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SPI(4 pin mode (STE)) of MSP430F5438 AS chipselect

ANOOP G S
Intellectual 305 points
Other Parts Discussed in Thread: MSP430F5438

sir,

I need an information on SPI(4 pin mode (STE)) of MSP430F5438.Can we use STE as Automatic chipselect to a slave device.Or need to switch a port pin for this purpose.Although i made the processor for 4 pin mode (UCMODEx to 4-pin SPI with UCxSTE active low: Slave enabled when UCxSTE = 0) .I can't get the real effect.Using a GPIO as chipselect  may take some more delay.I have to make some quick processes with spi in MicroSeconds.Please give your valuable help. 

Regards,

ANOOP G.S.

PROJECT ENGINEER 1

CENTRE FOR DEVELOPMENT OF ADVANCED COMPUTING

TRIVANDRUM


  • 0
    Guru 35565 points

    ANOOP G S said:
    I can't get the real effect

    What, exactly, do you mean by that?

    http://www.catb.org/~esr/faqs/smart-questions.html#beprecise

     

  • 0
    Guru 227245 points

    ANOOP G S said:
    Can we use STE as Automatic chipselect to a slave device.Or need to switch a port pin for this purpose

    Both :)
    The STE signal in slave mode just shuts down teh output driver on SOMI pin and disables the clock reception. It does not trigger an interrupt or reset the state machine (which is usually required, as teh CS signal is also a syncsignal for a byte border).

    So whiel STE ensures that the slave is immediately 'neutralized' and the bus is free for other transfers, you still need to detect this situation and handle it slave-internally. It is a good idea to connect the STE pin with an interrupt-capable port pin, so you get an interrupt on the CS change for both, low going CS for a transfer start (so you can prepare the slave output) as well as high-going interrupt (when the transfer ends, normally or prematurely)

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