Single-cycle microcontroller with 8KB ISP flash, 12-clock compatibility mode, 256 bytes flash data memory, 256 bytes RAM, three timers, UART, WDT, up to 36 I/Os, and an internal RC oscillator.

100% software and timing compatibility with AT89S52, meaning no changes to existing software, including fetching from external ROM or read/write from/to external RAM.Disable compatibility mode to achieve on average 9 times more throughput at the same current consumption and frequency as AT89S52, or lower the clock frequency 9 times and achieve the same speed as AT89S52 but with more than 5 times less current consumption.Save even more power and the cost of the quartz crystal altogether by using the internal 1.8432 MHz RC oscillator, which is Vcc and temperature compensated well enough to ensure proper UART serial communications.