AI Interactive Datasheet ATmega164P
AVR · megaAVR

ATmega164P registers

All 96 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.

PORTA I/O Port

PINAPort A Input Pins

Address
0x20 I/O 0x00
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
0x21 I/O 0x01
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
0x22 I/O 0x02
Reset
0x00
Access
read/write
  1. 7PORTA7
  2. 6PORTA6
  3. 5PORTA5
  4. 4PORTA4
  5. 3PORTA3
  6. 2PORTA2
  7. 1PORTA1
  8. 0PORTA0

PORTB I/O Port

PINBPort B Input Pins

Address
0x23 I/O 0x03
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
0x24 I/O 0x04
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
0x25 I/O 0x05
Reset
0x00
Access
read/write
  1. 7PORTB7
  2. 6PORTB6
  3. 5PORTB5
  4. 4PORTB4
  5. 3PORTB3
  6. 2PORTB2
  7. 1PORTB1
  8. 0PORTB0

PORTC I/O Port

PINCPort C Input Pins

Address
0x26 I/O 0x06
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
0x27 I/O 0x07
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
0x28 I/O 0x08
Reset
0x00
Access
read/write
  1. 7PORTC7
  2. 6PORTC6
  3. 5PORTC5
  4. 4PORTC4
  5. 3PORTC3
  6. 2PORTC2
  7. 1PORTC1
  8. 0PORTC0

PORTD I/O Port

PINDPort D Input Pins

Address
0x29 I/O 0x09
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
0x2A I/O 0x0A
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
0x2B I/O 0x0B
Reset
0x00
Access
read/write
  1. 7PORTD7
  2. 6PORTD6
  3. 5PORTD5
  4. 4PORTD4
  5. 3PORTD3
  6. 2PORTD2
  7. 1PORTD1
  8. 0PORTD0

TC0 Timer/Counter, 8-bit

TIFR0Timer/Counter0 Interrupt Flag register

Address
0x35 I/O 0x15
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2OCF0B
  7. 1OCF0A
  8. 0TOV0
3 fields
FieldBitsWhat it does
OCF0B2Timer/Counter0 Output Compare Flag 0B
OCF0A1Timer/Counter0 Output Compare Flag 0A
TOV00Timer/Counter0 Overflow Flag

GTCCRGeneral Timer/Counter Control Register

Address
0x43 I/O 0x23
Reset
0x00
Access
read/write
  1. 7TSM
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0PSRSYNC
2 fields
FieldBitsWhat it does
TSM7Timer/Counter Synchronization Mode
PSRSYNC0Prescaler Reset Timer/Counter1 and Timer/Counter0

TCCR0ATimer/Counter Control Register A

Address
0x44 I/O 0x24
Reset
0x00
Access
read/write
  1. 7COM0A1
  2. 6COM0A0
  3. 5COM0B1
  4. 4COM0B0
  5. 3–
  6. 2–
  7. 1WGM01
  8. 0WGM00
3 fields
FieldBitsWhat it does
COM0A7:6Compare Output Mode, Phase Correct PWM Mode
COM0B5:4Compare Output Mode, Fast PWm
WGM01:0Waveform Generation Mode

TCCR0BTimer/Counter Control Register B

Address
0x45 I/O 0x25
Reset
0x00
Access
read/write
  1. 7FOC0A
  2. 6FOC0B
  3. 5–
  4. 4–
  5. 3WGM02
  6. 2CS02
  7. 1CS01
  8. 0CS00
4 fields
FieldBitsWhat it does
FOC0A7Force Output Compare A
FOC0B6Force Output Compare B
WGM023
CS02:0Clock 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

TCNT0Timer/Counter0

Address
0x46 I/O 0x26
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0–

OCR0ATimer/Counter0 Output Compare Register

Address
0x47 I/O 0x27
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0–

OCR0BTimer/Counter0 Output Compare Register

Address
0x48 I/O 0x28
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0–

TIMSK0Timer/Counter0 Interrupt Mask Register

Address
0x6E
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2OCIE0B
  7. 1OCIE0A
  8. 0TOIE0
3 fields
FieldBitsWhat it does
OCIE0B2Timer/Counter0 Output Compare Match B Interrupt Enable
OCIE0A1Timer/Counter0 Output Compare Match A Interrupt Enable
TOIE00Timer/Counter0 Overflow Interrupt Enable

