 2PINC2
  7. 1PINC1
  8. 0PINC0

DDRCPort C Data Direction Register

Address
0x34 I/O 0x14
Reset
0x00
Access
read/write
  1. 7DDC7
  2. 6DDC6
  3. 5DDC5
  4. 4DDC4
  5. 3DDC3
  6. 2DDC2
  7. 1DDC1
  8. 0DDC0

PORTCPort C Data Register

Address
0x35 I/O 0x15
Reset
0x00
Access
read/write
  1. 7PORTC7
  2. 6PORTC6
  3. 5PORTC5
  4. 4PORTC4
  5. 3PORTC3
  6. 2PORTC2
  7. 1PORTC1
  8. 0PORTC0

PORTB I/O Port

PINBPort B Input Pins

Address
0x36 I/O 0x16
Reset
0x00
Access
read/write
  1. 7PINB7
  2. 6PINB6
  3. 5PINB5
  4. 4PINB4
  5. 3PINB3
  6. 2PINB2
  7. 1PINB1
  8. 0PINB0

DDRBPort B Data Direction Register

Address
0x37 I/O 0x17
Reset
0x00
Access
read/write
  1. 7DDB7
  2. 6DDB6
  3. 5DDB5
  4. 4DDB4
  5. 3DDB3
  6. 2DDB2
  7. 1DDB1
  8. 0DDB0

PORTBPort B Data Register

Address
0x38 I/O 0x18
Reset
0x00
Access
read/write
  1. 7PORTB7
  2. 6PORTB6
  3. 5PORTB5
  4. 4PORTB4
  5. 3PORTB3
  6. 2PORTB2
  7. 1PORTB1
  8. 0PORTB0

PORTA I/O Port

PINAPort A Input Pins

Address
0x39 I/O 0x19
Reset
0x00
Access
read/write
  1. 7PINA7
  2. 6PINA6
  3. 5PINA5
  4. 4PINA4
  5. 3PINA3
  6. 2PINA2
  7. 1PINA1
  8. 0PINA0

DDRAPort A Data Direction Register

Address
0x3A I/O 0x1A
Reset
0x00
Access
read/write
  1. 7DDA7
  2. 6DDA6
  3. 5DDA5
  4. 4DDA4
  5. 3DDA3
  6. 2DDA2
  7. 1DDA1
  8. 0DDA0

PORTAPort A Data Register

Address
0x3B I/O 0x1B
Reset
0x00
Access
read/write
  1. 7PORTA7
  2. 6PORTA6
  3. 5PORTA5
  4. 4PORTA4
  5. 3PORTA3
  6. 2PORTA2
  7. 1PORTA1
  8. 0PORTA0

EEPROM EEPROM

EECREEPROM Control Register

Address
0x3C I/O 0x1C
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3EERIE
  6. 2EEMWE
  7. 1EEWE
  8. 0EERE
4 fields
FieldBitsWhat it does
EERIE3EEPROM Ready Interrupt Enable
EEMWE2EEPROM Master Write Enable
EEWE1EEPROM Write Enable
EERE0EEPROM Read Enable

EEDREEPROM Data Register

Address
0x3D I/O 0x1D
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0–

EEAREEPROM Read/Write Access Bytes

Address
0x3E I/O 0x1E
Reset
0x0000
Access
read/write
Size
16-bit

MISC Other Registers

SFIORSpecial Function IO Register

Address
0x40 I/O 0x20
Reset
0x00
Access
read/write
  1. 7TSM
  2. 6–
  3. 5–
  4. 4–
  5. 3ACME
  6. 2PUD
  7. 1PSR0
  8. 0PSR321
5 fields
FieldBitsWhat it does
TSM7Timer/Counter Synchronization Mode
ACME3Analog Comparator Multiplexer Enable
PUD2Pull Up Disable
PSR01Prescaler Reset Timer/Counter0
PSR3210Prescaler Reset Timer/Counter3, Timer/Counter2, and Timer/Counter1

