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MSP432E411Y-BGAEVM: Do I need the SSI Fss pin?

Genius 5915 points
Part Number: MSP432E411Y-BGAEVM

Hi,

My customers are using two MSP432E411Y-BGAEVMs to check the SSI (Freescale format).

When Fss was set, they was able to confirm the operation of SCLK=1MHz,
However, when Fss is not set, Slave data cannot be read. (They was successful at 200kHz.)

Question 1:
Is it possible to use SSI communication without FSS pin?
Do you know why communication is successful when SCLK is set low?

Question 2:
How long should I wait after setting FSS to Low before sending data?

Regards,

Rei

  • Hello,

    Question 1:
    Is it possible to use SSI communication without FSS pin?
    Do you know why communication is successful when SCLK is set low?

    I found this in the technical reference manual (TRM):

    The Freescale SPI interface is a four-wire interface where the SSInFss signal behaves as a slave select. If operating in legacy mode and using the Freescale SPI frame format, the inactive state and phase of the SSInClk signal are programmable through the SPO and SPH bits in the SSICR0 control register. If operating in advanced-, bi-, or quad-SSI mode, the SP0 and SPH bits must be programmed to 0.

    The FSS signal is equivalent to the SPI CS in Freescale mode according to these threads.

    Question 2:
    How long should I wait after setting FSS to Low before sending data?

    This should be handled by the SSI module. I would recommend reading through the TRM to learn more.