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MSP430FR5969: Processor-to-Processor SPI connection

Ray Austin
Prodigy 110 points

Part Number: MSP430FR5969
Other Parts Discussed in Thread: MSP-EXP430FR5969

I'm laying out a board for our development group and need to connect two MSP430FR5969's via SPI. One as Master, and one as Slave. There are no other masters or slaves on the bus. From what I've read, I think it is as simple as connecting MOSI-MOSI, MISO-MISO, CLK-CLK, AND STE-STE. But I have also read other "opinions" that say differently. There seems to be a fair amount of confusion about the STE line. Has anyone actually done this, or know for sure?

Thanks,

Ray

  • 0
    Guru 102165 points
    It would be useful to know what "confusion" you've encountered.

    The slave has to use STE, since that's what will activate the SPI unit. (I suppose you could keep STE active all the time, but that makes for a poor bus citizen.)

    The master needs to provide a Chip Select to the slave's STE, but it doesn't need to be the (master's) STE pin, and it doesn't need to use the automatic assertion (UCSTEM). (I've never used UCSTEM, since it only provides for single-byte transactions.)
  • 0 in reply to Bruce McKenney
    Prodigy 110 points
    Hi Bruce,
    Thanks for the reply. I think the bit about UCSTEM only supporting single byte transfers will turn out to be important to us, since slave will be sending data in multi-byte words.

    As far as the confusion... I saw comments about the STE line only being an input, never an output. I think turned out to be wrong. Also comments about using STE as an output with multiple slaves, which didn't sound right. A few places where the answerer seemed to misunderstand the question, which also confused things.

    For my project then, it seems like the correct setup would be MISO-MISO, MOSI-MOSI, CLK-CLK, and Master GPIO to Slave STE.
    Does that sound like the default setup for one MSP Master talking to one MSP Slave, with multi-byte words?
  • 0 in reply to Ray Austin
    Guru 102165 points
    Yes, that's the idea. I'm pretty sure the "register level" examples (link from Product page) include an SPI master/slave pair, which might be instructive.

    [Unsolicited:] In my world a board spin costs thousands of dollars; a pair of Launchpads costs $32. Before you believe me (or anyone you meet on the Web), consider wiring up a couple of MSP-EXP430FR5969 to make sure there aren't any surprises. And you were going to write the software sooner or later anyway.
  • 0 in reply to Bruce McKenney
    Prodigy 110 points
    Good advice. Thanks for the help, Bruce.
    Ray

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