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3.8. Pin assignments

The table below lists the most important pin assignments for the ATmega32U4 on the Romi 32U4 Control Board. This table is helpful if you want to add your own electronics to the Romi 32U4, write your own low-level code for interfacing with the hardware, or just want to understand better how the Romi 32U4 works. Each row represents a physical pin on the ATmega32U4.

The “ATmega32U4 pin name” column shows the official name of the pin according to the ATmega32U4 datasheet.

The “Arduino pin names” column lists the names provided by the Arduino environment for the pin. These names can generally be used as arguments to any function that takes a pin number. However, there are some exceptions. For example, passing the number 4 to analogRead actually reads pin A4, not pin 4. Also, due to hardware limitations, some functions only work on a limited set of pins.

The “Romi 32U4 functions” column documents what the pin is used for on the Romi 32U4 Control Board. Many pins can serve multiple purposes concurrently by switching modes. For example, PB0 can read the state of button C when it is an input, and it can control the red LED and serve as an LCD data line when it is an output.

The “Note/alternate functions” column documents other features of the pin, although some of those features might be impractical to use.

ATmega32U4
pin name
Arduino
pin names
Romi 32U4 Control Board
functions
Notes/alternate functions
PB7 11 LCD control line (E) Timer0 PWM output A (OC0A)
Timer1 PWM output C (OC1C)
UART flow control (RTS)
Pin-change interrupt (PCINT7)
PD4 4, A6, 24 LCD control line (RS) Analog input (ADC8)
Timer1 input capture pin (ICP1)
PB3 14, MISO User pushbutton A
LCD data line DB4
SPI Master Input/Slave Output (MISO)
Pin-change interrupt (PCINT3)
ISP programming line (PDO)
PB0 17, LED_BUILTIN_RX, SS Red LED (RX)
User pushbutton C
LCD data line DB5
SPI slave select (SS)
Pin-change interrupt (PCINT0)
PC7 13, LED_BUILTIN Yellow LED
LCD data line DB6
Timer4 PWM output A (OC4A)
Timer3 input capture pin (ICP3)
Divided system clock output (CLKO)
PD5 30, LED_BUILTIN_TX Green LED (TX)
User pushbutton B
LCD data line DB7
UART external clock (XCK1)
UART flow control (CTS)
PD7 6, A7, 25 Buzzer PWM Analog input (ADC10)
Timer4 PWM output D (OC4D)
Timer0 counter source (T0)
PF6 A1, 19 Battery level input (VIN/3) Analog input (ADC6)
JTAG test data out (TDO)
PB6 10, A10, 28 Left Motor PWM Analog input (ADC13)
Timer1 PWM output B (OC1B)
Timer4 PWM output B (OC4B)
Pin-change interrupt (PCINT6)
PB2 16, MOSI Left motor direction SPI Master Output/Slave Input (MOSI)
Pin-change interrupt (PCINT2)
ISP programming line (PDI)
PB5 9, A9, 27 Right motor PWM Analog input (ADC12)
Timer1 PWM output A (OC1A)
Timer4 PWM output B (OC4B)
Pin-change interrupt (PCINT5)
PB1 15, SCK Right motor direction SPI Clock (SCK)
Pin-change interrupt (PCINT1)
ISP programming line (SCK)
PB4 8, A8, 26 Left encoder XORed input Analog input (ADC11)
Pin-change interrupt (PCINT4)
PE2 - Left encoder input Hardware bootloader select (HWB)
PE6 7 Right encoder XORed input Analog comparator negative input (AIN0)
External interrupt source (INT6)
PF0 A5, 23 Right encoder input Analog input (ADC0)
PD0 3, SCL I²C clock for Raspberry Pi communication and inertial sensors Timer0 PWM output B (OC0B)
External interrupt source (INT0)
PD1 2, SDA I²C data for Raspberry Pi communication and inertial sensors External interrupt source (INT1)
PD2 0 Free I/O UART receive pin (RXD1)
External interrupt source (INT2)
PD3 1 Free I/O UART transmit pin (TXD1)
External interrupt source (INT3)
PC6 5 Free I/O Timer3 PWM output A (OC3A)
Timer4 PWM output A (OC4A)
PD6 12, A11, 29 Free I/O Analog input (ADC9)
Timer4 PWM output D (OC4D)
Timer1 counter source (T1)
PF7 A0, 18 Free I/O Analog input (ADC7)
JTAG test data in (TDI)
PF5 A2, 20 Free I/O Analog input (ADC5)
JTAG test mode select (TMS)
PF4 A3, 21 Free I/O Analog input (ADC4)
JTAG test clock (TCK)
PF1 A4, 22 Free I/O Analog input (ADC1)
RESET - Reset pushbutton internally pulled high, active low
AREF - - Analog reference

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