TC0 Timer/Counter, 8-bit Async

SFIORSpecial Function IO Register

Address
0x40 I/O 0x20
Reset
0x00
Access
read/write
  1. 7TSM
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1PSR0
  8. 0–
2 fields
FieldBitsWhat it does
TSM7Timer/Counter Synchronization Mode
PSR01Prescaler Reset Timer/Counter0

ASSRAsynchronous Status Register

Address
0x50 I/O 0x30
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3AS0
  6. 2TCN0UB
  7. 1OCR0UB
  8. 0TCR0UB
4 fields
FieldBitsWhat it does
AS03Asynchronous Timer/Counter 0
TCN0UB2Timer/Counter0 Update Busy
OCR0UB1Output Compare register 0 Busy
TCR0UB0Timer/Counter Control Register 0 Update Busy

OCR0Output Compare Register

Address
0x51 I/O 0x31
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0–

TCNT0Timer/Counter Register

Address
0x52 I/O 0x32
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0–

TCCR0Timer/Counter Control Register

Address
0x53 I/O 0x33
Reset
0x00
Access
read/write
  1. 7FOC0
  2. 6WGM00
  3. 5COM01
  4. 4COM00
  5. 3WGM01
  6. 2CS02
  7. 1CS01
  8. 0CS00
5 fields
FieldBitsWhat it does
FOC07Force Output Compare
WGM006Waveform Generation Mode 0
  • 0 Normal
  • 1 CTC
  • 2 PWM, Phase Correct
  • 3 Fast PWM
COM05:4Compare Match Output Modes
WGM013Waveform Generation Mode 1
CS02:0Clock Selects
  • 0 No Clock Source (Stopped)
  • 1 Running, No Prescaling
  • 2 Running, CLK/8
  • 3 Running, CLK/32
  • 4 Running, CLK/64
  • 5 Running, CLK/128
  • 6 Running, CLK/256
  • 7 Running, CLK/1024

TIFRTimer/Counter Interrupt Flag register

Address
0x56 I/O 0x36
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1OCF0
  8. 0TOV0
2 fields
FieldBitsWhat it does
OCF01Output Compare Flag 0
TOV00Timer/Counter0 Overflow Flag

TIMSKTimer/Counter Interrupt Mask Register

Address
0x57 I/O 0x37
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1OCIE0
  8. 0TOIE0
2 fields
FieldBitsWhat it does
OCIE01Timer/Counter0 Output Compare Match Interrupt register
TOIE00Timer/Counter0 Overflow Interrupt Enable

TC1 Timer/Counter, 16-bit

SFIORSpecial Function IO Register

Address
0x40 I/O 0x20
Reset
0x00
Access
read/write
  1. 7TSM
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0PSR321
2 fields
FieldBitsWhat it does
TSM7Timer/Counter Synchronization Mode
PSR3210Prescaler Reset, T/C3, T/C2, T/C1

ICR1Timer/Counter1 Input Capture Register Bytes

Address
0x46 I/O 0x26
Reset
0x0000
Access
read/write
Size
16-bit

OCR1BTimer/Counter1 Output Compare Register Bytes

Address
0x48 I/O 0x28
Reset
0x0000
Access
read/write
Size
16-bit

OCR1ATimer/Counter1 Output Compare Register Bytes

Address
0x4A I/O 0x2A
Reset
0x0000
Access
read/write
Size
16-bit

TCNT1Timer/Counter1 Bytes

Address
0x4C I/O 0x2C
Reset
0x0000
Access
read/write
Size
16-bit

TCCR1BTimer/Counter1 Control Register B

Address
0x4E I/O 0x2E
Reset
0x00
Access
read/write
  1. 7ICNC1
  2. 6ICES1
  3. 5–
  4. 4WGM11
  5. 3WGM10
  6. 2CS12
  7. 1CS11
  8. 0CS10
4 fields
FieldBitsWhat it does
ICNC17Input Capture 1 Noise Canceler
ICES16Input Capture 1 Edge Select
WGM14:3Waveform Generation Mode
CS12:0Clock Select1 bits
  • 0 No Clock Source (Stopped)
  • 1 Running, No Prescaling
  • 2 Running, CLK/8
  • 3 Running, CLK/64
  • 4 Running, CLK/256
  • 5 Running, CLK/1024
  • 6 Running, ExtClk Tn Falling Edge
  • 7 Running, ExtClk Tn Rising Edge