TC1 Timer/Counter, 16-bit

TIFR1Timer/Counter Interrupt Flag register

Address
0x36 I/O 0x16
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5ICF1
  4. 4–
  5. 3–
  6. 2OCF1B
  7. 1OCF1A
  8. 0TOV1
4 fields
FieldBitsWhat it does
ICF15Timer/Counter1 Input Capture Flag
OCF1B2Timer/Counter1 Output Compare B Match Flag
OCF1A1Timer/Counter1 Output Compare A Match Flag
TOV10Timer/Counter1 Overflow Flag

TIMSK1Timer/Counter1 Interrupt Mask Register

Address
0x6F
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5ICIE1
  4. 4–
  5. 3–
  6. 2OCIE1B
  7. 1OCIE1A
  8. 0TOIE1
4 fields
FieldBitsWhat it does
ICIE15Timer/Counter1 Input Capture Interrupt Enable
OCIE1B2Timer/Counter1 Output Compare B Match Interrupt Enable
OCIE1A1Timer/Counter1 Output Compare A Match Interrupt Enable
TOIE10Timer/Counter1 Overflow Interrupt Enable

TCCR1ATimer/Counter1 Control Register A

Address
0x80
Reset
0x00
Access
read/write
  1. 7COM1A1
  2. 6COM1A0
  3. 5COM1B1
  4. 4COM1B0
  5. 3–
  6. 2–
  7. 1WGM11
  8. 0WGM10
3 fields
FieldBitsWhat it does
COM1A7:6Compare Output Mode 1A, bits
COM1B5:4Compare Output Mode 1B, bits
WGM11:0Pulse Width Modulator Select Bits

TCCR1BTimer/Counter1 Control Register B

Address
0x81
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 Bits
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

TCCR1CTimer/Counter1 Control Register C

Address
0x82
Reset
0x00
Access
read/write
  1. 7FOC1A
  2. 6FOC1B
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0–
2 fields
FieldBitsWhat it does
FOC1A7Force Output Compare for Channel A
FOC1B6Force Output Compare for Channel B

TCNT1Timer/Counter1 Bytes

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

ICR1Timer/Counter1 Input Capture Register Bytes

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

OCR1ATimer/Counter1 Output Compare Register A Bytes

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

OCR1BTimer/Counter1 Output Compare Register B Bytes

Address
0x8A
Reset
0x0000
Access
read/write
Size
16-bit

TC2 Timer/Counter, 8-bit Async

TIFR2Timer/Counter Interrupt Flag Register

Address
0x37 I/O 0x17
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2OCF2B
  7. 1OCF2A
  8. 0TOV2
3 fields
FieldBitsWhat it does
OCF2B2Output Compare Flag 2B
OCF2A1Output Compare Flag 2A
TOV20Timer/Counter2 Overflow Flag

GTCCRGeneral Timer Counter Control register

Address
0x43 I/O 0x23
Reset
0x00
Access
read/write
  1. 7TSM
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1PSRASY
  8. 0–
2 fields
FieldBitsWhat it does
TSM7Timer/Counter Synchronization Mode
PSRASY1Prescaler Reset Timer/Counter2

TIMSK2Timer/Counter Interrupt Mask register

Address
0x70
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2OCIE2B
  7. 1OCIE2A
  8. 0TOIE2
3 fields
FieldBitsWhat it does
OCIE2B2Timer/Counter2 Output Compare Match B Interrupt Enable
OCIE2A1Timer/Counter2 Output Compare Match A Interrupt Enable
TOIE20Timer/Counter2 Overflow Interrupt Enable

TCCR2ATimer/Counter2 Control Register A

Address
0xB0
Reset
0x00
Access
read/write
  1. 7COM2A1
  2. 6COM2A0
  3. 5COM2B1
  4. 4COM2B0
  5. 3–
  6. 2–
  7. 1WGM21
  8. 0WGM20
3 fields
FieldBitsWhat it does
COM2A7:6Compare Output Mode bits
COM2B5:4Compare Output Mode bits
WGM21:0Waveform Generation Mode

