embedded - How can I broadcast data to multiple SPI slaves and how it works?

Question

I know basic SPI protocol and its master to slave operations. I want to know that is it possible to broadcast data on multiple slave? If it is possible then how it works.

I've heard that after writing to any SPI slave you have to read from slave even if you are not going to use read data. How is this possible in case broadcast if broadcast is possible?

Answer 1

No, it's not possible. Since SPI is 4- wire interface. The SS line is used for slave selection.One SPI master can have multiple slaves but it cannot select all the slaves at once since it is either using some bit or SS signal to select the slave(and cannot select multiple slave at a single time).

SPI works in full duplex mode(most of time and cases), and is implemented using shift registers. Hence while writing the data on MOSI(assumption: master is writing),we are getting the data in MISO line too (inserting data in master shift register does shift the data in slave shift register). Hence we get data on both of the TX and RX lines.