Datasheet for the Atmel AT89C55, an 8051-family microcontroller with 20 KB of reprogrammable flash and 256 bytes of RAM, supplied as a 421 KB PDF.

Atmel datasheet for the AT89C55WD, an 8051-compatible microcontroller with 20 KB of flash, 256 bytes of RAM, three timers and a watchdog timer, as reflected by the WD…