TCCR2BTimer/Counter2 Control Register B

Address
0xB1
Reset
0x00
Access
read/write
  1. 7FOC2A
  2. 6FOC2B
  3. 5–
  4. 4–
  5. 3WGM22
  6. 2CS22
  7. 1CS21
  8. 0CS20
4 fields
FieldBitsWhat it does
FOC2A7Force Output Compare A
FOC2B6Force Output Compare B
WGM223Waveform Generation Mode
CS22:0Clock Select bits
  • 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

TCNT2Timer/Counter2

Address
0xB2
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0–

OCR2ATimer/Counter2 Output Compare Register A

Address
0xB3
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0–

OCR2BTimer/Counter2 Output Compare Register B

Address
0xB4
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0–

ASSRAsynchronous Status Register

Address
0xB6
Reset
0x00
Access
read/write
  1. 7–
  2. 6EXCLK
  3. 5AS2
  4. 4TCN2UB
  5. 3OCR2AUB
  6. 2OCR2BUB
  7. 1TCR2AUB
  8. 0TCR2BUB
7 fields
FieldBitsWhat it does
EXCLK6Enable External Clock Input
AS25Asynchronous Timer/Counter2
TCN2UB4Timer/Counter2 Update Busy
OCR2AUB3Output Compare Register2 Update Busy
OCR2BUB2Output Compare Register 2 Update Busy
TCR2AUB1Timer/Counter Control Register2 Update Busy
TCR2BUB0Timer/Counter Control Register2 Update Busy

EXINT External Interrupts

PCIFRPin Change Interrupt Flag Register

Address
0x3B I/O 0x1B
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3PCIF3
  6. 2PCIF2
  7. 1PCIF1
  8. 0PCIF0
1 field
FieldBitsWhat it does
PCIF3:0Pin Change Interrupt Flags

EIFRExternal Interrupt Flag Register

Address
0x3C I/O 0x1C
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2INTF2
  7. 1INTF1
  8. 0INTF0
1 field
FieldBitsWhat it does
INTF2:0External Interrupt Flags

EIMSKExternal Interrupt Mask Register

Address
0x3D I/O 0x1D
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2INT2
  7. 1INT1
  8. 0INT0
1 field
FieldBitsWhat it does
INT2:0External Interrupt Request 2 Enable

PCICRPin Change Interrupt Control Register

Address
0x68
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3PCIE3
  6. 2PCIE2
  7. 1PCIE1
  8. 0PCIE0
1 field
FieldBitsWhat it does
PCIE3:0Pin Change Interrupt Enables

EICRAExternal Interrupt Control Register A

Address
0x69
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5ISC21
  4. 4ISC20
  5. 3ISC11
  6. 2ISC10
  7. 1ISC01
  8. 0ISC00
3 fields
FieldBitsWhat it does
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

PCMSK0Pin Change Mask Register 0

Address
0x6B
Reset
0x00
Access
read/write
  1. 7PCINT7
  2. 6PCINT6
  3. 5PCINT5
  4. 4PCINT4
  5. 3PCINT3
  6. 2PCINT2
  7. 1PCINT1
  8. 0PCINT0
1 field
FieldBitsWhat it does
PCINT7:0Pin Change Enable Masks

PCMSK1Pin Change Mask Register 1

Address
0x6C
Reset
0x00
Access
read/write
  1. 7PCINT7
  2. 6PCINT6
  3. 5PCINT5
  4. 4PCINT4
  5. 3PCINT3
  6. 2PCINT2
  7. 1PCINT1
  8. 0PCINT0
1 field
FieldBitsWhat it does
PCINT7:0Pin Change Enable Masks

PCMSK2Pin Change Mask Register 2

Address
0x6D
Reset
0x00
Access
read/write
  1. 7PCINT7
  2. 6PCINT6
  3. 5PCINT5
  4. 4PCINT4
  5. 3PCINT3
  6. 2PCINT2
  7. 1PCINT1
  8. 0PCINT0
1 field
FieldBitsWhat it does
PCINT7:0Pin Change Enable Masks

PCMSK3Pin Change Mask Register 3

Address
0x73
Reset
0x00
Access
read/write
  1. 7PCINT7
  2. 6PCINT6
  3. 5PCINT5
  4. 4PCINT4
  5. 3PCINT3
  6. 2PCINT2
  7. 1PCINT1
  8. 0PCINT0
1 field
FieldBitsWhat it does
PCINT7:0Pin Change Enable Masks

