keyboards/handwired/splittest/bluepill/readme.md
This is the splittest example for the bluepill MCU. To trigger keypress, short together pins B10 and B1.
The type of communication (bitbang, serial (half/full duplex)) is set by the keymap config.h file with variables with SPLIT_ prefix.
So this example uses:
config.h to set which SDI to use for serial. Either define USE_SDI1_ON_STANDARD_ROLE_PINS, USE_SDI1_ON_ALTERNATE_ROLE_PINS or USE_SDI2 before the #ifdef that configures the default case when none of these variable is defined.post_config.h for defining the communication pins between the halves once the keymap is configured.On your keyboard, you most likely will only use config.h because you'd have already chosen your communication scheme: serial type, SDI, pins.
Have a look at the handedness documentation
Choose one of the connection type
Check the documentation to determine the pull-up resistor.