AI Interactive Datasheet ATtiny841
AVR · tinyAVR

ATtiny841 registers

All 101 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.

ADC Analog-to-Digital Converter

ADCSRBADC Control and Status Register B

Address
0x24 I/O 0x04
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3ADLAR
  6. 2ADTS2
  7. 1ADTS1
  8. 0ADTS0
2 fields
FieldBitsWhat it does
ADLAR3
ADTS2:0ADC Auto Trigger Sources
  • 0 Free Running mode
  • 1 Analog Comparator 0
  • 2 External Interrupt Request 0
  • 3 Timer/Counter0 Compare Match A
  • 4 Timer/Counter0 Overflow
  • 5 Timer/Counter1 Compare Match A
  • 6 Timer/Counter1 Overflow
  • 7 Timer/Counter1 Capture Event

ADCSRAThe ADC Control and Status register

Address
0x25 I/O 0x05
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

ADCADC Data Register Bytes

Address
0x26 I/O 0x06
Reset
0x0000
Access
read/write
Size
16-bit

ADMUXBThe ADC multiplexer Selection Register B

Address
0x28 I/O 0x08
Reset
0x00
Access
read/write
  1. 7REFS2
  2. 6REFS1
  3. 5REFS0
  4. 4–
  5. 3–
  6. 2–
  7. 1GSEL1
  8. 0GSEL0
2 fields
FieldBitsWhat it does
REFS7:5Reference Selection Bits
GSEL1:0Gain Selection Bits

ADMUXAThe ADC multiplexer Selection Register A

Address
0x29 I/O 0x09
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5MUX5
  4. 4MUX4
  5. 3MUX3
  6. 2MUX2
  7. 1MUX1
  8. 0MUX0
1 field
FieldBitsWhat it does
MUX5:0Analog Channel and Gain Selection Bits

DIDR0Digital Input Disable Register 0

Address
0x60
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
ADC7D7ADC7 Digital input Disable
ADC6D6ADC6 Digital input Disable
ADC5D5ADC5 Digital input Disable
ADC4D4ADC4/AIN11 Digital input Disable
ADC3D3ADC3/AIN10 Digital Input Disable
ADC2D2ADC2/AIN01 Digital input Disable
ADC1D1ADC1/AIN00 Digital input Disable
ADC0D0ADC0/AREF Digital input Disable

DIDR1Digital Input Disable Register 1

Address
0x61
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3ADC9D
  6. 2ADC8D
  7. 1ADC10D
  8. 0ADC11D
4 fields
FieldBitsWhat it does
ADC9D3ADC9 Digital Input Disable
ADC8D2ADC8 Digital input Disable
ADC10D1ADC10 Digital input Disable
ADC11D0ADC11 Digital input Disable

AC Analog Comparator

ACSR0AAnalog Comparator 0 Control And Status Register A

Address
0x2A I/O 0x0A
Reset
0x00
Access
read/write
  1. 7ACD0
  2. 6ACPMUX2
  3. 5ACO0
  4. 4ACI0
  5. 3ACIE0
  6. 2ACIC0
  7. 1ACIS01
  8. 0ACIS00
7 fields
FieldBitsWhat it does
ACD07Analog Comparator 0 Disable
ACPMUX26Analog Comparator 0 Positive Input Multiplexer Bit 2
ACO05Analog Comparator 0 Output
ACI04Analog Comparator 0 Interrupt Flag
ACIE03Analog Comparator 0 Interrupt Enable
ACIC02Analog Comparator 0 Input Capture Enable
ACIS01:0Analog Comparator 0 Interrupt Mode Select bits
  • 0 Interrupt on Toggle
  • 1 Reserved
  • 2 Interrupt on Falling Edge
  • 3 Interrupt on Rising Edge

