Chip selects are optional. You can daily chain multiple spi devices and push the data out in a contiguous block. All the chip selects are tied together and only one cs line is used from the cpu.
For some simple SPI devices, sometimes. Many SPI devices, especially more complex ones, won't let you shift data through the device without attempting to interpret it.
Or will shift out something completely different, like the response to the last command they received, just FFs so you can three wire in the general case, or even just garbage.
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Chip selects are optional. You can daily chain multiple spi devices and push the data out in a contiguous block. All the chip selects are tied together and only one cs line is used from the cpu.
For some simple SPI devices, sometimes. Many SPI devices, especially more complex ones, won't let you shift data through the device without attempting to interpret it.
Or will shift out something completely different, like the response to the last command they received, just FFs so you can three wire in the general case, or even just garbage.
Flash memory devices use the CS line as an integral part of the protocol. It is definitely not optional.