At89sx 8 bit microcontroller atmel at89s51 24pu the atmel at89s range are low voltage high performance cmos 8 bit microcontrollers that feature in system programmable isp flash program memory manufactured using atmels high density nonvolatile memory technololgy these devices are compatible with the industry standard mcs 51 instruction set as well as being functionally compatible with the at89c2051 microcontroller by combining a versatile 8 bit cpu with flash memory on a monolithic chip