ACSR0BAnalog Comparator 0 Control And Status Register B

Address
0x2B I/O 0x0B
Reset
0x00
Access
read/write
  1. 7HSEL0
  2. 6HLEV0
  3. 5–
  4. 4ACOE0
  5. 3ACNMUX1
  6. 2ACNMUX0
  7. 1ACPMUX1
  8. 0ACPMUX0
5 fields
FieldBitsWhat it does
HSEL07Analog Comparator 0 Hysteresis Select
HLEV06Analog Comparator 0 Hysteresis Level
ACOE04Analog Comparator 0 Output Pin Enable
ACNMUX3:2Analog Comparator 0 Negative Input Multiplexer
ACPMUX1:0Analog Comparator 0 Positive Input Multiplexer Bits 1:0

ACSR1AAnalog Comparator 1 Control And Status Register A

Address
0x2C I/O 0x0C
Reset
0x00
Access
read/write
  1. 7ACD1
  2. 6ACBG1
  3. 5ACO1
  4. 4ACI1
  5. 3ACIE1
  6. 2ACIC1
  7. 1ACIS11
  8. 0ACIS10
7 fields
FieldBitsWhat it does
ACD17Analog Comparator 1 Disable
ACBG16Analog Comparator 1 Bandgap Select
ACO15Analog Comparator 1 Output
ACI14Analog Comparator 1 Interrupt Flag
ACIE13Analog Comparator 1 Interrupt Enable
ACIC12Analog Comparator 1 Input Capture Enable
ACIS11:0Analog Comparator 1 Interrupt Mode Select bits
  • 0 Interrupt on Toggle
  • 1 Reserved
  • 2 Interrupt on Falling Edge
  • 3 Interrupt on Rising Edge

ACSR1BAnalog Comparator 1 Control And Status Register B

Address
0x2D I/O 0x0D
Reset
0x00
Access
read/write
  1. 7HSEL1
  2. 6HLEV1
  3. 5–
  4. 4ACOE1
  5. 3–
  6. 2ACME1
  7. 1–
  8. 0–
4 fields
FieldBitsWhat it does
HSEL17Analog Comparator 1 Hysteresis Select
HLEV16Analog Comparator 1 Hysteresis Level
ACOE14Analog Comparator 1 Output Pin Enable
ACME12Analog Comparator 1 Multiplexer Enable

TC1 Timer/Counter, 16-bit

TIFR1Timer/Counter Interrupt Flag register

Address
0x2E I/O 0x0E
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
0x2F I/O 0x0F
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

TCCR1CTimer/Counter1 Control Register C

Address
0x42 I/O 0x22
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

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. 0PSR
2 fields
FieldBitsWhat it does
TSM7Timer/Counter Synchronization Mode
PSR0Prescaler Reset Timer/CounterN

ICR1Timer/Counter1 Input Capture Register Bytes

Address
0x44 I/O 0x24
Reset
0x0000
Access
read/write
Size
16-bit

OCR1BTimer/Counter1 Output Compare Register B Bytes

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

OCR1ATimer/Counter1 Output Compare Register A 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 Bits
CS12:0Clock Select 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. 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

TC2 Timer/Counter, 16-bit

TIFR2Timer/Counter Interrupt Flag register

Address
0x30 I/O 0x10
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5ICF2
  4. 4–
  5. 3–
  6. 2OCF2B
  7. 1OCF2A
  8. 0TOV2
4 fields
FieldBitsWhat it does
ICF25Timer/Counter2 Input Capture Flag
OCF2B2Timer/Counter2 Output Compare B Match Flag
OCF2A1Timer/Counter2 Output Compare A Match Flag
TOV20Timer/Counter2 Overflow Flag

TIMSK2Timer/Counter2 Interrupt Mask Register

Address
0x31 I/O 0x11
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5ICIE2
  4. 4–
  5. 3–
  6. 2OCIE2B
  7. 1OCIE2A
  8. 0TOIE2
4 fields
FieldBitsWhat it does
ICIE25Timer/Counter2 Input Capture Interrupt Enable
OCIE2B2Timer/Counter2 Output Compare B Match Interrupt Enable
OCIE2A1Timer/Counter2 Output Compare A Match Interrupt Enable
TOIE20Timer/Counter2 Overflow Interrupt Enable