CPU CPU Registers

GPIOR0General Purpose IO Register 0

Address
0x3E I/O 0x1E
Reset
0x00
Access
read/write
  1. 7GPIOR07
  2. 6GPIOR06
  3. 5GPIOR05
  4. 4GPIOR04
  5. 3GPIOR03
  6. 2GPIOR02
  7. 1GPIOR01
  8. 0GPIOR00
8 fields
FieldBitsWhat it does
GPIOR077General Purpose IO Register 0 bit 7
GPIOR066General Purpose IO Register 0 bit 6
GPIOR055General Purpose IO Register 0 bit 5
GPIOR044General Purpose IO Register 0 bit 4
GPIOR033General Purpose IO Register 0 bit 3
GPIOR022General Purpose IO Register 0 bit 2
GPIOR011General Purpose IO Register 0 bit 1
GPIOR000General Purpose IO Register 0 bit 0

GPIOR1General Purpose IO Register 1

Address
0x4A I/O 0x2A
Reset
0x00
Access
read/write
  1. 7GPIOR7
  2. 6GPIOR6
  3. 5GPIOR5
  4. 4GPIOR4
  5. 3GPIOR3
  6. 2GPIOR2
  7. 1GPIOR1
  8. 0GPIOR0
1 field
FieldBitsWhat it does
GPIOR7:0General Purpose IO Register 1 bis

GPIOR2General Purpose IO Register 2

Address
0x4B I/O 0x2B
Reset
0x00
Access
read/write
  1. 7GPIOR7
  2. 6GPIOR6
  3. 5GPIOR5
  4. 4GPIOR4
  5. 3GPIOR3
  6. 2GPIOR2
  7. 1GPIOR1
  8. 0GPIOR0
1 field
FieldBitsWhat it does
GPIOR7:0General Purpose IO Register 2 bis

SMCRSleep Mode Control Register

Address
0x53 I/O 0x33
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3SM2
  6. 2SM1
  7. 1SM0
  8. 0SE
2 fields
FieldBitsWhat it does
SM3:1Sleep Mode Select bits
  • 0 Idle
  • 1 ADC Noise Reduction (If Available)
  • 2 Power Down
  • 3 Power Save
  • 4 Reserved
  • 5 Reserved
  • 6 Standby
  • 7 Extended Standby
SE0Sleep Enable

MCUSRMCU Status Register

Address
0x54 I/O 0x34
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4JTRF
  5. 3WDRF
  6. 2BORF
  7. 1EXTRF
  8. 0PORF
5 fields
FieldBitsWhat it does
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. 7JTD
  2. 6BODS
  3. 5BODSE
  4. 4PUD
  5. 3–
  6. 2–
  7. 1IVSEL
  8. 0IVCE
6 fields
FieldBitsWhat it does
JTD7JTAG Interface Disable
BODS6BOD Power Down in Sleep
BODSE5BOD Power Down in Sleep Enable
PUD4Pull-up disable
IVSEL1Interrupt Vector Select
IVCE0Interrupt Vector Change Enable

SPStack Pointer

Address
0x5D I/O 0x3D
Reset
0x04FF
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

CLKPR

Address
0x61
Reset
0x00
Access
read/write
  1. 7CLKPCE
  2. 6–
  3. 5–
  4. 4–
  5. 3CLKPS3
  6. 2CLKPS2
  7. 1CLKPS1
  8. 0CLKPS0
2 fields
FieldBitsWhat it does
CLKPCE7
CLKPS3:0
  • 0 1
  • 1 2
  • 2 4
  • 3 8
  • 4 16
  • 5 32
  • 6 64
  • 7 128
  • 8 256

PRR0Power Reduction Register0

Address
0x64
Reset
0x00
Access
read/write
  1. 7PRTWI
  2. 6PRTIM2
  3. 5PRTIM0
  4. 4PRUSART1
  5. 3PRTIM1
  6. 2PRSPI
  7. 1PRUSART0
  8. 0PRADC
8 fields
FieldBitsWhat it does
PRTWI7Power Reduction TWI
PRTIM26Power Reduction Timer/Counter2
PRTIM05Power Reduction Timer/Counter0
PRUSART14Power Reduction USART1
PRTIM13Power Reduction Timer/Counter1
PRSPI2Power Reduction Serial Peripheral Interface
PRUSART01Power Reduction USART0
PRADC0Power Reduction ADC

