Input/Output (IO)

IO is a big part of what makes Meadow powerful. Meadow boards expose a wide variety of ways to control and interact with external peripherals and hardware via Input/Output (IO) ports.

Pins + Connectors

IO ports are exposed physically on the board via pins and other connectors. These physical connections can be accessed from your application code to read sensors, listen to button presses, light LEDs, drive motors, communicate with other systems, and lots more.

Many of the pins on a Meadow board are multifunction, which means that they can serve as different types of IO, depending on how they're configured in code.

Types of IO

Meadow IO ports are generally divided into two categories: Digital and Analog. There is also another type of IO, Power, which is discussed in the power guide.

Digital and analog refer to the type of electrical signal used; either HIGH/LOW for digital, or a range of voltages for analog, and they're used for different things.

Digital IO

Digital IO is often referred to as General Purpose, Input/Output or GPIO.

Digital ports can be set to be HIGH (powered at 3.3V), or LOW (grounded at 0V) which correspond to digital 1 and 0, respectively. They can also be setup as input ports which can read signal inputs to know if they're HIGH, LOW, and can also raise notifications on change, via interrupts.

For more information, see the Digital IO guide.

Digital Communications Protocols

Additionally, the digital ports have built-in support for a host of different types of common digital communication protocols including:

• I2C (Inter Integrated Circuit)
• SPI (Serial Peripheral Interface)
• UART (Serial)

Pulse-Width-Modulation (PWM)

Additionally, digital output ports can be used to generate a Pulse-Width-Modulation (PWM) signal, which approximates an intermediate voltage between LOW or HIGH by switching between ON and OFF very quickly. PWM signals are frequently used to control the brightness of LEDs, as well as serve as the control signal for precision motors such as servos and stepper motors.

For more information, see the PWM guide.

Analog IO

Analog ports can operate at a range of voltages between 0V and 3.3V, which is especially useful when reading analog sensors that supply their data as a voltage reading, rather than a digital signal. For instance an analog temperature sensor that is able to detect temperatures from 0ºC to 100ºC might output a voltage of 1.6V (halfway between 0V and 3.3V) for 50º.

For more information, see the Analog IO guide.

I/O Power Tolerance

Important:

Both the digital and analog I/O on the Meadow F7 board nominally operate at a range of 0V to 3.3V. However, when they are configured for digital operation, they are 5V tolerant; meaning that they can accept input voltages up to 5V. When they are configured for analog operation, they are only 3.3V tolerant, and any input voltages higher than that, may burn out that I/O, and or damage the chip.

For reading analog voltages higher than 3.3V, see the analog I/O guide

F7 Feather IO Pinout

GPIO ports are available via pins (as well as the onboard LED) on the Meadow F7 Feather, and many of these pins are actually overloaded to support multiple functions, as shown in the below illustrations.

Meadow F7v2 Feather Pinout

Meadow F7v1 Feather Pinout

The function that they serve depends on how they are configured when a port is instantiated on one of the pins. For instance, pin D00 can be configured to be used a digital input or output, or as the RX (receive) half of a Serial UART port available as "COM4".

Pins, Ports, and ChannelInfos

When working with IO in Meadow, there are three different terms/concepts to be aware of:

• IPin - Represents a physical connection point on a device, such as pin D01.
• IPort - Represents the underlying IO feature that allows communication, such as a Meadow.Hardware.DigitalInputPort which reads digital input signals on a particular pin.
• IChannelInfo - Describes the capabilities of a particular pin or port, for instance, whether or not a pin supports digital interrupts (a notification when the state changes).

IIOController

A device that supports IO (such as the F7 Feather device itself, or an external IO Expander) is represented by an IIOController, which exposes a Pins collection of IPin objects.

IO Devices are self describing with a mapping of Device > Pins > Channels. For instance, the following Meadow sample code enumerates all the pins and what type of IO is possible for each pin:

foreach(var pin in Device.Pins.AllPins) {
   Console.WriteLine("Found pin: " + pin.Name);
   foreach (var channel in pin.SupportedChannels) {
            Console.WriteLine("Contains a " + channel.GetType()
            + "channel called: " + channel.Name + ".");
   }
}

Here's an excerpt from the output the above code returns:

Found pin: A05
Contains a Meadow.Hardware.DigitalChannelInfochannel called: PC1.
Contains a Meadow.Hardware.AnalogChannelInfochannel called: ADC1_IN11.

