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Asserting on Chip Select
The SPI protocol requires that the SPI master asserts a SPI slave's chip select pin prior to starting a SPI transaction. While this protocol is generally followed, various types of SPI peripherals have different timing requirements as to when and for how long the chip select pin must remain asserted for a SPI transaction.
Commonly, the SPI master uses a hardware chip select to assert and de-assert the SPI slave for every data frame. In other cases, a SPI slave imposes the requirement of asserting the chip select over several SPI data frames. This is generally accomplished by using a regular, general-purpose output pin. Due to the complexity of such SPI peripheral implementations, this SPI driver has been designed to operate transparently to the SPI chip select. When the hardware chip select is used, the peripheral automatically selects/enables the peripheral. When using a software chip select, the application needs to handle the proper chip select and pin configuration. Chip select support will vary per SPI peripheral, refer to the device specific implementation documentation for details on chip select support.
Hardware chip select No additional action by the application is required.
Software chip select The application needs to handle the chip select assertion and de-assertion for the proper SPI peripheral.