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. 0PSR
2 fields
FieldBitsWhat it does
TSM7Timer/Counter Synchronization Mode
PSR0Prescaler Reset Timer/CounterN

ICR2Timer/Counter2 Input Capture Register Bytes

Address
0xC0
Reset
0x0000
Access
read/write
Size
16-bit

OCR2BTimer/Counter2 Output Compare Register B Bytes

Address
0xC2
Reset
0x0000
Access
read/write
Size
16-bit

OCR2ATimer/Counter2 Output Compare Register A Bytes

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

TCNT2Timer/Counter2 Bytes

Address
0xC6
Reset
0x0000
Access
read/write
Size
16-bit

TCCR2CTimer/Counter2 Control Register C

Address
0xC8
Reset
0x00
Access
read/write
  1. 7FOC2A
  2. 6FOC2B
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0–
2 fields
FieldBitsWhat it does
FOC2A7Force Output Compare for Channel A
FOC2B6Force Output Compare for Channel B

TCCR2BTimer/Counter2 Control Register B

Address
0xC9
Reset
0x00
Access
read/write
  1. 7ICNC2
  2. 6ICES2
  3. 5–
  4. 4WGM21
  5. 3WGM20
  6. 2CS22
  7. 1CS21
  8. 0CS20
4 fields
FieldBitsWhat it does
ICNC27Input Capture 2 Noise Canceler
ICES26Input Capture 2 Edge Select
WGM24:3Waveform Generation Mode Bits
CS22:0Clock Select 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

TCCR2ATimer/Counter2 Control Register A

Address
0xCA
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 2A, bits
COM2B5:4Compare Output Mode 2B, bits
WGM21:0Pulse Width Modulator Select Bits

EXINT External Interrupts

PCMSK0Pin Change Enable Mask 0

Address
0x32 I/O 0x12
Reset
0x00
Access
read/write
  1. 7PCINT7
  2. 6PCINT6
  3. 5PCINT5
  4. 4PCINT4
  5. 3PCINT3
  6. 2PCINT2
  7. 1PCINT1
  8. 0PCINT0
8 fields
FieldBitsWhat it does
PCINT77Pin Change Enable Mask 0 Bit 7
PCINT66Pin Change Enable Mask 0 Bit 6
PCINT55Pin Change Enable Mask 0 Bit 5
PCINT44Pin Change Enable Mask 0 Bit 4
PCINT33Pin Change Enable Mask 0 Bit 3
PCINT22Pin Change Enable Mask 0 Bit 2
PCINT11Pin Change Enable Mask 0 Bit 1
PCINT00Pin Change Enable Mask 0 Bit 0

PCMSK1Pin Change Enable Mask 1

Address
0x40 I/O 0x20
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3PCINT11
  6. 2PCINT10
  7. 1PCINT9
  8. 0PCINT8
4 fields
FieldBitsWhat it does
PCINT113Pin Change Enable Mask 1 Bit 3
PCINT102Pin Change Enable Mask 1 Bit 2
PCINT91Pin Change Enable Mask 1 Bit 1
PCINT80Pin Change Enable Mask 1 Bit 0

MCUCRMCU Control Register

Address
0x55 I/O 0x35
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1ISC01
  8. 0ISC00
2 fields
FieldBitsWhat it does
ISC011Interrupt Sense Control 0 Bit 1
ISC000Interrupt Sense Control 0 Bit 0
  • 0 Low Level of INTX
  • 1 Reserved
  • 2 Falling Edge of INTX
  • 3 Rising Edge of INTX

