Basic Embedded Systems
Embedded systems are computer systems designed for a specific function inside a larger device.
Examples:
- washing machine controller,
- car ABS system,
- microwave oven,
- smart watch,
- printer controller.
Embedded system characteristics
- task-specific,
- resource constrained,
- often real-time,
- reliable,
- low power,
- interacts with hardware sensors/actuators.
Microprocessor vs Microcontroller
| Microprocessor | Microcontroller |
|---|---|
| CPU only | CPU + memory + I/O on one chip |
| Needs external RAM/ROM/peripherals | Built-in peripherals |
| Used in PCs/general systems | Used in embedded systems |
| Higher processing capability | Lower cost/power |
Sensor and actuator
Sensor: converts physical quantity to electrical signal.
Examples: temperature sensor, pressure sensor.
Actuator: converts electrical signal to physical action.
Examples: motor, relay, buzzer.
ADC and DAC
ADC: Analog to Digital Converter.
Used when sensor signal is analog but microcontroller processes digital values.
DAC: Digital to Analog Converter.
Used when digital output must become analog voltage/current.
Interrupt
Interrupt is a signal that temporarily stops normal program execution and runs an Interrupt Service Routine.
Advantages:
- fast response,
- avoids constant checking.
ISR:
Interrupt Service Routine, the function executed when interrupt occurs.
Polling vs Interrupt
| Polling | Interrupt |
|---|---|
| CPU repeatedly checks status | Device notifies CPU |
| Simple | More efficient |
| Wastes CPU time | Better for real-time events |
Timer
Timer generates accurate delays or periodic events.
Uses:
- delays,
- PWM generation,
- event counting,
- scheduling.
Watchdog timer
Watchdog resets system if software hangs.
Method:
- Program must periodically reset/kick watchdog.
- If not, watchdog assumes failure and resets device.
RTOS
RTOS = Real-Time Operating System.
It gives deterministic response within deadlines.
Key terms:
- task/thread,
- priority,
- scheduler,
- latency,
- deadline,
- semaphore,
- mutex.
Hard real-time:
- Missing deadline is system failure.
- Example: airbag.
Soft real-time:
- Missing deadline degrades quality.
- Example: video streaming.
Communication protocols
UART
- asynchronous serial communication,
- uses TX/RX lines,
- no clock line,
- common in debugging and modules.
SPI
- synchronous,
- fast,
- master-slave,
- uses MOSI, MISO, SCLK, SS.
I2C
- synchronous,
- two wires: SDA and SCL,
- supports multiple devices using addresses.
Memory in embedded systems
- ROM/Flash: stores program permanently.
- RAM: temporary runtime data.
- EEPROM: non-volatile small data storage.
Common MCQ traps
- Microcontroller includes CPU, memory, and peripherals.
- Interrupt is event-driven.
- Polling wastes CPU cycles.
- ADC converts analog to digital, not digital to analog.
- Watchdog improves reliability by resetting stuck systems.