RPi and 7i90 via SPI, estop

Hello everybody!
I am new to this forum, so first I want to thank everybody for all the information posted here.
I want to replace my old 32-bit computer running a 3-axis stepper cnc via a parallel port. 
What I succeeded in:

1. I bought a Raspberry Pi 4 and a Mesa 7i90 card.
2. I used my old computer with parallel port, connected to the 7i90 and programmed the 7i90_spi_svst4_8.bit firmware using mesaflash.
3. I downloaded the LinuxCNC disk image for the RPi 4 and installed it.
4. I connected the 7i90 to the Raspberry Pi (about 3 inch flat-cable, all ground lines connected). I can read the device configuration using mesaflash without problems (well after a new install of mesaflash from the git repository).

Now I want to start ``linuxcnc linuxcnc/configs/by_interface/mesa/hm2-stepper/7i90-rpi-spi.ini``. The GUI pops up and everything seems fine.
But when I press F1 to reset the estop latch nothing happens. Up to now I did not connect any drivers or switches to the 7i90.
I changed 'DEBUG = 0x7fffffff' in the ini-file and added a 'show' to the end of the ini-file. I attach the output when running the linuxcnc. I marked what happend when I pressed F1 by '******' in the text.
If you need more information (ini-file, hal-file) let me know.
Many thanks for any support, H. Hermes