GIFRGeneral Interrupt Flag register

Address
0x5A I/O 0x3A
Reset
0x00
Access
read/write
  1. 7–
  2. 6INTF0
  3. 5PCIF1
  4. 4PCIF0
  5. 3–
  6. 2–
  7. 1–
  8. 0–
2 fields
FieldBitsWhat it does
INTF06External Interrupt Flag 0
PCIF5:4Pin Change Interrupt Flags

GIMSKGeneral Interrupt Mask Register

Address
0x5B I/O 0x3B
Reset
0x00
Access
read/write
  1. 7–
  2. 6INT0
  3. 5PCIE1
  4. 4PCIE0
  5. 3–
  6. 2–
  7. 1–
  8. 0–
2 fields
FieldBitsWhat it does
INT06External Interrupt Request 0 Enable
PCIE5:4Pin Change Interrupt Enables

CPU CPU Registers

GPIOR0General Purpose I/O Register 0

Address
0x33 I/O 0x13
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0–

GPIOR1General Purpose I/O Register 1

Address
0x34 I/O 0x14
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0–

GPIOR2General Purpose I/O Register 2

Address
0x35 I/O 0x15
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. 4–
  5. 3WDRF
  6. 2BORF
  7. 1EXTRF
  8. 0PORF
4 fields
FieldBitsWhat it does
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. 5SE
  4. 4SM1
  5. 3SM0
  6. 2–
  7. 1ISC01
  8. 0ISC00
3 fields
FieldBitsWhat it does
SE5Sleep Enable
SM4:3Sleep Mode Select Bits
  • 0 Idle
  • 1 ADC Noise Reduction (If Available)
  • 2 Power Down
  • 3 Standby
ISC01:0Interrupt Sense Control 0 bits

SPMCSRStore Program Memory Control and Status Register

Address
0x57 I/O 0x37
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5RSIG
  4. 4CTPB
  5. 3RFLB
  6. 2PGWRT
  7. 1PGERS
  8. 0SPMEN
6 fields
FieldBitsWhat it does
RSIG5Read Device Signature Imprint Table
CTPB4Clear Temporary Page Buffer
RFLB3Read Fuse and Lock Bits
PGWRT2Page Write
PGERS1Page Erase
SPMEN0Store program Memory Enable

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

PRRPower Reduction Register

Address
0x70
Reset
0x00
Access
read/write
  1. 7PRTWI
  2. 6PRUSART1
  3. 5PRUSART0
  4. 4PRSPI
  5. 3PRTIM2
  6. 2PRTIM1
  7. 1PRTIM0
  8. 0PRADC
8 fields
FieldBitsWhat it does
PRTWI7Power Reduction TWI
PRUSART16Power Reduction USART1
PRUSART05Power Reduction USART0
PRSPI4Power Reduction SPI
PRTIM23Power Reduction Timer/Counter2
PRTIM12Power Reduction Timer/Counter1
PRTIM01Power Reduction Timer/Counter0
PRADC0Power Reduction ADC

CCPConfiguration Change Protection

Address
0x71
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0–

CLKCRClock Control Register

Address
0x72
Reset
0x00
Access
read/write
  1. 7OSCRDY
  2. 6CSTR
  3. 5CKOUTC
  4. 4SUT
  5. 3CKSEL3
  6. 2CKSEL2
  7. 1CKSEL1
  8. 0CKSEL0
5 fields
FieldBitsWhat it does
OSCRDY7Oscillator Ready
CSTR6Clock Switch Trigger
CKOUTC5Clock Output (Copy). Active low.
SUT4Start-up Time
CKSEL3:0Clock Select Bits

CLKPRClock Prescale Register

Address
0x73
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3CLKPS3
  6. 2CLKPS2
  7. 1CLKPS1
  8. 0CLKPS0
1 field
FieldBitsWhat it does
CLKPS3:0Clock Prescaler Select Bits
  • 0 1
  • 1 2
  • 2 4
  • 3 8
  • 4 16
  • 5 32
  • 6 64
  • 7 128
  • 8 256

