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 suffix. This 278 KB PDF should give pinouts for DIP, PLCC and TQFP packages, SFR definitions and parallel programming details. Use it when servicing industrial controllers or legacy equipment built around larger 8051 parts. Confirm the exact suffix on the chip, as the watchdog version and the earlier AT89C55 differ in features and programming.
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