OSCCALOscillator Calibration Value

Address
0x66
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

EEPROM EEPROM

EECREEPROM Control Register

Address
0x3F I/O 0x1F
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5EEPM1
  4. 4EEPM0
  5. 3EERIE
  6. 2EEMPE
  7. 1EEPE
  8. 0EERE
5 fields
FieldBitsWhat it does
EEPM5:4EEPROM Programming Mode Bits
  • 0 Erase and Write in one operation
  • 1 Erase Only
  • 2 Write Only
EERIE3EEPROM Ready Interrupt Enable
EEMPE2EEPROM Master Write Enable
EEPE1EEPROM Write Enable
EERE0EEPROM Read Enable

EEDREEPROM Data Register

Address
0x40 I/O 0x20
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0–

EEAREEPROM Address Register Low Bytes

Address
0x41 I/O 0x21
Reset
0x0000
Access
read/write
Size
16-bit

SPI Serial Peripheral Interface

SPCRSPI Control Register

Address
0x4C I/O 0x2C
Reset
0x00
Access
read/write
  1. 7SPIE
  2. 6SPE
  3. 5DORD
  4. 4MSTR
  5. 3CPOL
  6. 2CPHA
  7. 1SPR1
  8. 0SPR0
8 fields
FieldBitsWhat it does
SPIE7SPI Interrupt Enable
SPE6SPI Enable
DORD5Data Order
MSTR4Master/Slave Select
CPOL3Clock polarity
CPHA2Clock Phase
SPR11SPI Clock Rate Select 1
SPR00SPI Clock Rate Select 0
  • 0 fosc/4
  • 1 fosc/16
  • 2 fosc/64
  • 3 fosc/128
  • 4 fosc/2
  • 5 fosc/8
  • 6 fosc/32
  • 7 fosc/64

SPCR0SPI Control Register

Address
0x4C I/O 0x2C
Reset
0x00
Access
read/write
  1. 7SPIE0
  2. 6SPE0
  3. 5DORD0
  4. 4MSTR0
  5. 3CPOL0
  6. 2CPHA0
  7. 1SPR10
  8. 0SPR00
8 fields
FieldBitsWhat it does
SPIE07SPI Interrupt Enable
SPE06SPI Enable
DORD05Data Order
MSTR04Master/Slave Select
CPOL03Clock polarity
CPHA02Clock Phase
SPR101SPI Clock Rate Select 1
SPR000SPI Clock Rate Select 0
  • 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
0x4D I/O 0x2D
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

SPSR0SPI Status Register

Address
0x4D I/O 0x2D
Reset
0x00
Access
read/write
  1. 7SPIF0
  2. 6WCOL0
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0SPI2X0
3 fields
FieldBitsWhat it does
SPIF07SPI Interrupt Flag
WCOL06Write Collision Flag
SPI2X00Double SPI Speed Bit

SPDRSPI Data Register

Address
0x4E I/O 0x2E
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0–

SPDR0SPI Data Register

Address
0x4E I/O 0x2E
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0–

AC Analog Comparator

ACSRAnalog Comparator Control And Status Register

Address
0x50 I/O 0x30
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

ADCSRBADC Control and Status Register B

Address
0x7B
Reset
0x00
Access
read/write
  1. 7–
  2. 6ACME
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0–
1 field
FieldBitsWhat it does
ACME6Analog Comparator Multiplexer Enable

DIDR1Digital Input Disable Register 1

Address
0x7F
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1AIN1D
  8. 0AIN0D
2 fields
FieldBitsWhat it does
AIN1D1AIN1 Digital Input Disable
AIN0D0AIN0 Digital Input Disable

JTAG JTAG Interface

OCDROn-Chip Debug Related Register in I/O Memory

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–

MCUSRMCU Status Register

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

MCUCRMCU Control Register

Address
0x55 I/O 0x35
Reset
0x00
Access
read/write
  1. 7JTD
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0–
1 field
FieldBitsWhat it does
JTD7JTAG Interface Disable

