
Serial peripheral interface / integrated interchip sound (SPI/I2S)
RM0453
1264/1454
RM0453 Rev 2
Figure 350. Master and three independent slaves
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 I/O alternate function input/output section (GPIO)).
37.5.4 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.
Rx shift register
Tx shift register
Rx shift register
Tx shift register
SPI clock
generator
Master
Slave 1
MISO
MOSI
SCK
NSS
MISO
MOSI
SCK
NSS
(1)
Rx shift register
Tx shift register
Slave 2
Rx shift register
Tx shift register
Slave 3
IO1
IO2
IO3
MISO
MOSI
SCK
NSS
MISO
MOSI
SCK
NSS
MSv39626V1