The 20-TSSOP package gives you 18 I/O lines in a compact surface-mount footprint.
16 MHz core and memory — sizing the firmware budget
The 16 MHz clock is the maximum core speed; the internal oscillator means no external crystal is needed for basic operation. With only 4 KB of Flash, the firmware must be lean. The 1.5 KB of RAM limits data buffering.
For new designs, this means no imminent obsolescence risk.