BOOT_LOAD Bootloader

SPMCSRStore Program Memory Control Register

Address
0x57 I/O 0x37
Reset
0x00
Access
read/write
  1. 7SPMIE
  2. 6RWWSB
  3. 5SIGRD
  4. 4RWWSRE
  5. 3BLBSET
  6. 2PGWRT
  7. 1PGERS
  8. 0SPMEN
8 fields
FieldBitsWhat it does
SPMIE7SPM Interrupt Enable
RWWSB6Read While Write Section Busy
SIGRD5Signature Row Read
RWWSRE4Read While Write section read enable
BLBSET3Boot Lock Bit Set
PGWRT2Page Write
PGERS1Page Erase
SPMEN0Store Program Memory Enable

WDT Watchdog Timer

WDTCSRWatchdog Timer Control Register

Address
0x60
Reset
0x00
Access
read/write
  1. 7WDIF
  2. 6WDIE
  3. 5WDP5
  4. 4WDCE
  5. 3WDE
  6. 2WDP2
  7. 1WDP1
  8. 0WDP0
5 fields
FieldBitsWhat it does
WDIF7Watchdog Timeout Interrupt Flag
WDIE6Watchdog Timeout Interrupt Enable
WDP5,2,1,0Watchdog Timer Prescaler Bits
  • 0 Oscillator Cycles 2K
  • 1 Oscillator Cycles 4K
  • 2 Oscillator Cycles 8K
  • 3 Oscillator Cycles 16K
  • 4 Oscillator Cycles 32K
  • 5 Oscillator Cycles 64K
  • 6 Oscillator Cycles 128K
  • 7 Oscillator Cycles 256K
  • 8 Oscillator Cycles 512K
  • 9 Oscillator Cycles 1024K
WDCE4Watchdog Change Enable
WDE3Watch Dog Enable

ADC Analog-to-Digital Converter

ADCADC Data Register Bytes

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

ADCSRAThe ADC Control and Status register A

Address
0x7A
Reset
0x00
Access
read/write
  1. 7ADEN
  2. 6ADSC
  3. 5ADATE
  4. 4ADIF
  5. 3ADIE
  6. 2ADPS2
  7. 1ADPS1
  8. 0ADPS0
6 fields
FieldBitsWhat it does
ADEN7ADC Enable
ADSC6ADC Start Conversion
ADATE5ADC Auto Trigger Enable
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

ADCSRBThe ADC Control and Status register B

Address
0x7B
Reset
0x00
Access
read/write
  1. 7–
  2. 6ACME
  3. 5–
  4. 4–
  5. 3–
  6. 2ADTS2
  7. 1ADTS1
  8. 0ADTS0
2 fields
FieldBitsWhat it does
ACME6
ADTS2:0ADC Auto Trigger Source bits
  • 0 Free Running mode
  • 1 Analog Comparator
  • 2 External Interrupt Request 0
  • 3 Timer/Counter0 Compare Match A
  • 4 Timer/Counter0 Overflow
  • 5 Timer/Counter1 Compare Match B
  • 6 Timer/Counter1 Overflow
  • 7 Timer/Counter1 Capture Event

