STM32 BluePill SCServo (Waveshare/FeeTech) SDK port for LL

Library uses STM32 USART Single Wire (Half-Duplex) and controls motor directly without TTLinker / SCM-1 / FE-URT-1 / Buffer Circuits etc.

In USART Single Wire mode Pin is configured as open-drain and require external pull-up resitor (~500..1000 Ohm) to 3.3V.

  ┌──────┐          6..8V        ┌──┬─────┬──┐
  └─┬──┬─┘            ▲          │  │ USB │  │
┌───┴──┴───────────┐  │          │  └─────┘  │
│                  │  │   ┌───3V─┤ 3.3V      │
│                  │  │  ┌┴┐     │           │
│              PWR ├──┘  │ │ 1kΩ │           │
│  SC15            │     │ │     │  BluePill │
│                  │     └┬┘     │           │
│             DATA ├──────┴───30─┤ PA9       │
│                  │             │           │
│                  │             │           │
│              GND ├──────┬──GND─┤ GND       │
└──────────────────┘      │      └───────────┘
                          │
                         ─┴─

Library itself is well-designed, but some modifications were required for use with LL.

• Add as submodule or clone into your project folder.
• Configure in CubeMX (Cube configuration tool) USART as Half-Duplex (default servo baudrate is 1000000), enable USART Global Interrupt, code generation LL.
• In code:
  • Put USART_HD_IRQHandler() into USARTx interrupt routine
  • Call USART_HD_PostInit() after peripheral initialization
• Use

There is a variable in SCS.c called End, which determines endiannes conversion between servo and mcu. For STM32 it should be set to 1.

Source: FeeTech SCS SDK