TCCR1ATimer/Counter1 Control Register A

Address
0x4F I/O 0x2F
Reset
0x00
Access
read/write
  1. 7COM1A1
  2. 6COM1A0
  3. 5COM1B1
  4. 4COM1B0
  5. 3COM1C1
  6. 2COM1C0
  7. 1WGM11
  8. 0WGM10
4 fields
FieldBitsWhat it does
COM1A7:6Compare Output Mode 1A, bits
COM1B5:4Compare Output Mode 1B, bits
COM1C3:2Compare Output Mode 1C, bits
WGM11:0Waveform Generation Mode Bits

TIFRTimer/Counter Interrupt Flag register

Address
0x56 I/O 0x36
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5ICF1
  4. 4OCF1A
  5. 3OCF1B
  6. 2TOV1
  7. 1–
  8. 0–
4 fields
FieldBitsWhat it does
ICF15Input Capture Flag 1
OCF1A4Output Compare Flag 1A
OCF1B3Output Compare Flag 1B
TOV12Timer/Counter1 Overflow Flag

TIMSKTimer/Counter Interrupt Mask Register

Address
0x57 I/O 0x37
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5TICIE1
  4. 4OCIE1A
  5. 3OCIE1B
  6. 2TOIE1
  7. 1–
  8. 0–
4 fields
FieldBitsWhat it does
TICIE15Timer/Counter1 Input Capture Interrupt Enable
OCIE1A4Timer/Counter1 Output CompareA Match Interrupt Enable
OCIE1B3Timer/Counter1 Output CompareB Match Interrupt Enable
TOIE12Timer/Counter1 Overflow Interrupt Enable

OCR1CTimer/Counter1 Output Compare Register Bytes

Address
0x78
Reset
0x0000
Access
read/write
Size
16-bit

TCCR1CTimer/Counter1 Control Register C

Address
0x7A
Reset
0x00
Access
read/write
  1. 7FOC1A
  2. 6FOC1B
  3. 5FOC1C
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0–
3 fields
FieldBitsWhat it does
FOC1A7Force Output Compare for channel A
FOC1B6Force Output Compare for channel B
FOC1C5Force Output Compare for channel C

ETIFRExtended Timer/Counter Interrupt Flag register

Address
0x7C
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0OCF1C
1 field
FieldBitsWhat it does
OCF1C0Timer/Counter 1, Output Compare C Match Flag

ETIMSKExtended Timer/Counter Interrupt Mask Register

Address
0x7D
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0OCIE1C
1 field
FieldBitsWhat it does
OCIE1C0Timer/Counter 1, Output Compare Match C Interrupt Enable

TC3 Timer/Counter, 16-bit

SFIORSpecial Function IO Register

Address
0x40 I/O 0x20
Reset
0x00
Access
read/write
  1. 7TSM
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0PSR321
2 fields
FieldBitsWhat it does
TSM7Timer/Counter Synchronization Mode
PSR3210Prescaler Reset, T/C3, T/C2, T/C1

ETIFRExtended Timer/Counter Interrupt Flag register

Address
0x7C
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5ICF3
  4. 4OCF3A
  5. 3OCF3B
  6. 2TOV3
  7. 1OCF3C
  8. 0–
5 fields
FieldBitsWhat it does
ICF35Input Capture Flag 3
OCF3A4Output Compare Flag 3A
OCF3B3Output Compare Flag 3B
TOV32Timer/Counter3 Overflow Flag
OCF3C1Timer/Counter3 Output Compare C Match Flag

