AI Interactive Datasheet ATmega16U2
AVR · megaAVR

ATmega16U2 registers

All 92 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.

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. 7PINC3
  2. 6PINC2
  3. 5PINC1
  4. 4PINC0
  5. 3–
  6. 2PINC2
  7. 1PINC1
  8. 0PINC0
2 fields
FieldBitsWhat it does
PINC7:4Port C Input Pins bits
PINC2:0Port C Input Pins bits

DDRCPort C Data Direction Register

Address
0x27 I/O 0x07
Reset
0x00
Access
read/write
  1. 7DDC3
  2. 6DDC2
  3. 5DDC1
  4. 4DDC0
  5. 3–
  6. 2DDC2
  7. 1DDC1
  8. 0DDC0
2 fields
FieldBitsWhat it does
DDC7:4Port C Data Direction Register bits
DDC2:0Port C Data Direction Register bits

PORTCPort C Data Register

Address
0x28 I/O 0x08
Reset
0x00
Access
read/write
  1. 7PORTC3
  2. 6PORTC2
  3. 5PORTC1
  4. 4PORTC0
  5. 3–
  6. 2PORTC2
  7. 1PORTC1
  8. 0PORTC0
2 fields
FieldBitsWhat it does
PORTC7:4Port C Data Register bits
PORTC2:0Port C Data Register bits

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. 7TCNT07
  2. 6TCNT06
  3. 5TCNT05
  4. 4TCNT04
  5. 3TCNT03
  6. 2TCNT02
  7. 1TCNT01
  8. 0TCNT00
1 field
FieldBitsWhat it does
TCNT07:0Timer/Counter0 bits

OCR0ATimer/Counter0 Output Compare Register

Address
0x47 I/O 0x27
Reset
0x00
Access
read/write
  1. 7OCR0A7
  2. 6OCR0A6
  3. 5OCR0A5
  4. 4OCR0A4
  5. 3OCR0A3
  6. 2OCR0A2
  7. 1OCR0A1
  8. 0OCR0A0
1 field
FieldBitsWhat it does
OCR0A7:0Timer/Counter0 Output Compare A bits

OCR0BTimer/Counter0 Output Compare Register

Address
0x48 I/O 0x28
Reset
0x00
Access
read/write
  1. 7OCR0B7
  2. 6OCR0B6
  3. 5OCR0B5
  4. 4OCR0B4
  5. 3OCR0B3
  6. 2OCR0B2
  7. 1OCR0B1
  8. 0OCR0B0
1 field
FieldBitsWhat it does
OCR0B7:0Timer/Counter0 Output Compare B bits

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/Counter1 Interrupt Flag register

Address
0x36 I/O 0x16
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5ICF1
  4. 4–
  5. 3OCF1C
  6. 2OCF1B
  7. 1OCF1A
  8. 0TOV1
5 fields
FieldBitsWhat it does
ICF15Input Capture Flag 1
OCF1C3Output Compare Flag 1C
OCF1B2Output Compare Flag 1B
OCF1A1Output Compare Flag 1A
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. 3OCIE1C
  6. 2OCIE1B
  7. 1OCIE1A
  8. 0TOIE1
5 fields
FieldBitsWhat it does
ICIE15Timer/Counter1 Input Capture Interrupt Enable
OCIE1C3Timer/Counter1 Output Compare C Match 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. 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

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
CS12:0Prescaler source of Timer/Counter 1
  • 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/Counter 1 Control Register C

Address
0x82
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 1A
FOC1B6Force Output Compare 1B
FOC1C5Force Output Compare 1C

TCNT1Timer/Counter1 Bytes

Address
0x84
Reset
0x0000
Access
read/write
Size
16-bit
1 field
FieldBitsWhat it does
TCNT115:0Timer/Counter1 bits

ICR1Timer/Counter1 Input Capture Register Bytes

Address
0x86
Reset
0x0000
Access
read/write
Size
16-bit
1 field
FieldBitsWhat it does
ICR115:0Timer/Counter1 Input Capture bits

OCR1ATimer/Counter1 Output Compare Register A Bytes

Address
0x88
Reset
0x0000
Access
read/write
Size
16-bit
1 field
FieldBitsWhat it does
OCR1A15:0Timer/Counter1 Output Compare A bits