Found pin: D00
Contains a Meadow.Hardware.DigitalChannelInfochannel called: PI9.
Contains a Meadow.Hardware.UartChannelInfochannel called: UART4_RX.

Found pin: D01
Contains a Meadow.Hardware.DigitalChannelInfochannel called: PH13.
Contains a Meadow.Hardware.PwmChannelInfochannel called: TIM8_CH1N.
Contains a Meadow.Hardware.UartChannelInfochannel called: UART4_TX.

With these IChannelInfo objects, the IO is also self-documenting, and you can see what kind of ports are available from each pin without having to refer to the IO pinout diagram.

Creating Ports

When interacting with peripherals, the actual control and interaction happens via IPort objects, which are typically created via the device from one or more pins:

IDigitalOutputPort redLED = Device.CreateDigitalOutputPort(Device.Pins.OnboardLedRed);

Meadow F7 Feather Pinout Table

The following table lists all the accessible pins on the Meadow F7 Feather dev board and their functions:

Meadow Pin Name	MCU Pin Name	Digital Channel	Analog Channel	PWM Timer Channel	Interrupt Group
A00	PA4	PA4	AC1_IN4		4
A01	PA5	PA5	ADC1_IN5		5
A02	PA3	PA3	ADC1_IN3		3
A03	PA7	PA7	ADC1_IN7		7
A04	PC0	PC0	ADC1_IN10		0
A05	PC1	PC1	ADC1_IN11		1
SCK	PC10	PC10
MOSI	PB5	PB5			5
MISO	PC11	PC11			11
D00	PI9	PI9			9
D01	PH13	PH13
D02	PC6	PC6		1	6
D03	PB8	PB8		3	8
D04	PB9	PB9		4	9
D05	PC7	PC7		2	7
D06	PB0	PB0	ADC1_IN8	3	0
D07	PB7	PB7		2	7
D08	PB6	PB6		1	6
D09	PB1	PB1	ADC1_IN9	4	1
D10	PH10	PH10		1
D11	PC9	PC9		4	9
D12	PB14	PB14		1	14
D13	PB15	PB15		2	15
D14	PG3	PG3			3
D15	PE3	PE3			3
OnboardLedRed	PA2	PA2		3
OnboardLedGreen	PA1	PA1		2
OnboardLedBlue	PA0	PA0		1

Meadow F7v2 Feather Pinout Table

Meadow Pin Name	MCU Pin Name	Digital Channel	Analog Channel	PWM Timer Channel	Interrupt Group
A00	PA4	PA4	ADC1_IN4		4
A01	PA5	PA5	ADC1_IN5		5
A02	PA3	PA3	ADC1_IN3		3
A03	PB0	PB0	ADC1_IN8		0
A04	PB1	PB1	ADC1_IN9		1
A05	PC0	PC0	ADC1_IN10		0
SCK	PC10	PC10
COPI	PB5	PB5			5
CIPO	PC11	PC11			11
D00	PI9	PI9			9
D01	PH13	PH13			13
D02	PH10	PH10		1
D03	PB8	PB8		3	8
D04	PB9	PB9		4	9
D05	PB4	PB4		1	4
D06	PB13	PB13		1	13
D07	PB7	PB7		2	7
D08	PB6	PB6		1	6
D09	PC6	PC6		1	6
D10	PC7	PC7		2	7
D11	PC9	PC9		4
D12	PB14	PB14		1	14
D13	PB15	PB15		2	15
D14	PB12	PB12
D15	PG12	PB12
OnboardLedRed	PA2	PA2		3	2
OnboardLedGreen	PA1	PA1		2	1
OnboardLedBlue	PA0	PA0		1	0

Meadow.Foundation

When building Meadow applications, most of the time, you'll use high-level peripheral drivers via Meadow.Foundation instead of interacting with ports directly, as we'll explore in the next section.

Next - Meadow.Foundation