What is inside a microcontroller, and how does it connect to the inputs and outputs of a system?
Microcontroller architecture: the CPU, memory and input/output ports, digital input and output pins, pull-up and pull-down resistors, and the analogue-to-digital converter and PWM peripherals.
An Eduqas A-Level Electronics answer on microcontroller architecture and interfacing: the CPU, memory and input/output ports, digital input and output pins with pull-up and pull-down resistors, and the built-in peripherals (analogue-to-digital converter, PWM, timers) that connect the microcontroller to the real world.
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What this dot point is asking
Eduqas wants you to describe a microcontroller's architecture (CPU, memory, input/output ports), digital input and output pins, pull-up and pull-down resistors, and the built-in peripherals (ADC, PWM, timers). The microcontroller is the programmable brain that ties a modern electronic system together.
The answer
Microcontroller architecture
Digital input and output pins
Pull-up and pull-down resistors
Built-in peripherals
Examples in context
The microcontroller is the heart of almost every modern electronic product, from a washing machine to a toy to a sensor node. Its ADC reads the sensing circuits from earlier modules, its PWM drives the motors and LEDs through the switching devices, and its digital pins read switches (with pull resistors) and drive logic. Eduqas requires you to program one in assembly language for the non-exam assessment, so understanding the ports and peripherals here is the foundation for the programming topic that follows.
Try this
Q1. Name the three main internal parts of a microcontroller. [3 marks]
- Cue. The CPU (processor), memory (program memory and RAM), and input/output ports.
Q2. State what happens to a microcontroller input pin left floating. [1 mark]
- Cue. It picks up noise and reads a random, undefined logic level.
Q3. Name the peripheral that lets a microcontroller read an analogue sensor voltage. [1 mark]
- Cue. The analogue-to-digital converter (ADC).
Exam-style practice questions
Practice questions written in the style of WJEC Eduqas exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Eduqas 20215 marksA push switch is connected to a microcontroller input pin. Explain why a pull-up (or pull-down) resistor is needed, and describe the logic level the pin reads when the switch is open and when it is closed for a pull-up arrangement.Show worked answer →
Why a resistor is needed (up to 3 marks): without it, when the switch is open the input pin is left floating (connected to nothing), so it picks up electrical noise and reads an unpredictable, randomly changing logic level. A pull-up (or pull-down) resistor ties the pin to a defined voltage when the switch is open, giving a reliable logic level.
Pull-up behaviour (up to 2 marks): a pull-up resistor connects the pin to the positive supply, and the switch connects the pin to . When the switch is open, the resistor pulls the pin high (logic ). When the switch is closed, the pin is connected directly to , so it reads low (logic ).
Markers reward the floating-pin problem (noise, undefined level), the resistor setting a defined level, and the pull-up giving high when open and low when closed.
Eduqas 20225 marksDescribe the main internal parts of a microcontroller, and name two built-in peripherals that let it interface with analogue and high-power devices.Show worked answer →
Internal parts (up to 3 marks): a microcontroller contains a CPU (processor) that executes the program, memory (program memory, often flash, holding the code, and RAM holding data), and input/output ports through which it reads inputs and drives outputs. A clock (oscillator) steps the CPU, and a bus connects the parts. It is a complete computer on one chip.
Peripherals (up to 2 marks): two valid examples are an analogue-to-digital converter (ADC) to read an analogue sensor voltage, and a PWM (pulse-width modulation) output to control the power to a motor, LED or heater. (Timers, serial communication interfaces and comparators are also acceptable.)
Markers reward the CPU, memory and I/O ports (a computer on a chip) and two valid peripherals such as the ADC and PWM.
Related dot points
- Assembly language programming: instructions and registers, reading inputs and writing outputs, branching and loops, delays, and the program development cycle (flowchart, code, assemble, test).
An Eduqas A-Level Electronics answer on assembly language programming: instructions and registers, reading input pins and writing to output pins, branching and looping for decisions and repetition, generating delays, and the flowchart-code-assemble-test development cycle required for the non-exam assessment.
- Interfacing a microcontroller: input interfacing (signal conditioning, switch debouncing, the ADC), output interfacing (transistor and MOSFET drivers, relays, motor control with PWM and an H-bridge), and the closed-loop control system.
An Eduqas A-Level Electronics answer on interfacing a microcontroller: conditioning and reading sensor inputs (including switch debouncing and the ADC), driving outputs safely through transistor, MOSFET and relay drivers, controlling motor speed and direction with PWM and an H-bridge, and the structure of a closed-loop control system.
- Analogue-to-digital conversion: sampling, quantisation and resolution, the sampling theorem and aliasing, quantisation error, and the trade-off between resolution and data rate.
An Eduqas A-Level Electronics answer on analogue-to-digital conversion: sampling a continuous signal, quantisation and resolution, the Nyquist sampling theorem and aliasing, quantisation error, and the trade-off between resolution, sampling rate and the data rate produced.
- Number systems: binary, denary and hexadecimal conversion, binary addition, two's complement for signed numbers, and binary-coded decimal.
An Eduqas A-Level Electronics answer on number systems: converting between binary, denary and hexadecimal, binary addition with carries, two's complement representation of signed numbers and subtraction by addition, and binary-coded decimal for displays.
Sources & how we know this
- Eduqas GCE AS/A Level Electronics specification (A410QS) — WJEC Eduqas (2017)