I've got a design with MK20D512 microcontroller, which is supposed to communicate over SPI as slave. According to the user manual, the SPI slave gets activated when the "slave select" ie. PSC/nSS signal is asserted. However, in this case the "slave select" line is not available, and not connected to anything.
Is it possible to manually activate the SPI slave for transfer? For example, can the true "slave select" signal be set or cleared by activating internal pull-up or pull-down resistor (PORTx_PCRn, bits 1 and 0)?