Microcontroller architecture and interfacing: the structure of a microcontroller (CPU, memory, ports), digital input and output ports, interfacing switches, sensors and output devices, and the on-chip ADC.

What this dot point is asking

The microcontroller is the programmable processing block at the heart of most modern systems, and Component 2 expects you to understand its structure and how the outside world connects to it. WJEC expects you to describe the architecture (CPU, memory, ports), explain digital input and output ports, interface switches, sensors and output devices correctly, and use the on-chip ADC. The interfacing question (pull-up resistors, transistor drivers, flyback diodes) is reliable, high-mark exam content.

The answer

The architecture of a microcontroller

Digital input and output ports

Each port pin is set in software to be an input (the program reads its logic level) or an output (the program drives it high or low). An output pin can source or sink only a small current, so larger loads need interfacing.

Interfacing inputs

Interfacing outputs and reading analogue sensors

Examples in context

Example 1. A digital thermostat

A thermistor divider feeds an analogue input; the microcontroller reads the temperature through its ADC, compares it with a set point in software, and switches a heater through a transistor and relay. The architecture (ADC input, program logic, driven output) is the whole system in one chip plus interfacing.

Example 2. A keypad door lock

Push switches with pull-up resistors connect to digital input pins; the microcontroller reads the keys, checks the code, and drives a solenoid through a transistor to release the lock. The pull-ups give clean reads, and the transistor handles the solenoid current.

Example 3. Replacing discrete logic

A task once built from many logic chips, counters and timers can be done by one microcontroller running a program, with only interfacing components outside. This flexibility, reprogramming rather than rewiring, is why microcontrollers dominate Component 2 system designs.

Try this

Q1. State why a switch connected to a microcontroller input needs a pull-up (or pull-down) resistor. [2 marks]

• Cue. So the pin reads a definite logic level when the switch is open; without it the input floats and reads unpredictably.

Q2. Explain why an on-chip ADC is useful in a microcontroller. [2 marks]

• Cue. Many sensors give analogue voltages but the microcontroller is digital; the on-chip ADC lets it read those analogue signals directly, without an external converter.