ETIMSKExtended Timer/Counter Interrupt Mask Register

Address
0x7D
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5TICIE3
  4. 4OCIE3A
  5. 3OCIE3B
  6. 2TOIE3
  7. 1OCIE3C
  8. 0–
5 fields
FieldBitsWhat it does
TICIE35Timer/Counter3 Input Capture Interrupt Enable
OCIE3A4Timer/Counter3 Output CompareA Match Interrupt Enable
OCIE3B3Timer/Counter3 Output CompareB Match Interrupt Enable
TOIE32Timer/Counter3 Overflow Interrupt Enable
OCIE3C1Timer/Counter3, Output Compare Match Interrupt Enable

ICR3Timer/Counter3 Input Capture Register Bytes

Address
0x80
Reset
0x0000
Access
read/write
Size
16-bit

OCR3CTimer/Counter3 Output compare Register C Bytes

Address
0x82
Reset
0x0000
Access
read/write
Size
16-bit

OCR3BTimer/Counter3 Output Compare Register B Bytes

Address
0x84
Reset
0x0000
Access
read/write
Size
16-bit

OCR3ATimer/Counter3 Output Compare Register A Bytes

Address
0x86
Reset
0x0000
Access
read/write
Size
16-bit

TCNT3Timer/Counter3 Bytes

Address
0x88
Reset
0x0000
Access
read/write
Size
16-bit

TCCR3BTimer/Counter3 Control Register B

Address
0x8A
Reset
0x00
Access
read/write
  1. 7ICNC3
  2. 6ICES3
  3. 5–
  4. 4WGM31
  5. 3WGM30
  6. 2CS32
  7. 1CS31
  8. 0CS30
4 fields
FieldBitsWhat it does
ICNC37Input Capture 3 Noise Canceler
ICES36Input Capture 3 Edge Select
WGM34:3Waveform Generation Mode
CS32:0Clock Select3 bits
  • 0 No Clock Source (Stopped)
  • 1 Running, No Prescaling
  • 2 Running, CLK/8
  • 3 Running, CLK/64
  • 4 Running, CLK/256
  • 5 Running, CLK/1024
  • 6 Running, ExtClk Tn Falling Edge
  • 7 Running, ExtClk Tn Rising Edge

TCCR3ATimer/Counter3 Control Register A

Address
0x8B
Reset
0x00
Access
read/write
  1. 7COM3A1
  2. 6COM3A0
  3. 5COM3B1
  4. 4COM3B0
  5. 3COM3C1
  6. 2COM3C0
  7. 1WGM31
  8. 0WGM30
4 fields
FieldBitsWhat it does
COM3A7:6Compare Output Mode 3A, bits
COM3B5:4Compare Output Mode 3B, bits
COM3C3:2Compare Output Mode 3C, bits
WGM31:0Waveform Generation Mode Bits

TCCR3CTimer/Counter3 Control Register C

Address
0x8C
Reset
0x00
Access
read/write
  1. 7FOC3A
  2. 6FOC3B
  3. 5FOC3C
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0–
3 fields
FieldBitsWhat it does
FOC3A7Force Output Compare for channel A
FOC3B6Force Output Compare for channel B
FOC3C5Force Output Compare for channel C

WDT Watchdog Timer

WDTCRWatchdog Timer Control Register

Address
0x41 I/O 0x21
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4WDCE
  5. 3WDE
  6. 2WDP2
  7. 1WDP1
  8. 0WDP0
3 fields
FieldBitsWhat it does
WDCE4Watchdog Change Enable
WDE3Watch Dog Enable
WDP2:0Watch Dog Timer Prescaler bits
  • 0 Oscillator Cycles 16K
  • 1 Oscillator Cycles 32K
  • 2 Oscillator Cycles 64K
  • 3 Oscillator Cycles 128K
  • 4 Oscillator Cycles 256K
  • 5 Oscillator Cycles 512K
  • 6 Oscillator Cycles 1024K
  • 7 Oscillator Cycles 2048K

JTAG JTAG Interface

OCDROn-Chip Debug Related Register in I/O Memory

Address
0x42 I/O 0x22
Reset
0x00
Access
read/write
  1. 7OCDR7
  2. 6OCDR6
  3. 5OCDR5
  4. 4OCDR4
  5. 3OCDR3
  6. 2OCDR2
  7. 1OCDR1
  8. 0OCDR0
1 field
FieldBitsWhat it does
OCDR7:0On-Chip Debug Register Bits

