E-paper display drive IC usually has a busy pin to tell MCU the current working state of E-paper. When E-paper display is refreshing normally, the busy pin will be in the busy state. At this time, MCU cannot read and write the IC.
Feedback from some clients reported that at the beginning of debugging, e-paper initialization is easy to get stuck in busy judgment function. Here are some possibilities for the situation:

1. SPI serial communication fails, and the IC does not work normally. At this time, the busy pin is always in the low-level state.
2. The E-paper display supply voltage is low, resulting in the IC not working normally.
3. The E-paper display FPC is inserted reversely, usually with the golden finger upward, resulting in the IC not working normally.
4. E-paper driver error. Generally, e-paper ICs are divided into SSD series and UC series. The busy status of these two ICs is reverse.
5. The busy pin is not normally connected to the circuit, resulting in the MCU always judging that busy is in the busy state.

The following is the sequence diagram of busy pin when E-paper display refreshes