OSCCAL0Oscillator Calibration Register 8MHz

Address
0x74
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0–

OSCTCAL0AOscillator Temperature Calibration Register A

Address
0x75
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0–

OSCTCAL0BOscillator Temperature Calibration Register B

Address
0x76
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0–

OSCCAL1Oscillator Calibration Register 32kHz

Address
0x77
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0–

PORTB I/O Port

PINBPort B Data register

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

DDRBData Direction Register, Port B

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

PORTBInput Pins, Port B

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

PUEBPull-up Enable Control Register

Address
0x62
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3PUEB3
  6. 2PUEB2
  7. 1PUEB1
  8. 0PUEB0

PORTCRPort Control Register

Address
0x64
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1BBMB
  8. 0–
1 field
FieldBitsWhat it does
BBMB1Break-Before-Make Mode Enable

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

DDRAData Direction Register, Port A

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

PUEAPull-up Enable Control Register

Address
0x63
Reset
0x00
Access
read/write
  1. 7PUEA7
  2. 6PUEA6
  3. 5PUEA5
  4. 4PUEA4
  5. 3PUEA3
  6. 2PUEA2
  7. 1PUEA1
  8. 0PUEA0

PORTCRPort Control Register

Address
0x64
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0BBMA
1 field
FieldBitsWhat it does
BBMA0Break-Before-Make Mode Enable

PHDEPort High Drive Enable Register

Address
0x6A
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1PHDEA1
  8. 0PHDEA0
1 field
FieldBitsWhat it does
PHDEA1:0PortA High Drive Enable

EEPROM EEPROM

EECREEPROM Control Register

Address
0x3C I/O 0x1C
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
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 Address Register Bytes

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

WDT Watchdog Timer

WDTCSRWatchdog Timer Control and Status Register

Address
0x41 I/O 0x21
Reset
0x00
Access
read/write
  1. 7WDIF
  2. 6WDIE
  3. 5WDP5
  4. 4–
  5. 3WDE
  6. 2WDP2
  7. 1WDP1
  8. 0WDP0
4 fields
FieldBitsWhat it does
WDIF7Watchdog Timer Interrupt Flag
WDIE6Watchdog Timer Interrupt Enable
WDP5,2,1,0Watchdog Timer Prescaler Bits
  • 0 Oscillator Cycles 512 (16 ms)
  • 1 Oscillator Cycles 1K (32 ms)
  • 2 Oscillator Cycles 2K (64 ms)
  • 3 Oscillator Cycles 4K (0.125 s)
  • 4 Oscillator Cycles 8K (0.25 s)
  • 5 Oscillator Cycles 16K (0.5 s)
  • 6 Oscillator Cycles 32K (1.0 s)
  • 7 Oscillator Cycles 64K (2.0 s)
  • 8 Oscillator Cycles 128K (4.0 s)
  • 9 Oscillator Cycles 256K (8.0 s)
WDE3Watch Dog Enable

TC0 Timer/Counter, 8-bit

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. 0PSR
2 fields
FieldBitsWhat it does
TSM7Timer/Counter Synchronization Mode
PSR0Prescaler Reset Timer/CounterN

TCCR0ATimer/Counter Control Register A

Address
0x50 I/O 0x30
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 Match Output A Mode bits
COM0B5:4Compare Match Output B Mode bits
WGM01:0Waveform Generation Mode bits

TCNT0Timer/Counter0

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–

TCCR0BTimer/Counter Control Register B

Address
0x53 I/O 0x33
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
WGM023Waveform Generation Mode bit 2
CS02:0Clock Select 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

OCR0ATimer/Counter0 Output Compare Register A

Address
0x56 I/O 0x36
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0–

TIFR0Timer/Counter0 Interrupt Flag Register

Address
0x58 I/O 0x38
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 B
OCF0A1Timer/Counter0 Output Compare Flag A
TOV00Timer/Counter0 Overflow Flag

