Datasheet for the Atmel AT89S52, one of the most popular 8051-compatible microcontrollers, with 8 KB of ISP flash, 256 bytes of RAM and three 16-bit timers. The 263 KB PDF lists pin functions, memory map, SFRs, power-down modes and the serial programming protocol. Repair technicians and hobbyists use it to check oscillator, reset and port pins when a board stays dead, or to wire an ISP programmer. Confirm the package version on the board, as DIP, PLCC and TQFP pin numbers differ.
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