General-purpose input/output (GPIO)

The most basic functionality that can be achieved with any microcontroller is the possibility to control signals on specific pins of the integrated circuit. The microcontroller can turn a digital output on or off, which corresponds to a reference voltage to be applied to the pin when the value assigned to it is 1, and zero volts when the value is 0. In the same way, a pin can be used to detect a 1 or a 0 when the pin is configured as input. The software will read the digital value “1” when the voltage applied to it is higher than a certain threshold.

ADC and DAC

Some chips have onboard ADC controllers, which are capable of sensing the voltage that is applied to the pin and sampling it. This is often used to acquire measurements from input peripherals providing a variable voltage as output. The embedded software will be able to read the voltage, with an accuracy that depends on the predefined range.

A DAC controller is the inverse of an ADC controller, transforming a value on a microcontroller register into the corresponding voltage.

Timers and PWM

Microcontrollers may offer diverse ways to measure time. Often, there is at least one interface based on a countdown timer that can trigger an interrupt and automatically reset upon expiry.

GPIO pins configured as output can be programmed to output a square wave with a preconfigured frequency and duty cycle. This is called pulse-wave modulation (PWM) and has several uses, from controlling output peripherals to dimming an LED or even playing an audible sound through a speaker.

More details about GPIO, interrupt timers, and watchdogs will be explored in Chapter 6, General-Purpose Peripherals.