ADMUXThe ADC multiplexer Selection Register

Address
0x7C
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 Internal 1.1V Voltage Reference with external capacitor at AREF pin
  • 3 Internal 2.56V Voltage Reference with external capacitor at AREF pin
ADLAR5Left Adjust Result
MUX4:0Analog Channel and Gain Selection Bits
  • 0 ADC Single Ended Input pin 0
  • 1 ADC Single Ended Input pin 1
  • 2 ADC Single Ended Input pin 2
  • 3 ADC Single Ended Input pin 3
  • 4 ADC Single Ended Input pin 4
  • 5 ADC Single Ended Input pin 5
  • 6 ADC Single Ended Input pin 6
  • 7 ADC Single Ended Input pin 7
  • 8 ADC Differential Inputs Positive pin 0 Negative pin 0 10x Gain
  • 9 ADC Differential Inputs Positive pin 1 Negative pin 0 10x Gain
  • 10 ADC Differential Inputs Positive pin 0 Negative pin 0 200x Gain
  • 11 ADC Differential Inputs Positive pin 1 Negative pin 0 200x Gain
  • 12 ADC Differential Inputs Positive pin 2 Negative pin 2 10x Gain
  • 13 ADC Differential Inputs Positive pin 3 Negative pin 2 10x Gain
  • 14 ADC Differential Inputs Positive pin 2 Negative pin 2 200x Gain
  • 15 ADC Differential Inputs Positive pin 3 Negative pin 2 200x Gain
  • 16 ADC Differential Inputs Positive pin 0 Negative pin 1 1x Gain
  • 17 ADC Differential Inputs Positive pin 1 Negative pin 1 1x Gain
  • 18 ADC Differential Inputs Positive pin 2 Negative pin 1 1x Gain
  • 19 ADC Differential Inputs Positive pin 3 Negative pin 1 1x Gain
  • 20 ADC Differential Inputs Positive pin 4 Negative pin 1 1x Gain
  • 21 ADC Differential Inputs Positive pin 5 Negative pin 1 1x Gain
  • 22 ADC Differential Inputs Positive pin 6 Negative pin 1 1x Gain
  • 23 ADC Differential Inputs Positive pin 7 Negative pin 1 1x Gain
  • 24 ADC Differential Inputs Positive pin 0 Negative pin 2 1x Gain
  • 25 ADC Differential Inputs Positive pin 1 Negative pin 2 1x Gain
  • 26 ADC Differential Inputs Positive pin 2 Negative pin 2 1x Gain
  • 27 ADC Differential Inputs Positive pin 3 Negative pin 2 1x Gain
  • 28 ADC Differential Inputs Positive pin 4 Negative pin 2 1x Gain
  • 29 ADC Differential Inputs Positive pin 5 Negative pin 2 1x Gain
  • 30 Internal Reference (VBG)
  • 31 0V (GND)

DIDR0Digital Input Disable Register

Address
0x7E
Reset
0x00
Access
read/write
  1. 7ADC7D
  2. 6ADC6D
  3. 5ADC5D
  4. 4ADC4D
  5. 3ADC3D
  6. 2ADC2D
  7. 1ADC1D
  8. 0ADC0D
8 fields
FieldBitsWhat it does
ADC7D7
ADC6D6
ADC5D5
ADC4D4
ADC3D3
ADC2D2
ADC1D1
ADC0D0

TWI Two Wire Serial Interface

TWBRTWI Bit Rate register

Address
0xB8
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
0xB9
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
0xBA
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
0xBB
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
0xBC
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

TWAMRTWI (Slave) Address Mask Register

Address
0xBD
Reset
0x00
Access
read/write
  1. 7TWAM6
  2. 6TWAM5
  3. 5TWAM4
  4. 4TWAM3
  5. 3TWAM2
  6. 2TWAM1
  7. 1TWAM0
  8. 0–
1 field
FieldBitsWhat it does
TWAM7:1

USART0 USART

UCSR0AUSART Control and Status Register A

Address
0xC0
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

UCSR0BUSART Control and Status Register B

Address
0xC1
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

UCSR0CUSART Control and Status Register C

Address
0xC2
Reset
0x00
Access
read/write
  1. 7UMSEL01
  2. 6UMSEL00
  3. 5UPM01
  4. 4UPM00
  5. 3USBS0
  6. 2UCSZ01
  7. 1UCSZ00
  8. 0UCPOL0
5 fields
FieldBitsWhat it does
UMSEL07:6USART Mode Select
  • 0 Asynchronous USART
  • 1 Synchronous USART
  • 3 Master SPI
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

UBRR0USART Baud Rate Register Bytes

Address
0xC4
Reset
0x0000
Access
read/write
Size
16-bit

UDR0USART I/O Data Register

Address
0xC6
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0–

USART1 USART

UCSR1AUSART Control and Status Register A

Address
0xC8
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

UCSR1BUSART Control and Status Register B

Address
0xC9
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

UCSR1CUSART Control and Status Register C

Address
0xCA
Reset
0x00
Access
read/write
  1. 7UMSEL11
  2. 6UMSEL10
  3. 5UPM11
  4. 4UPM10
  5. 3USBS1
  6. 2UCSZ11
  7. 1UCSZ10
  8. 0UCPOL1
5 fields
FieldBitsWhat it does
UMSEL17:6USART Mode Select
  • 0 Asynchronous USART
  • 1 Synchronous USART
  • 3 Master SPI
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

UBRR1USART Baud Rate Register Bytes

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

UDR1USART I/O Data Register

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