Serial peripheral interface/ inter-IC sound (SPI/I2S) RM0390
854/1328 RM0390 Rev 4
– NSS output enable (SSM=0,SSOE = 1): this configuration is only used when the
MCU is set as master. The NSS pin is managed by the hardware. The NSS signal
is driven low as soon as the SPI is enabled in master mode (SPE=1), and is kept
low until the SPI is disabled (SPE =0).
– NSS output disable (SSM=0, SSOE = 0): if the microcontroller is acting as the
master on the bus, this configuration allows multimaster capability. If the NSS pin
is pulled low in this mode, the SPI enters master mode fault state and the device is
automatically reconfigured in slave mode. In slave mode, the NSS pin works as a
standard “chip select” input and the slave is selected while NSS line is at low level.
Figure 310. Hardware/software slave select management
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