* * HARDWARE OVERVIEW * *

The CH552 is a little MCU with a 8051 core and a USB interface, and is damn cheap.

So far I have never used an 8051 core, so this seemed like a good opportunity to try it out.

So I bought a small lot of the SO-16 version (CH552G) and made a little board to play with it, the "CH552 Dragon"... :-)

The board follows the same "layout concept" of the previous ARMando, so can be directly inserted in one or two breadboards:

On the CH552 Dragon I've added a physical "user" key (USR) and three touch buttons (TIN1, TIN2 and TIN3) because the CH552 has the hardware to use them.

There is also an optional 3.3V power supply (you can choose not to populate it if not interested, see the schematic) to choose the GPIO supply between 5V or 3.3V (i.e. if you want connect 3.3V stuff) using the PWR SEL switch.

All the official documentation of the manufacturer (WCH) is written only in Chinese, but using Google Translator can be more readable for sure. Here a link to the CH552 page with automatic English translation.

* * SOFTWARE OVERVIEW * *

To program the CH55X MCU family it is available an open source C toolchain based on the SDCC compiler and can be found on Github.

In the same repository there is a english translation on the CH554 manual (the MCU version that adds the USB Host capability) and can be used for the CH552 too.

In the following video there is the usual blink test example:

To flash the executable .HEX file I've used here (on Windows 10) the original tool made by WCH (WCHISPTOOL) that can be found here.

The CH55X MCU comes with a bootloader that allows to use both the USB (used in the previous video) or the serial interface (the bootloader "eats" some of the flash space, and cannot be overwritten using the USB or serial interface).

To program the CH552 you need to power it with a 5V supply (the CH552 can work at 3.3V too but you can't program it. The PWR SEL switch, if populated, must be in the 5V position to allow the MCU programming), press the PROG button and then power it (i.e. attaching to an USB port).

It Is not possible to activate the bootloader pressing the RST and the PROG key, but a power-on is needed (with the PROG key pressed).

Remember also that accordingly with the datasheet the flash has a limited "guaranteed" number of 200 write cycles.

All the details and updates are in this page: https://hackaday.io/project/169671