GPIO

The Maple features 38 ready-to-use general purpose input/output (GPIO) pins for digital input/output, numbered D0 through D37. These numbers correspond to the numeric values next to each header on the Maple silkscreen.

Many of these pins may additionally be used for special features or peripheral functions. This page documents those capabilities, by pin.

The current and voltage limitations have been copied over from the STM32 datasheet (see the Recommended Reading for a link). In particular, a number of GPIO pins are 5V tolerant (which means that applying 5 volts to a pin and reading it as input or allowing it to drain to ground will not damage that pin), while some are not.

Pin Mapping Mega Table

This table shows the available functionality on every GPIO pin, by peripheral type. The “STM32” column refers to the port and number that the header is connected to on the microcontroller. The “5V?” column documents whether or not the pin is 5 volt tolerant (see above).

Pin	STM32	ADC	Timer	I2C	UART	SPI	5v?
D0	PA3	ADC3	TIM2_CH4		USART2_RX		No
D1	PA2	ADC2	TIM2_CH3		USART2_TX		No
D2	PA0	ADC0	TIM2_CH1_ETR		USART2_CTS		No
D3	PA1	ADC1	TIM2_CH2		USART2_RTS		No
D4	PB5			ISC1_SMBA			No
D5	PB6		TIM4_CH1	I2C1_SCL			Yes
D6	PA8		TIM1_CH1		USART1_CK		Yes
D7	PA9		TIM1_CH2		USART1_TX		Yes
D8	PA10		TIM1_CH3		USART1_RX		Yes
D9	PB7		TIM4_CH2	I2C1_SDA			Yes
D10	PA4	ADC4			USART2_CK	SPI1_NSS	No
D11	PA7	ADC7	TIM3_CH2			SPI1_MOSI	No
D12	PA6	ADC6	TIM3_CH1			SPI1_MISO	No
D13	PA5	ADC5				SPI1_SCK	No
D14	PB8		TIM4_CH3				Yes
D15	PC0	ADC10					No
D16	PC1	ADC11					No
D17	PC2	ADC12					No
D18	PC3	ADC13					No
D19	PC4	ADC14					No
D20	PC5	ADC15					No
D21	PC13						No
D22	PC14						No
D23	PC15						No
D24	PB9		TIM4_CH4				Yes
D25	PD2		TIM3_ETR				Yes
D26	PC10						Yes
D27	PB0	ADC8	TIM3_CH3				No
D28	PB1	ADC9	TIM3_CH4				No
D29	PB10			I2C2_SCL	USART3_TX		Yes
D30	PB11			I2C2_SDA	USART3_RX		Yes
D31	PB12		TIM1_BKIN	I2C2_SMBAL	USART3_CK	SPI2_NSS	Yes
D32	PB13		TIM1_CH1N		USART3_CTS	SPI2_SCK	Yes
D33	PB14		TIM1_CH2N		USART3_RTS	SPI2_MISO	Yes
D34	PB15		TIM1_CH3N			SPI2_MOSI	Yes
D35	PC6						Yes
D36	PC7						Yes
D37	PC8						Yes

GPIO Modes

WiringPinMode enum

Specifies a GPIO pin behavior.

Each of the GPIO pins on a Maple board may be configured using pinMode() to behave in a number of ways: as a digital output pin, or as an analog input pin, etc., depending on the particular pin.

This enum specifies the complete set of possible configurations; not every pin can have all of these modes. For example, on the Maple, pin 15 may be configured as INPUT_ANALOG, but not as PWM. See your device’s silkscreen and and the GPIO documentation for more information.

See

pinMode()

Values:

• OUTPUT -

  Basic digital output: when the pin is HIGH, the voltage is held at +3.3v (Vcc) and when it is LOW, it is pulled down to ground.

• OUTPUT_OPEN_DRAIN -

  In open drain mode, the pin indicates “low” by accepting current flow to ground and “high” by providing increased impedance.

  An example use would be to connect a pin to a bus line (which is pulled up to a positive voltage by a separate supply through a large resistor). When the pin is high, not much current flows through to ground and the line stays at positive voltage; when the pin is low the bus “drains” to ground with a small amount of current constantly flowing through the large resistor from the external supply. In this mode no current is ever actually /sourced/ from the pin.

• INPUT -

  Basic digital input.

  The pin voltage is sampled; when it is closer to 3.3v (Vcc) the pin status is high, and when it is closer to 0v (ground) it is low. If no external circuit is pulling the pin voltage to high or low, it will tend to randomly oscillate and be very sensitive to noise (e.g., a breath of air across the pin might cause the state to flip).

• INPUT_ANALOG -

  This is a special mode for when the pin will be used for analog (not digital) reads.

  Enables ADC conversion to be performed on the voltage at the pin.

• INPUT_PULLUP -

  The state of the pin in this mode is reported the same way as with INPUT, but the pin voltage is gently “pulled up” towards +3.3v.

  This means the state will be high unless an external device is specifically pulling the pin down to ground, in which case the “gentle” pull up will not affect the state of the input.

• INPUT_PULLDOWN -

  The state of the pin in this mode is reported the same way as with INPUT, but the pin voltage is gently “pulled down” towards 0v.

  This means the state will be low unless an external device is specifically pulling the pin up to 3.3v, in which case the “gentle” pull down will not affect the state of the input.

• INPUT_FLOATING -

  Synonym for INPUT.

• PWM -

  This is a special mode for when the pin will be used for PWM output (a special case of digital output).

• PWM_OPEN_DRAIN -

  Like PWM, except that instead of alternating cycles of LOW and HIGH, the voltage on the pin consists of alternating cycles of LOW and floating (disconnected).

Function Reference

• pinMode()
• digitalRead()
• digitalWrite()
• analogRead()
• pwmWrite() (Maple’s equivalent to analogWrite(); see the analogWrite() reference for differences from the Arduino version).

Recommended Reading

STMicro documentation for STM32F103RB microcontroller:

• Datasheet (pdf)
• Reference Manual (pdf)