16 MHz ultra-low-power MCU in a through-hole DIP
Memory and speed — what fits in 2 KB
2 KB of Flash is the tight constraint here. A typical UART bootloader, a few sensor drivers, and a simple state machine will fit; anything involving a USB stack, a real-time OS, or a large lookup table will not. The 256-byte RAM limits data buffers — plan for single-packet or single-sample processing rather than buffering large blocks. The 16 MHz clock is generated from the internal oscillator, so no external crystal is needed for most applications. If timing accuracy better than a few percent is required, the internal oscillator's calibration holds within ±1% over temperature and voltage per the family datasheet — adequate for UART baud-rate generation.
No external LDO is needed when running from a coin cell or two AA batteries.