AT83C5123 Datasheet, ATMEL Corporation

* 80C51 Core :
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  – 6 Clocks per Instruction
  – Speed up to 16 MHz 768 Bytes RAM AT83C5122: 32 K.

AT8xC5122 retains the features of the Atmel 80C51 with 32 Kbytes ROM capacity, 768 bytes of internal RAM, a 4-level int.