MICROCONTROLLER DIGI NOTES by ELECTRICAL ZINDAGI
Table of Contents
Microcontroller Essentials — Quick, exam-focused one-liners
Microcontroller = CPU + Memory + I/O on single chip — remember: "C-MIO" (Compact Microcontroller In One).
Harvard vs Von-Neumann: Harvard has separate code/data buses — faster for DMA and peripherals.
RISC vs CISC: RISC uses fewer cycles per instruction — think "Reduced steps, faster loop" for time-critical tasks.
GPIO direction: Configure DDRx as 1 for output, 0 for input — trick: DDR = Data Direction Register.
Debounce switches: use 10–20 ms software delay or RC filter — exam trick: "Cap + resistor = clean click".
Analog readings require ADC; choose reference carefully — internal Vref gives stability, external for accuracy.
PWM duty cycle controls average voltage — use low-pass filter to convert PWM to analog voltage for motors.
I2C basics: two wires (SDA, SCL), address 7-bit or 10-bit — remember: "Pull-ups are mandatory".
SPI uses MOSI, MISO, SCK, SS — full-duplex high-speed; pick SPI for display and flash memory interfaces.
UART framing: start bit, data bits, optional parity, stop bits — common format 8-N-1 (8 data, no parity, 1 stop).
Interrupts save CPU cycles — use ISRs for external events; keep ISRs short to avoid priority inversion.
Watchdog timer resets MCU if stuck — enable in safety-critical designs; test by intentionally triggering reset during lab checks.
Timers count clock ticks — Timer prescalers trade off range vs resolution. Trick: prescale to fit expected time window.
Bootloader allows firmware update over serial — useful during field updates; keep bootloader small and protected.
Brown-out detection prevents unpredictable operation during low supply voltage — enable to protect flash writes.
EEPROM vs Flash: EEPROM supports byte writes; flash often needs page erase — exam often asks difference in erase/write granularity.
GPIO pull-ups: use internal pull-up for buttons to ground; external if you need stronger current or precise levels.
Use DMA for large, repeated data transfers (like ADC streaming) — frees CPU and reduces jitter for real-time tasks.
Power modes: sleep, standby, deep-sleep — choose lowest power that still allows required wake sources to save battery life.
Clock sources: crystal = accurate, internal RC = cheaper but drifts. For serial comms use crystal or calibrated internal clock.
Pin multiplexing: peripherals share pins — check datasheet and remap carefully to avoid conflicts.
Level shifting: use MOSFET-based or resistor divider + buffer when interfacing 5V peripherals to 3.3V MCU pins.
Serial boot vs OTA: Over-the-air needs secure update process; exams ask about integrity (use checksums/CRC).
ADC sampling rate: input source impedance matters — add small capacitor at ADC pin to reduce sampling error for high-res ADCs.
GPIO current limits: never exceed per-pin and total port currents; use external driver for motors and relays.
Debouncing trick: sample input every 5ms for 3 consecutive reads before accepting state change — simple and effective.
Use CRC16 for blocks of firmware to validate correctness after transfer — exam often asks about simple integrity checks.
Assembler vs C: learn basic assembly for understanding compiler output and timing-critical loops — exam q's often from both.
Interrupt priority: nested vectored interrupt controller (NVIC) orders ISR priority — mark critical ones higher and keep low-priority deferred.
Encoder reading: quadrature encoders need both-channel sampling or hardware quadrature decoder to avoid missed counts at high speed.
Sensor calibration: store calibration constants in EEPROM and apply on startup; saves repeated field calibration during maintenance.
Power sequencing: some peripherals require Vcc ordering; check datasheet and add soft-start if necessary to avoid latch-up.
UART baud error: small clock error accumulates; calculate max allowable baud error (%) to keep communication stable — exam fav topic.
Use software state machine for protocol handling — easier to test than spaghetti if-else statements; diagram states on paper first.
Always place 0.1uF decoupling near MCU Vcc pins — exam loves this basic hardware practice for stable operation.
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| Basic MCQs in Electrical Engineering | Visit post |
| Ohm's Law & Circuit Tricks | Visit post |
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| Digital Electronics Short Notes | Visit post |
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