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RM48L952: SPI and Ethernet Incompatability

John McLaughlin22
Prodigy 180 points
Part Number: RM48L952
Other Parts Discussed in Thread: HALCOGEN

Hello,

I am using the Hercules RM48L952 development board. I am trying to obtain data using a SPI interface (as a master) and send data using the Ethernet interface.

I have tested SPI1 and SPI2 (I have not tried SPI3 or SPI5 yet), but I can only send SPI transmissions using these peripherals when the Ethernet switch on the board (on a set of switches labeled S2) is turned off. This implies there are lines for SPI and Ethernet that are muxed on this board, but I have poured through the datasheets and looked at the Halcogen PINMUX tab, and I can't see anything regarding this.

Is it possible to use SPI and Ethernet on this board for the same application?

John

  • 0
    TI__Guru 68920 points

    John,

    On the HDK there are bus switch devices that are controlled by S2.  You need to look at the schematics or check the board user's guide to understand these switches.  They are not part of the MCU's internal pinmux they are board level.

  • 0 in reply to Anthony F. Seely
    Prodigy 180 points
    Is there anyone familiar with the HDK board who can explain why enabling the Ethernet switch on S2 seems to disable SPI communication? Reading schematics is not my strong suit, and the user's guide provides no insight on this issue.

    John
  • 0 in reply to John McLaughlin22
    TI__Guru 68920 points
    S2 controls how several sets of signals are routed on the PCB.

    So in one position you might have your SPI signals connected to the expansion header. If you flip the switch, they are disconnected from the expansion header and presumably connected to Ethernet.

    You still need to change the pinmux to make the function of the pin appropriate for where the connection is going to on the board.

    The switch on the board helps limit how many loads are connected to a signal when it is used for something critical like ethernet where the signalling may be 50MHz. But that is like a 'wiring' connection.

    The pinmux in HalCoGen controls the protocol of the pin by determining which peripheral drives the pin.

    hope that makes sense.
  • 0 in reply to Anthony F. Seely
    Prodigy 180 points
    So I actually discovered the problem when pouring through the schematics for the board.

    As it turns out, the Ethernet switch on S2 serves as an enable signal for several muxes on the board. The lines for SPI1, SPI3, and SPI5 each go through these muxes one way or another. The HDK board essentially disables these peripherals if one tries to enable Ethernet.

    SPI2 is the only SPI peripheral that's not affected by this, but I have another issue with it that I will describe in another post.