MCUCSRMCU Control And Status Register

Address
0x54 I/O 0x34
Reset
0x00
Access
read/write
  1. 7JTD
  2. 6–
  3. 5–
  4. 4JTRF
  5. 3–
  6. 2–
  7. 1–
  8. 0–
2 fields
FieldBitsWhat it does
JTD7JTAG Interface Disable
JTRF4JTAG Reset Flag

TC2 Timer/Counter, 8-bit

OCR2Output Compare Register

Address
0x43 I/O 0x23
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0–

TCNT2Timer/Counter Register

Address
0x44 I/O 0x24
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0–

TCCR2Timer/Counter Control Register

Address
0x45 I/O 0x25
Reset
0x00
Access
read/write
  1. 7FOC2
  2. 6WGM20
  3. 5COM21
  4. 4COM20
  5. 3WGM21
  6. 2CS22
  7. 1CS21
  8. 0CS20
5 fields
FieldBitsWhat it does
FOC27Force Output Compare
WGM206Waveform Generation Mode
  • 0 Normal
  • 1 CTC
  • 2 PWM, Phase Correct
  • 3 Fast PWM
COM25:4Compare Match Output Mode
WGM213Waveform Generation Mode
CS22:0Clock Select
  • 0 No Clock Source (Stopped)
  • 1 Running, No Prescaling
  • 2 Running, CLK/8
  • 3 Running, CLK/64
  • 4 Running, CLK/256
  • 5 Running, CLK/1024
  • 6 Running, ExtClk Tn Falling Edge
  • 7 Running, ExtClk Tn Rising Edge

TIFRTimer/Counter Interrupt Flag Register

Address
0x56 I/O 0x36
Reset
0x00
Access
read/write
  1. 7OCF2
  2. 6TOV2
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0–
2 fields
FieldBitsWhat it does
OCF27Output Compare Flag 2
TOV26Timer/Counter2 Overflow Flag

TIMSK

Address
0x57 I/O 0x37
Reset
0x00
Access
read/write
  1. 7OCIE2
  2. 6TOIE2
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0–
2 fields
FieldBitsWhat it does
OCIE27
TOIE26

CPU CPU Registers

MCUCSRMCU Control And Status Register

Address
0x54 I/O 0x34
Reset
0x00
Access
read/write
  1. 7JTD
  2. 6–
  3. 5–
  4. 4JTRF
  5. 3WDRF
  6. 2BORF
  7. 1EXTRF
  8. 0PORF
6 fields
FieldBitsWhat it does
JTD7JTAG Interface Disable
JTRF4JTAG Reset Flag
WDRF3Watchdog Reset Flag
BORF2Brown-out Reset Flag
EXTRF1External Reset Flag
PORF0Power-on reset flag

MCUCRMCU Control Register

Address
0x55 I/O 0x35
Reset
0x00
Access
read/write
  1. 7SRE
  2. 6SRW10
  3. 5SE
  4. 4SM1
  5. 3SM0
  6. 2SM2
  7. 1IVSEL
  8. 0IVCE
7 fields
FieldBitsWhat it does
SRE7External SRAM Enable
SRW106External SRAM Wait State Select
SE5Sleep Enable
SM4:3Sleep Mode Select
SM22Sleep Mode Select
  • 0 Idle
  • 2 ADC Noise Reduction (If Available)
  • 4 Power Down
  • 5 Standby
  • 6 Power Save
  • 7 Extended Standby
IVSEL1Interrupt Vector Select
IVCE0Interrupt Vector Change Enable

RAMPZRAM Page Z Select Register

Address
0x5B I/O 0x3B
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0RAMPZ0
1 field
FieldBitsWhat it does
RAMPZ00RAM Page Z Select Register Bit 0

