Figure 574. Master And Three Independent Slaves - ST STM32G4 Series Reference Manual

Advanced arm-based 32-bit mcus

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Rx shift register

Tx shift register

1. NSS pin is not used on master side at this configuration. It has to be managed internally (SSM=1, SSI=1) to

prevent any MODF error.

2. As MISO pins of the slaves are connected together, all slaves must have the GPIO configuration of their

MISO pin set as alternate function open-drain (see

Multi-master communication

Unless SPI bus is not designed for a multi-master capability primarily, the user can use build

in feature which detects a potential conflict between two nodes trying to master the bus at

the same time. For this detection, NSS pin is used configured at hardware input mode.

The connection of more than two SPI nodes working at this mode is impossible as only one

node can apply its output on a common data line at time.

When nodes are non active, both stay at slave mode by default. Once one node wants to

overtake control on the bus, it switches itself into master mode and applies active level on

the slave select input of the other node via dedicated GPIO pin. After the session is

completed, the active slave select signal is released and the node mastering the bus

temporary returns back to passive slave mode waiting for next session start.