The SPI has the capability to operate in multimaster environment. Consequently, the NPCS0/NSS line must be monitored. If one of the masters on the SPI bus is currently transmitting, the NPCS0/NSS line is low and the SPI must not transmit any data. A mode fault is detected when the SPI is programmed in Master mode and a low level is driven by an external master on the NPCS0/NSS signal. In multimaster environment, NPCS0, MOSI, MISO and SPCK pins must be configured in open drain (through the PIO controller). When a mode fault is detected, SPI_SR.MODF bit is set until SPI_SR is read and the SPI is automatically disabled until it is reenabled by setting SPI_CR.SPIEN bit.
By default, the mode fault detection is enabled. The user can disable it by setting SPI_MR.MODFDIS bit.