Following pin connection between Teensy 3.2 and STM32 are exist when the ST4 cabel is connected (SHC with OnStep).

     Teensy            STM32
PIN 7 (TX2)  ->   PIN A6 (DEC-)
PIN 8 (RX2) ->    PIN A7 (DEC+)
PIN 6            ->   PIN B1 (RA-)
PIN 9            ->   PIN B0 (RA+)
VIN               ->   5V
GND             ->   GND

Anyone knows this is correct?