Datasheet for the Atmel AT89C1051U, a 20-pin 8051-compatible microcontroller with 1 KB of flash; the U version adds a UART and second timer compared with the basic AT89C1051. The 268 KB PDF lists the pinout, comparator function, memory organisation, electrical characteristics and programming procedure. It is useful when repairing compact control boards in small appliances or when choosing a replacement. Check that the U suffix appears on the fitted chip, since firmware using the serial port will not run on the plain part.
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