PDF datasheet for the Atmel AT89S51, an 8051-compatible microcontroller with 4 KB of in-system programmable flash and 128 bytes of RAM.

Full datasheet for the ATmega32 AVR microcontroller in PDF form, 2.70 MB. It describes the pinout, memory, clock options, timers, ADC, USART, SPI, TWI, JTAG interface…