OCR1BTimer/Counter1 Output Compare Register B Bytes

Address
0x8A
Reset
0x0000
Access
read/write
Size
16-bit
1 field
FieldBitsWhat it does
OCR1B15:0Timer/Counter1 Output Compare B bits

OCR1CTimer/Counter1 Output Compare Register C Bytes

Address
0x8C
Reset
0x0000
Access
read/write
Size
16-bit
1 field
FieldBitsWhat it does
OCR1C15:0Timer/Counter1 Output Compare C bits

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. 3–
  6. 2–
  7. 1PCIF1
  8. 0PCIF0
1 field
FieldBitsWhat it does
PCIF1:0Pin Change Interrupt Flags

EIFRExternal Interrupt Flag Register

Address
0x3C I/O 0x1C
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
0x3D I/O 0x1D
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

PCICRPin Change Interrupt Control Register

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

EICRAExternal Interrupt Control Register A

Address
0x69
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
ISC25:4External Interrupt Sense Control Bit
ISC13:2External Interrupt Sense Control Bit
ISC01:0External Interrupt Sense Control Bit

EICRBExternal Interrupt Control Register B

Address
0x6A
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
ISC65:4External Interrupt 7-4 Sense Control Bit
ISC53:2External Interrupt 7-4 Sense Control Bit
ISC41:0External Interrupt 7-4 Sense Control Bit

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. 7–
  2. 6–
  3. 5–
  4. 4PCINT4
  5. 3PCINT3
  6. 2PCINT2
  7. 1PCINT1
  8. 0PCINT0
1 field
FieldBitsWhat it does
PCINT4:0

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

DWDRdebugWire communication 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–

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 Reserved
  • 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. 5USBRF
  4. 4–
  5. 3WDRF
  6. 2BORF
  7. 1EXTRF
  8. 0PORF
5 fields
FieldBitsWhat it does
USBRF5USB 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. 7–
  2. 6–
  3. 5–
  4. 4PUD
  5. 3–
  6. 2–
  7. 1IVSEL
  8. 0IVCE
3 fields
FieldBitsWhat it does
PUD4Pull-up disable
IVSEL1Interrupt Vector Select
IVCE0Interrupt Vector Change Enable

EINDExtended Indirect Register

Address
0x5C I/O 0x3C
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0–

SPStack Pointer

Address
0x5D I/O 0x3D
Reset
0x02FF
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

PRR0Power Reduction Register0

Address
0x64
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5PRTIM0
  4. 4–
  5. 3PRTIM1
  6. 2PRSPI
  7. 1–
  8. 0–
3 fields
FieldBitsWhat it does
PRTIM05Power Reduction Timer/Counter0
PRTIM13Power Reduction Timer/Counter1
PRSPI2Power Reduction Serial Peripheral Interface

PRR1Power Reduction Register1

Address
0x65
Reset
0x00
Access
read/write
  1. 7PRUSB
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0PRUSART1
2 fields
FieldBitsWhat it does
PRUSB7Power Reduction USB
PRUSART10Power Reduction USART1

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

CLKSEL0

Address
0xD0
Reset
0x00
Access
read/write
  1. 7RCSUT1
  2. 6RCSUT0
  3. 5EXSUT1
  4. 4EXSUT0
  5. 3RCE
  6. 2EXTE
  7. 1–
  8. 0CLKS
5 fields
FieldBitsWhat it does
RCSUT7:6
EXSUT5:4
RCE3
EXTE2
CLKS0

CLKSEL1

Address
0xD1
Reset
0x00
Access
read/write
  1. 7RCCKSEL3
  2. 6RCCKSEL2
  3. 5RCCKSEL1
  4. 4RCCKSEL0
  5. 3EXCKSEL3
  6. 2EXCKSEL2
  7. 1EXCKSEL1
  8. 0EXCKSEL0
2 fields
FieldBitsWhat it does
RCCKSEL7:4
EXCKSEL3:0

CLKSTA

Address
0xD2
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1RCON
  8. 0EXTON
2 fields
FieldBitsWhat it does
RCON1
EXTON0

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. 7EEDR7
  2. 6EEDR6
  3. 5EEDR5
  4. 4EEDR4
  5. 3EEDR3
  6. 2EEDR2
  7. 1EEDR1
  8. 0EEDR0
1 field
FieldBitsWhat it does
EEDR7:0EEPROM Data bits

