Starting to work on the HC12

The HC12 is a Si4463 based RS232-RF modem in 433 ISM band. Compared with the average garage door remote RF solution the Si4463 is much more advanced (range, modulation modes, immunity to noise). It has so many features that the normal way to program it is to use a code generator provided by Silicon Labs, the manufacturer of the chip.

The other chip on the board is an STM8S003F3P6, and that's why I write about it. Some time ago @ajlitt forked the STM8EF repository to work on the HC12. He did the reverse engineering, and wrote first code to make the STM8S talk to the Si4463 (a mix of board-support code, and Forth). However, he had planned to implement a packet radio protocol that needs more RAM than the STM8S has to offer.

I have a much more humble use case: bring Forth into the STM8S of the HC12, and have it communicate with an off-the-shelf HC12 through the Si4463 radio.

Some time ago I ordered 3 x HC12 modules that now have the following roles:

• one with unmodified firmware connected a logic analyzer
• one serving as development target
• one with unmodified firmware as a reference

The HC12 connected to the logic analyzer is necessary to understand, and re-implement the Si4463 API calls and parameters.

I now implement the initialization, and the communication routines. There is an "issue", and some docs on GitHub.