TIMSK0Timer/Counter Interrupt Mask Register

Address
0x59 I/O 0x39
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

OCR0BTimer/Counter0 Output Compare Register B

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–

SPI Serial Peripheral Interface

REMAPRemap Port Pins

Address
0x65
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1SPIMAP
  8. 0–
1 field
FieldBitsWhat it does
SPIMAP1SPI Pin Mapping

SPDRSPI Data Register

Address
0xB0
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0–

SPSRSPI Status Register

Address
0xB1
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

SPCRSPI Control Register

Address
0xB2
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 fcl/4
  • 1 fcl/16
  • 2 fcl/64
  • 3 fcl/128

USART0 USART

REMAPRemap Port Pins

Address
0x65
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0U0MAP
1 field
FieldBitsWhat it does
U0MAP0USART0 Pin Mapping

UDR0USART I/O Data Register

Address
0x80
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0–

UBRR0USART Baud Rate Register Bytes

Address
0x81
Reset
0x0000
Access
read/write
Size
16-bit

UCSR0DUSART Control and Status Register D

Address
0x83
Reset
0x00
Access
read/write
  1. 7RXSIE0
  2. 6RXS0
  3. 5SFDE0
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0–
3 fields
FieldBitsWhat it does
RXSIE07USART RX Start Interrupt Enable
RXS06USART RX Start Flag
SFDE05USART RX Start Frame Detection Enable

UCSR0CUSART Control and Status Register C

Address
0x84
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

UCSR0BUSART Control and Status Register B

Address
0x85
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
0x86
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

TOCPM Timer/Counter Output Compare Pin

TOCPMCOETimer Output Compare Pin Mux Channel Output Enable

Address
0x66
Reset
0x00
Access
read/write
  1. 7TOCC7OE
  2. 6TOCC6OE
  3. 5TOCC5OE
  4. 4TOCC4OE
  5. 3TOCC3OE
  6. 2TOCC2OE
  7. 1TOCC1OE
  8. 0TOCC0OE
8 fields
FieldBitsWhat it does
TOCC7OE7Timer Output Compare Channel 7 Output Enable
TOCC6OE6Timer Output Compare Channel 6 Output Enable
TOCC5OE5Timer Output Compare Channel 5 Output Enable
TOCC4OE4Timer Output Compare Channel 4 Output Enable
TOCC3OE3Timer Output Compare Channel 3 Output Enable
TOCC2OE2Timer Output Compare Channel 2 Output Enable
TOCC1OE1Timer Output Compare Channel 1 Output Enable
TOCC0OE0Timer Output Compare Channel 0 Output Enable

TOCPMSA0Timer Output Compare Pin Mux Selection 0

Address
0x67
Reset
0x00
Access
read/write
  1. 7TOCC3S1
  2. 6TOCC3S0
  3. 5TOCC2S1
  4. 4TOCC2S0
  5. 3TOCC1S1
  6. 2TOCC1S0
  7. 1TOCC0S1
  8. 0TOCC0S0
4 fields
FieldBitsWhat it does
TOCC3S7:6Timer Output Compare Channel 3 Selection Bits
TOCC2S5:4Timer Output Compare Channel 2 Selection Bits
TOCC1S3:2Timer Output Compare Channel 1 Selection Bits
TOCC0S1:0Timer Output Compare Channel 0 Selection Bits

TOCPMSA1Timer Output Compare Pin Mux Selection 1

Address
0x68
Reset
0x00
Access
read/write
  1. 7TOCC7S1
  2. 6TOCC7S0
  3. 5TOCC6S1
  4. 4TOCC6S0
  5. 3TOCC5S1
  6. 2TOCC5S0
  7. 1TOCC4S1
  8. 0TOCC4S0
4 fields
FieldBitsWhat it does
TOCC7S7:6Timer Output Compare Channel 7 Selection Bits
TOCC6S5:4Timer Output Compare Channel 6 Selection Bits
TOCC5S3:2Timer Output Compare Channel 5 Selection Bits
TOCC4S1:0Timer Output Compare Channel 4 Selection Bits