EEAREEPROM Address Register Low Bytes

Address
0x41 I/O 0x21
Reset
0x0000
Access
read/write
Size
16-bit
1 field
FieldBitsWhat it does
EEAR11:0EEPROM Address bits

PLL Phase Locked Loop

PLLCSRPLL Status and Control register

Address
0x49 I/O 0x29
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4PLLP2
  5. 3PLLP1
  6. 2PLLP0
  7. 1PLLE
  8. 0PLOCK
3 fields
FieldBitsWhat it does
PLLP4:2PLL prescaler Bits
  • 3 Clock/4
  • 5 Clock/8
PLLE1PLL Enable Bit
PLOCK0PLL Lock Status 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
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
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

SPDRSPI Data Register

Address
0x4E I/O 0x2E
Reset
0x00
Access
read/write
  1. 7SPDR7
  2. 6SPDR6
  3. 5SPDR5
  4. 4SPDR4
  5. 3SPDR3
  6. 2SPDR2
  7. 1SPDR1
  8. 0SPDR0
1 field
FieldBitsWhat it does
SPDR7:0SPI Data bits

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

ACMUXAnalog Comparator Input Multiplexer

Address
0x7D
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2CMUX2
  7. 1CMUX1
  8. 0CMUX0
1 field
FieldBitsWhat it does
CMUX2:0Analog Comparator Selection Bits
  • 0 AIN1
  • 1 AIN2
  • 2 AIN3
  • 3 AIN4
  • 4 AIN5
  • 5 AIN6

DIDR1

Address
0x7F
Reset
0x00
Access
read/write
  1. 7AIN7D
  2. 6AIN6D
  3. 5AIN5D
  4. 4AIN4D
  5. 3AIN3D
  6. 2AIN2D
  7. 1AIN1D
  8. 0AIN0D
8 fields
FieldBitsWhat it does
AIN7D7AIN7 Digital Input Disable
AIN6D6AIN6 Digital Input Disable
AIN5D5AIN5 Digital Input Disable
AIN4D4AIN4 Digital Input Disable
AIN3D3AIN3 Digital Input Disable
AIN2D2AIN2 Digital Input Disable
AIN1D1AIN1 Digital Input Disable
AIN0D0AIN0 Digital Input 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
WDCE4Watchdog Change Enable
WDE3Watch Dog Enable

WDTCKDWatchdog Timer Clock Divider

Address
0x62
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3WDEWIF
  6. 2WDEWIE
  7. 1WCLKD1
  8. 0WCLKD0
3 fields
FieldBitsWhat it does
WDEWIF3Watchdog Early Warning Interrupt Flag
WDEWIE2Watchdog Early Warning Interrupt Enable
WCLKD1:0Watchdog Timer Clock Dividers

USB_DEVICE USB Device Registers

REGCRRegulator Control Register

Address
0x63
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0REGDIS
1 field
FieldBitsWhat it does
REGDIS0Regulator Disable

USBCONUSB General Control Register

Address
0xD8
Reset
0x00
Access
read/write
  1. 7USBE
  2. 6–
  3. 5FRZCLK
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0–
2 fields
FieldBitsWhat it does
USBE7USB macro Enable Bit
FRZCLK5Freeze USB Clock Bit

UDCONUSB Device Control Registers

Address
0xE0
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2RSTCPU
  7. 1RMWKUP
  8. 0DETACH
3 fields
FieldBitsWhat it does
RSTCPU2USB Reset CPU Bit
RMWKUP1Remote Wake-up Bit
DETACH0Detach Bit

UDINTUSB Device Interrupt Register

Address
0xE1
Reset
0x00
Access
read/write
  1. 7–
  2. 6UPRSMI
  3. 5EORSMI
  4. 4WAKEUPI
  5. 3EORSTI
  6. 2SOFI
  7. 1–
  8. 0SUSPI
6 fields
FieldBitsWhat it does
UPRSMI6Upstream Resume Interrupt Flag
EORSMI5End Of Resume Interrupt Flag
WAKEUPI4Wake-up CPU Interrupt Flag
EORSTI3End Of Reset Interrupt Flag
SOFI2Start Of Frame Interrupt Flag
SUSPI0Suspend Interrupt Flag

