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What is NSS pin in SPI?
The active-low slave-select (NSS) signal allows support for multiple slave devices on a single bus. It is also used to detect the start and end of a SPI transfer for CP2400/2, and should be connected to the SPI master instead of connection to a static low level signal, e.g. GND.
What is hardware NSS signal?
Hardware NSS management (SSM bit = 0). This has two possible configurations depending on the SSOE bit in register SPIx_CR1: NSS output enable (SSOE = 1). Only used when the MCU is master. The NSS signal is driven low as soon as SPI is enabled in master mode (SPE=1) and is kept low until SPI is disabled (SPE=0).
What is NSS pulse mode?
The Slave Select signal can operate in a pulse mode where the master generates pulses on NSS output signal between data frames for a duration of one SPI clock period when there is a continuous transfer of data. The data is then interleaved by two SPI clock periods. The clock phase is fixed in this mode.
How SPI works in STM32?
SPI is a bus, which means you can use multiple peripheral devices for one controller. All of the lines are shared except for the CS line. You will need to dedicate one pin on your controller as a separate CS line for each peripheral you wish to communicate with.
Can SPI be half duplex?
The SPI can communicate in half-duplex mode by setting the BIDIMODE bit in the SPIx_CR1 register. In half-duplex data communication, one single cross-connection line is used to link the shift registers. Or the master sends the data on the MOSI line, and the slave gets it. The MISO line of the master remains inactive.
How to use the NSS pin as a GPIO?
You can use the NSS pin as a standard GPIO and drive it with an interrupt routine.You should do that part by software.First put the Nss low and then send your frame (HAL_SPI_Transmit) After the slave gets all frame, use the HAL_SPI_RxCpltCallback and put the Nss high in that interrupt. Dont forget to connect GPIO pin to Nss pin on slave.
How is the NSS pin of the Master connected?
The NSS pin of the master is connected to +VDD to avoid some errors otherwise leave that pin as unconfigured. If the NSS pin, configured by using GPIO alternate functionality, then connect NSS pin to +VDD.
When to enable or disable SPI on NSS?
The NSS signal is driven low as soon as SPI is enabled in master mode (SPE=1) and is kept low until SPI is disabled (SPE=0). A pulse can be generated between continuous communications if NSS pulse mode is activated. The SPI can not work in multimaster configuration with this NSS setting NSS output disable (SSOE = 0).
What happens to the NSS pin when SSI is 0?
So, if SSM=1 and SSI=0 then the NSS pin will ground internally. That means the slave is selected, and then the salve can communicate with the master. So, here you need not use the NSS pin. If SSI=1, then NSS pin will pull to high or VDD and if SSI=0, then NSS pin will pulled ground or 0.