Analyze the W1209WK board, and find out if board support is worthwhile.

[TG9541]

Reverse circuit-bend the module, and write some docs.

[TG9541]

Results are here: https://github.com/TG9541/stm8ef/wiki/Board-W1209WK

[TG9541]

Not done yet: some of my notes can as well be added to the Wiki.

[TG9541]

A serial interface through the ICP header (PD1/SWIM) works. The downside is that usage of the segment DP is restricted, and also the front panel key "C/F" can't be used while a PC is connected.
A test showed that using the "beeper" pin (PA1, capacitor) is more complicated (it requires NRZ encoding, e.g. Manchester Code, for reliable operation).

[TG9541]

The 7S-LED MPX together with serial communication works. To improve reliability the display now has 3 modes:

1. com mode with the display switched off to improve com reliability
2. display-com mode for interactive use
3. normal display operation (enter must be pressed repeatedly to enter mode 2.

Mode 1 is entered as soon as a character on the serial interface ipeseminenos received. After a first timeout Mode 2 is entered. After a second timeout mode 3 is entered.

EDIT: PD1 is not only used by the 7S-LED segment DP but also by the "C/F" front panel key. When PD1 is also used as a COM port, pressing this key can trigger a COM interrupt. I can't see an easy work-around. Maybe a different GPIO (a 7S-LED segment driver) will have to be used.

[TG9541]

The branch W1209WK contains a test implementation cb6871f. The key C/F sometimes triggers a serial COM interrupt, but all features work, and the board is usable.