UDIENUSB Device Interrupt Enable Register

Address
0xE2
Reset
0x00
Access
read/write
  1. 7–
  2. 6UPRSME
  3. 5EORSME
  4. 4WAKEUPE
  5. 3EORSTE
  6. 2SOFE
  7. 1–
  8. 0SUSPE
6 fields
FieldBitsWhat it does
UPRSME6Upstream Resume Interrupt Enable Bit
EORSME5End Of Resume Interrupt Enable Bit
WAKEUPE4Wake-up CPU Interrupt Enable Bit
EORSTE3End Of Reset Interrupt Enable Bit
SOFE2Start Of Frame Interrupt Enable Bit
SUSPE0Suspend Interrupt Enable Bit

UDADDRUSB Device Address Register

Address
0xE3
Reset
0x00
Access
read/write
  1. 7ADDEN
  2. 6UADD6
  3. 5UADD5
  4. 4UADD4
  5. 3UADD3
  6. 2UADD2
  7. 1UADD1
  8. 0UADD0
2 fields
FieldBitsWhat it does
ADDEN7Address Enable Bit
UADD6:0USB Address Bits

UDFNUMUSB Device Frame Number High Register

Address
0xE4
Reset
0x0000
Access
read/write
Size
16-bit
1 field
FieldBitsWhat it does
FNUM10:0Frame Number Upper Flag

UDMFNUSB Device Micro Frame Number

Address
0xE6
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4FNCERR
  5. 3–
  6. 2–
  7. 1–
  8. 0–
1 field
FieldBitsWhat it does
FNCERR4Frame Number CRC Error Flag

UEINTXUSB Endpoint Interrupt Register

Address
0xE8
Reset
0x00
Access
read/write
  1. 7FIFOCON
  2. 6NAKINI
  3. 5RWAL
  4. 4NAKOUTI
  5. 3RXSTPI
  6. 2RXOUTI
  7. 1STALLEDI
  8. 0TXINI
8 fields
FieldBitsWhat it does
FIFOCON7FIFO Control Bit
NAKINI6NAK IN Received Interrupt Flag
RWAL5Read/Write Allowed Flag
NAKOUTI4NAK OUT Received Interrupt Flag
RXSTPI3Received SETUP Interrupt Flag
RXOUTI2Received OUT Data Interrupt Flag
STALLEDI1STALLEDI Interrupt Flag
TXINI0Transmitter Ready Interrupt Flag

UENUMUSB Endpoint Number

Address
0xE9
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2EPNUM2
  7. 1EPNUM1
  8. 0EPNUM0
1 field
FieldBitsWhat it does
EPNUM2:0Endpoint Number bits

UERSTUSB Endpoint Reset Register

Address
0xEA
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4EPRST4
  5. 3EPRST3
  6. 2EPRST2
  7. 1EPRST1
  8. 0EPRST0
1 field
FieldBitsWhat it does
EPRST4:0Endpoint FIFO Reset Bits

UECONXUSB Endpoint Control Register

Address
0xEB
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5STALLRQ
  4. 4STALLRQC
  5. 3RSTDT
  6. 2–
  7. 1–
  8. 0EPEN
4 fields
FieldBitsWhat it does
STALLRQ5STALL Request Handshake Bit
STALLRQC4STALL Request Clear Handshake Bit
RSTDT3Reset Data Toggle Bit
EPEN0Endpoint Enable Bit

UECFG0XUSB Endpoint Configuration 0 Register

Address
0xEC
Reset
0x00
Access
read/write
  1. 7EPTYPE1
  2. 6EPTYPE0
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0EPDIR
2 fields
FieldBitsWhat it does
EPTYPE7:6Endpoint Type Bits
EPDIR0Endpoint Direction Bit

UECFG1XUSB Endpoint Configuration 1 Register

Address
0xED
Reset
0x00
Access
read/write
  1. 7–
  2. 6EPSIZE2
  3. 5EPSIZE1
  4. 4EPSIZE0
  5. 3EPBK1
  6. 2EPBK0
  7. 1ALLOC
  8. 0–
3 fields
FieldBitsWhat it does
EPSIZE6:4Endpoint Size Bits
EPBK3:2Endpoint Bank Bits
ALLOC1Endpoint Allocation Bit

