embedded-programming/LED Blink Input Output/GPIO-notes-pins.md

Digital INPUT OUTPUT

There are three registers which initialize Digital INPUT and DIGITAL OUTPUT port:

1. DDRB
2. DDRC
3. DDRD

Each pin is 1 bit of DDRx.

Here P means Port
Example: PC → Port C

Microcontroller pins are grouped as:

1. PORTB → PB0–PB7
2. PORTC → PC0–PC6
3. PORTD → PD0–PD7

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Important

• In Arduino Uno, PC7 does not exist
  → PORTC is only PC0–PC6

• PB6 and PB7 are used by 16MHz crystal
  → DO NOT USE

• PC6 is RESET pin
  → DO NOT USE as GPIO
  → can reset system → can be used but condition is if reset is disabled.

• PD0 and PD1 are Serial pins (RX TX)
  → used for USB upload and debugging
  → DO NOT USE during development

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SPI (just remember)

• PB3 → MOSI
• PB4 → MISO
• PB5 → SCK

→ used for SPI and programming
→ can be used as GPIO but avoid if SPI used
→ PB5 has onboard LED

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I2C (just remember)

• PC4 → SDA
• PC5 → SCL

→ used for I2C communication

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Safe pins for Digital I/O

• PORTD → PD2–PD7
• PORTB → PB0–PB2 (PB3–PB5 usable but SPI)
• PORTC → PC0–PC5 (PC4 PC5 shared with I2C)

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Use with care

• PB3 PB4 PB5 → SPI pins
• PC4 PC5 → I2C pins

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Final

Best pins to use:

PD2–PD7
PB0–PB2
PC0–PC5

Avoid:

PB6 PB7 → crystal
PC6 → reset
PD0 PD1 → serial