XDIVXTAL Divide Control Register

Address
0x5C I/O 0x3C
Reset
0x00
Access
read/write
  1. 7XDIVEN
  2. 6XDIV6
  3. 5XDIV5
  4. 4XDIV4
  5. 3XDIV3
  6. 2XDIV2
  7. 1XDIV1
  8. 0XDIV0
8 fields
FieldBitsWhat it does
XDIVEN7XTAL Divide Enable
XDIV66XTAL Divide Select Bit 6
XDIV55XTAL Divide Select Bit 5
XDIV44XTAL Divide Select Bit 4
XDIV33XTAL Divide Select Bit 3
XDIV22XTAL Divide Select Bit 2
XDIV11XTAL Divide Select Bit 1
XDIV00XTAL Divide Select Bit 0

SPStack Pointer

Address
0x5D I/O 0x3D
Reset
0x10FF
Access
read/write
Size
16-bit

SREGStatus Register

Address
0x5F I/O 0x3F
Reset
0x00
Access
read/write
  1. 7I
  2. 6T
  3. 5H
  4. 4S
  5. 3V
  6. 2N
  7. 1Z
  8. 0C
8 fields
FieldBitsWhat it does
I7Global Interrupt Enable
T6Bit Copy Storage
H5Half Carry Flag
S4Sign Bit
V3Two's Complement Overflow Flag
N2Negative Flag
Z1Zero Flag
C0Carry Flag

XMCRBExternal Memory Control Register B

Address
0x6C
Reset
0x00
Access
read/write
  1. 7XMBK
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2XMM2
  7. 1XMM1
  8. 0XMM0
2 fields
FieldBitsWhat it does
XMBK7External Memory Bus Keeper Enable
XMM2:0External Memory High Mask

XMCRAExternal Memory Control Register A

Address
0x6D
Reset
0x00
Access
read/write
  1. 7–
  2. 6SRL2
  3. 5SRL1
  4. 4SRL0
  5. 3SRW01
  6. 2SRW00
  7. 1SRW11
  8. 0–
3 fields
FieldBitsWhat it does
SRL6:4Wait state page limit
  • 0 LS = N/A, US = 0x1100 - 0xFFFF
  • 1 LS = 0x1100 - 0x1FFF, US = 0x2000 - 0xFFFF
  • 2 LS = 0x1100 - 0x3FFF, US = 0x4000 - 0xFFFF
  • 3 LS = 0x1100 - 0x5FFF, US = 0x6000 - 0xFFFF
  • 4 LS = 0x1100 - 0x7FFF, US = 0x8000 - 0xFFFF
  • 5 LS = 0x1100 - 0x9FFF, US = 0xA000 - 0xFFFF
  • 6 LS = 0x1100 - 0xBFFF, US = 0xC000 - 0xFFFF
  • 7 LS = 0x1100 - 0xDFFF, US = 0xE000 - 0xFFFF
SRW03:2Wait state select bit lower page
  • 0 No wait-states
  • 1 Wait one cycle during read/write strobe
  • 2 Wait two cycles during read/write strobe
  • 3 Wait two cycles during read/write and wait one cycle before driving out new address
SRW111Wait state select bit upper page

OSCCALOscillator Calibration Value

Address
0x6F
Reset
0x00
Access
read/write
  1. 7OSCCAL7
  2. 6OSCCAL6
  3. 5OSCCAL5
  4. 4OSCCAL4
  5. 3OSCCAL3
  6. 2OSCCAL2
  7. 1OSCCAL1
  8. 0OSCCAL0
1 field
FieldBitsWhat it does
OSCCAL7:0Oscillator Calibration

EXINT External Interrupts

EIFRExternal Interrupt Flag Register

Address
0x58 I/O 0x38
Reset
0x00
Access
read/write
  1. 7INTF7
  2. 6INTF6
  3. 5INTF5
  4. 4INTF4
  5. 3INTF3
  6. 2INTF2
  7. 1INTF1
  8. 0INTF0
1 field
FieldBitsWhat it does
INTF7:0External Interrupt Flags

