Aduc7020 spi in slave mode, CS pin p1.7 grounded. Then, after reset, no data available on MISO. If CS not grounded during reset, but grouded manualy after reset - all is ok. Can I ground CS pin?
If you do not use the /CS signal you have no control about start and stop of a frame.
You may use a GPIO from the ADuC7021 itself to toggle the /CS, but still there is a potential problem if you have noise on the SPICLK. This can cause a extra bit shift on the SPI and without a more complex workaround using the PLA, the only solution is to do a SW-RESET of the whole part to resolve this. So the other direction - use ADuC7021 as Master is more solid.