The CH55x is an 8-bit enhanced E8051 core MCU compatible with the MCS51 instruction set. 79% of its instructions are single-byte single-cycle instructions, and the average instruction speed is 8 - 15 times faster than that of the standard MCS51. The special xRAM supports direct memory access (DMA), data fast copy command, and double DPTR pointers. The CH55x has a built-in USB controller and USB transceiver, it supports USB-Host mode (except CH552) and USB-Device mode, USB Type-C master-slave detection (except CH559), USB 2.0 full-speed (12Mbps) and low-speed (1.5Mbps) traffic, data packets of up to 64 bytes, and DMA. It has a factory built-in bootloader so firmware can be uploaded directly via USB without the need for an additional programming device.
Note: The CH559T partially has a different pinout. Refer to the datasheet for more information.