Compact ATmega328P board with breadboard-friendly headers.
Reset, clock, debug, USB, crystal and analogue-reference pins have special electrical or boot functions. Avoid loading them until the boot sequence is understood.
Check BOOT/RESET/programming pin truth tables before assigning peripherals; keep required pull resistors fitted.
5 V domain. Never exceed VDD + permitted injection limits; level-shift incompatible modules and share ground only where safe.
Start with the memory map: code flash, SRAM, peripheral registers and system/control space. Use vendor headers instead of hard-coded addresses, then study GPIO direction/output/input, clock-enable, interrupt and timer registers.
Choose this device only after checking logic voltage, required interfaces, memory margin, timers/ADC resolution, debugging access, package availability and long-term tool support.
Not detected: verify data USB cable, driver, boot mode and target power. Upload failure: select the exact target and programmer. Unstable operation: inspect supply ripple, reset, clock and watchdog cause. Wrong readings: check reference voltage, grounding, pin multiplexing and calibration.
Absolute maximum prevents damage; reliable design stays within recommended operating conditions.
Many MCUs gate clocks to save power; registers may not operate until the peripheral clock is enabled.
It enables programming, breakpoints, fault inspection and production recovery.
Over-voltage, excess source/sink current, negative injection, ESD or driving against another output.
