Hi Luuk Grefte,
Your pin function configuration is not correct, please check the user manual. I have checked it, SPI function in PIO2_0, PIO2_1, PIO2_2, PIO2_3 is all function 2.
Take an example:

Chip_IOCON_PinLocSel can be found in iocon11xx.h, in the lpc_chip_11cxx.lib.

Please modify the pin function to 2, then try again.
If you still have question, please let me know!
Have a great day,
Kerry
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