Hello Torsten,
Your symptoms do seem to suggest either a short somewhere on the board, or a faulty MCU. I am not familiar with the 9S12NE64 - I assume that the pin PS6 is not an input only pin, when not using the SPI. With the SPI enabled, and with CPOL now set to 1, the static state of SPI_SCK should definitely be high.
Regards,
Mac