UESTA0XUSB Endpoint Status 0 Register

Address
0xEE
Reset
0x00
Access
read/write
  1. 7CFGOK
  2. 6OVERFI
  3. 5UNDERFI
  4. 4–
  5. 3DTSEQ1
  6. 2DTSEQ0
  7. 1NBUSYBK1
  8. 0NBUSYBK0
5 fields
FieldBitsWhat it does
CFGOK7Configuration Status Flag
OVERFI6Overflow Error Interrupt Flag
UNDERFI5Underflow Error Interrupt Flag
DTSEQ3:2Data Toggle Sequencing Flag
NBUSYBK1:0Busy Bank Flag

UESTA1XUSB Endpoint Status 1 Register

Address
0xEF
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2CTRLDIR
  7. 1CURRBK1
  8. 0CURRBK0
2 fields
FieldBitsWhat it does
CTRLDIR2Control Direction
CURRBK1:0Current Bank

UEIENXUSB Endpoint Interrupt Enable Register

Address
0xF0
Reset
0x00
Access
read/write
  1. 7FLERRE
  2. 6NAKINE
  3. 5–
  4. 4NAKOUTE
  5. 3RXSTPE
  6. 2RXOUTE
  7. 1STALLEDE
  8. 0TXINE
7 fields
FieldBitsWhat it does
FLERRE7Flow Error Interrupt Enable Flag
NAKINE6NAK IN Interrupt Enable Bit
NAKOUTE4NAK OUT Interrupt Enable Bit
RXSTPE3Received SETUP Interrupt Enable Flag
RXOUTE2Received OUT Data Interrupt Enable Flag
STALLEDE1Stalled Interrupt Enable Flag
TXINE0Transmitter Ready Interrupt Enable Flag

UEDATXUSB Data Endpoint

Address
0xF1
Reset
0x00
Access
read/write
  1. 7DAT7
  2. 6DAT6
  3. 5DAT5
  4. 4DAT4
  5. 3DAT3
  6. 2DAT2
  7. 1DAT1
  8. 0DAT0
1 field
FieldBitsWhat it does
DAT7:0Data bits

UEBCLXUSB Endpoint Byte Count Register

Address
0xF2
Reset
0x00
Access
read/write
  1. 7BYCT7
  2. 6BYCT6
  3. 5BYCT5
  4. 4BYCT4
  5. 3BYCT3
  6. 2BYCT2
  7. 1BYCT1
  8. 0BYCT0
1 field
FieldBitsWhat it does
BYCT7:0Byte Count bits

UEINTUSB Endpoint Number Interrupt Register

Address
0xF4
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4EPINT4
  5. 3EPINT3
  6. 2EPINT2
  7. 1EPINT1
  8. 0EPINT0
1 field
FieldBitsWhat it does
EPINT4:0Byte Count bits

UPOEUSB Software Output Enable register

Address
0xFB
Reset
0x00
Access
read/write
  1. 7UPWE1
  2. 6UPWE0
  3. 5UPDRV1
  4. 4UPDRV0
  5. 3–
  6. 2–
  7. 1DPI
  8. 0DMI
4 fields
FieldBitsWhat it does
UPWE7:6USB Buffers Direct Drive enable configuration
UPDRV5:4USB direct drive values
DPI1D+ Input value
DMI0D- Input value

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
UPM15:4Parity Mode Bits
USBS13Stop Bit Select
UCSZ12:1Character Size
UCPOL10Clock Polarity

UCSR1DUSART Control and Status Register D

Address
0xCB
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1CTSEN
  8. 0RTSEN
2 fields
FieldBitsWhat it does
CTSEN1CTS Enable
RTSEN0RTS Enable

UBRR1USART Baud Rate Register Bytes

Address
0xCC
Reset
0x0000
Access
read/write
Size
16-bit
1 field
FieldBitsWhat it does
UBRR111:0USART Baud Rate bits

UDR1USART I/O Data Register

Address
0xCE
Reset
0x00
Access
read/write
  1. 7UDR17
  2. 6UDR16
  3. 5UDR15
  4. 4UDR14
  5. 3UDR13
  6. 2UDR12
  7. 1UDR11
  8. 0UDR10
1 field
FieldBitsWhat it does
UDR17:0USART I/O Data bits