EIMSKExternal Interrupt Mask Register

Address
0x59 I/O 0x39
Reset
0x00
Access
read/write
  1. 7INT7
  2. 6INT6
  3. 5INT5
  4. 4INT4
  5. 3INT3
  6. 2INT2
  7. 1INT1
  8. 0INT0
1 field
FieldBitsWhat it does
INT7:0External Interrupt Request 7 Enable

EICRBExternal Interrupt Control Register B

Address
0x5A I/O 0x3A
Reset
0x00
Access
read/write
  1. 7ISC71
  2. 6ISC70
  3. 5ISC61
  4. 4ISC60
  5. 3ISC51
  6. 2ISC50
  7. 1ISC41
  8. 0ISC40
4 fields
FieldBitsWhat it does
ISC77:6External Interrupt 7-4 Sense Control Bit
  • 0 Low Level of INTX
  • 1 Any Logical Change of INTX
  • 2 Falling Edge of INTX
  • 3 Rising Edge of INTX
ISC65:4External Interrupt 7-4 Sense Control Bit
  • 0 Low Level of INTX
  • 1 Any Logical Change of INTX
  • 2 Falling Edge of INTX
  • 3 Rising Edge of INTX
ISC53:2External Interrupt 7-4 Sense Control Bit
  • 0 Low Level of INTX
  • 1 Any Logical Change of INTX
  • 2 Falling Edge of INTX
  • 3 Rising Edge of INTX
ISC41:0External Interrupt 7-4 Sense Control Bit
  • 0 Low Level of INTX
  • 1 Any Logical Change of INTX
  • 2 Falling Edge of INTX
  • 3 Rising Edge of INTX

EICRAExternal Interrupt Control Register A

Address
0x6A
Reset
0x00
Access
read/write
  1. 7ISC31
  2. 6ISC30
  3. 5ISC21
  4. 4ISC20
  5. 3ISC11
  6. 2ISC10
  7. 1ISC01
  8. 0ISC00
4 fields
FieldBitsWhat it does
ISC37:6External Interrupt Sense Control Bit
  • 0 Low Level of INTX
  • 1 Any Logical Change of INTX
  • 2 Falling Edge of INTX
  • 3 Rising Edge of INTX
ISC25:4External Interrupt Sense Control Bit
  • 0 Low Level of INTX
  • 1 Any Logical Change of INTX
  • 2 Falling Edge of INTX
  • 3 Rising Edge of INTX
ISC13:2External Interrupt Sense Control Bit
  • 0 Low Level of INTX
  • 1 Any Logical Change of INTX
  • 2 Falling Edge of INTX
  • 3 Rising Edge of INTX
ISC01:0External Interrupt Sense Control Bit
  • 0 Low Level of INTX
  • 1 Any Logical Change of INTX
  • 2 Falling Edge of INTX
  • 3 Rising Edge of INTX

PORTG I/O Port

PINGInput Pins, Port G

Address
0x63
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4PING4
  5. 3PING3
  6. 2PING2
  7. 1PING1
  8. 0PING0

DDRGData Direction Register, Port G

Address
0x64
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4DDG4
  5. 3DDG3
  6. 2DDG2
  7. 1DDG1
  8. 0DDG0

PORTGData Register, Port G

Address
0x65
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4PORTG4
  5. 3PORTG3
  6. 2PORTG2
  7. 1PORTG1
  8. 0PORTG0

BOOT_LOAD Bootloader

SPMCSRStore Program Memory Control Register

Address
0x68
Reset
0x00
Access
read/write
  1. 7SPMIE
  2. 6RWWSB
  3. 5–
  4. 4RWWSRE
  5. 3BLBSET
  6. 2PGWRT
  7. 1PGERS
  8. 0SPMEN
7 fields
FieldBitsWhat it does
SPMIE7SPM Interrupt Enable
RWWSB6Read While Write Section Busy
RWWSRE4Read While Write section read enable
BLBSET3Boot Lock Bit Set
PGWRT2Page Write
PGERS1Page Erase
SPMEN0Store Program Memory Enable

