BTT-Expansion-module
                                
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                        Pinout Diagram BTT Exp Mot+(Skr 1.4T,Skr1.4,Skr1.3) - Klipper Users
For configuration on the Klipper fimware it is necessary to know from the Skr 1.4T + Exp Mot which hardware pins (En, Step, Dir) (UART) (Spi Miso, Spi Mosi, Spi Sck) are located on the exp mot board, the same applies to other cards when connected to the exp mot.
https://github.com/bigtreetech/BTT-Expansion-module/blob/master/BTT%20EXP-MOT/BTT%20EXP-MOT%20V1.0-SCH.pdf
Uart_pin?