USART1 USART

UDR1USART I/O Data Register

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

UBRR1USART Baud Rate Register Bytes

Address
0x91
Reset
0x0000
Access
read/write
Size
16-bit

UCSR1DUSART Control and Status Register D

Address
0x93
Reset
0x00
Access
read/write
  1. 7RXSIE1
  2. 6RXS1
  3. 5SFDE1
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0–
3 fields
FieldBitsWhat it does
RXSIE17USART RX Start Interrupt Enable
RXS16USART RX Start Flag
SFDE15USART RX Start Frame Detection Enable

UCSR1CUSART Control and Status Register C

Address
0x94
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

UCSR1BUSART Control and Status Register B

Address
0x95
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
0x96
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

TWI Two Wire Serial Interface

TWSDTWI Slave Data Register

Address
0xA0
Reset
0x00
Access
read/write
  1. 7TWSD7
  2. 6TWSD6
  3. 5TWSD5
  4. 4TWSD4
  5. 3TWSD3
  6. 2TWSD2
  7. 1TWSD1
  8. 0TWSD0
1 field
FieldBitsWhat it does
TWSD7:0TWI slave data bit

TWSAMTWI Slave Address Mask Register

Address
0xA1
Reset
0x00
Access
read/write
  1. 7TWSAM6
  2. 6TWSAM5
  3. 5TWSAM4
  4. 4TWSAM3
  5. 3TWSAM2
  6. 2TWSAM1
  7. 1TWSAM0
  8. 0TWAE
2 fields
FieldBitsWhat it does
TWSAM7:1TWI Address Mask Bits
TWAE0TWI Address Enable

TWSATWI Slave Address Register

Address
0xA2
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3–
  6. 2–
  7. 1–
  8. 0–

TWSSRATWI Slave Status Register A

Address
0xA3
Reset
0x00
Access
read/write
  1. 7TWDIF
  2. 6TWASIF
  3. 5TWCH
  4. 4TWRA
  5. 3TWC
  6. 2TWBE
  7. 1TWDIR
  8. 0TWAS
8 fields
FieldBitsWhat it does
TWDIF7TWI Data Interrupt Flag.
TWASIF6TWI Address/Stop Interrupt Flag
TWCH5TWI Clock Hold
TWRA4TWI Receive Acknowledge
TWC3TWI Collision
TWBE2TWI Bus Error
TWDIR1TWI Read/Write Direction
TWAS0TWI Address or Stop

TWSCRBTWI Slave Control Register B

Address
0xA4
Reset
0x00
Access
read/write
  1. 7–
  2. 6–
  3. 5–
  4. 4–
  5. 3TWHNM
  6. 2TWAA
  7. 1TWCMD1
  8. 0TWCMD0
3 fields
FieldBitsWhat it does
TWHNM3TWI High Noise Mode
TWAA2TWI Acknowledge Action
TWCMD1:0

TWSCRATWI Slave Control Register A

Address
0xA5
Reset
0x00
Access
read/write
  1. 7TWSHE
  2. 6–
  3. 5TWDIE
  4. 4TWASIE
  5. 3TWEN
  6. 2TWSIE
  7. 1TWPME
  8. 0TWSME
7 fields
FieldBitsWhat it does
TWSHE7TWI SDA Hold Time Enable
TWDIE5TWI Data Interrupt Enable
TWASIE4TWI Address/Stop Interrupt Enable
TWEN3Two-Wire Interface Enable
TWSIE2TWI Stop Interrupt Enable
TWPME1TWI Promiscuous Mode Enable
TWSME0TWI Smart Mode Enable