TWI Two Wire Serial Interface

TWBRTWI Bit Rate register

Address
0x70
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0–

TWSRTWI Status Register

Address
0x71
Reset
0x00
Access
read/write
  1. 7TWS4
  2. 6TWS3
  3. 5TWS2
  4. 4TWS1
  5. 3TWS0
  6. 2–
  7. 1TWPS1
  8. 0TWPS0
2 fields
FieldBitsWhat it does
TWS7:3TWI Status
TWPS1:0TWI Prescaler
  • 0 1
  • 1 4
  • 2 16
  • 3 64

TWARTWI (Slave) Address register

Address
0x72
Reset
0x00
Access
read/write
  1. 7TWA6
  2. 6TWA5
  3. 5TWA4
  4. 4TWA3
  5. 3TWA2
  6. 2TWA1
  7. 1TWA0
  8. 0TWGCE
2 fields
FieldBitsWhat it does
TWA7:1TWI (Slave) Address register Bits
TWGCE0TWI General Call Recognition Enable Bit

TWDRTWI Data register

Address
0x73
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0–

TWCRTWI Control Register

Address
0x74
Reset
0x00
Access
read/write
  1. 7TWINT
  2. 6TWEA
  3. 5TWSTA
  4. 4TWSTO
  5. 3TWWC
  6. 2TWEN
  7. 1–
  8. 0TWIE
7 fields
FieldBitsWhat it does
TWINT7TWI Interrupt Flag
TWEA6TWI Enable Acknowledge Bit
TWSTA5TWI Start Condition Bit
TWSTO4TWI Stop Condition Bit
TWWC3TWI Write Collision Flag
TWEN2TWI Enable Bit
TWIE0TWI Interrupt Enable

USART1 USART

UBRR1HUSART Baud Rate Register High Byte

Address
0x98
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0–

UBRR1LUSART Baud Rate Register Low Byte

Address
0x99
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0–

UCSR1BUSART Control and Status Register B

Address
0x9A
Reset
0x00
Access
read/write
  1. 7RXCIE1
  2. 6TXCIE1
  3. 5UDRIE1
  4. 4RXEN1
  5. 3TXEN1
  6. 2UCSZ12
  7. 1RXB81
  8. 0TXB81
8 fields
FieldBitsWhat it does
RXCIE17RX Complete Interrupt Enable
TXCIE16TX Complete Interrupt Enable
UDRIE15USART Data register Empty Interrupt Enable
RXEN14Receiver Enable
TXEN13Transmitter Enable
UCSZ122Character Size
RXB811Receive Data Bit 8
TXB810Transmit Data Bit 8

UCSR1AUSART Control and Status Register A

Address
0x9B
Reset
0x00
Access
read/write
  1. 7RXC1
  2. 6TXC1
  3. 5UDRE1
  4. 4FE1
  5. 3DOR1
  6. 2UPE1
  7. 1U2X1
  8. 0MPCM1
8 fields
FieldBitsWhat it does
RXC17USART Receive Complete
TXC16USART Transmit Complete
UDRE15USART Data Register Empty
FE14Framing Error
DOR13Data overRun
UPE12Parity Error
U2X11Double the USART transmission speed
MPCM10Multi-processor Communication Mode

UDR1USART I/O Data Register

Address
0x9C
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0–

UCSR1CUSART Control and Status Register C

Address
0x9D
Reset
0x00
Access
read/write
  1. 7–
  2. 6UMSEL1
  3. 5UPM11
  4. 4UPM10
  5. 3USBS1
  6. 2UCSZ11
  7. 1UCSZ10
  8. 0UCPOL1
5 fields
FieldBitsWhat it does
UMSEL16USART Mode Select
  • 0 Asynchronous Operation
  • 1 Synchronous Operation
UPM15:4Parity Mode Bits
  • 0 Disabled
  • 1 Reserved
  • 2 Enabled, Even Parity
  • 3 Enabled, Odd Parity
USBS13Stop Bit Select
  • 0 1-bit
  • 1 2-bit
UCSZ12:1Character Size
UCPOL10Clock Polarity