SPI and PC_3C as output

Official Hardware Portenta Family Portenta H7
1

If I run the following code on the Portenta H7 I can measure the MOSI Signal on the Port PC_3C.
Does somebody know why?

#include <SPI.h>

uint8_t data = 0;

void setup()
{
pinMode(PC_3C, INPUT);
SPI.begin();
SPI.beginTransaction(SPISettings(48000000, MSBFIRST, SPI_MODE0));
}

void loop()
{
SPI.transfer(data++);
}

2

If I do that, nothing is send over the SPI Port.
Some ideas?

#include <SPI.h>

uint8_t data = 0;

void setup()
{
//pinMode(PC_3C, INPUT_PULLUP);
SPI.begin();
SPI.beginTransaction(SPISettings(48000000, MSBFIRST, SPI_MODE0));
}

void loop()
{
analogRead(PC_3C);
SPI.transfer(data++);
}