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TMS320F28065 SPIA as slave without SPISTEA (chip select)

Sergio Hernandez
Prodigy 30 points

Other Parts Discussed in Thread: TMS320F28065

Hi everyone.

I'm using the TMS320F28065 80pin package.  I need to lnow if it is possible to use the SPI-A as slave without the SPISTEA pin which is actually the Chip Select, since this pin is used as XCLKIN for the external clock input source.  It is not possible to move the external oscilator ti X1 - X2 because they can handle different clock frequencies.

Thanks in advance

  • 0
    Guru 30330 points

    Sergio,

    This is technically possible, but we do not recommend it.

    From the F2806x TRM SPRUH18F, Table 1-63. The default state of the SPISTEx input if no GPIO is assigned is 0, meaning, the SPI will always be enabled.

    This is not recommended because any incoming signal on the Clock line will cause data to be shifted in or out of the SPI Slave.
    Here is a good thread on what may occur if no SPISTE signal is connected and driven appropriately: e2e.ti.com/.../1576628 . A workaround is to ensure with software that the Master and Slave have some sort of periodic synchronization to ensure that the data is received correctly.

    Here is another similar thread on the topic: e2e.ti.com/.../1232725

    Is there any reason why you cannot move to SPIB for your Slave functionality?

    Regards,
    Mark

  • 0
    Prodigy 30 points
    Hi Mark.

    Thanks for the links I'll check the info.

    SPIB is already in use extracting data from a TI's ADC.

    SPIA will be read by the control and communications MCU to extract the proccessed data from the 28065.

    SPIA must be slave since:

    - Control & Comms MCU talks to other slave components
    - In the Control & Comms MCU's datasheet it's said that it doesn't work correctly as slave! (not TI MCU, no chance for a change)

    Regards.
  • 0 in reply to Sergio Hernandez
    Guru 30330 points
    Sergio,

    My suggestion would be to make the SPIB the slave to your Control and Comms port, since you have access to the SPISTEB signal. If you use SPIA as the master to extract data from the TI ADC, you can use a GPIO as a software controlled Chip select in place of SPISTEA.

    This would be a simple software change to swap SPIA and SPIB functionality. But I understand if your board is already built and not easily changed.

    -Mark
  • 0 in reply to Mark Labbato
    Prodigy 30 points
    Hi Mark.

    We're conssidering a further revision for the board. If it happens, it would include the SPI swap.

    By the main time I'll be looking forward to use the hardware as is, the link to te post you sent me is a good reference. I'm alraedy wonking in the firmware.

    Also, I would like to have your opinion on moving the oscilator signal from the GPIO19 (pin #52) to the GPIO38(pin #54) and have a couple jumpers to select either the on-board oscilator or the jtag incomming clock when debugging/programming. At this moment, GPIO38 is used only in the jtag header. TI's advice on this option would be highly appreciated.

    Thanks once again.

    Sergio
  • 0 in reply to Sergio Hernandez
    Guru 30330 points
    Sergio,

    I agree with the SPI swap, it is the most straightforward and should accomplish the things you would like without any special workarounds or software.

    I am no expert in clocking, but just looking at the pin descriptions, it looks like a perfectly acceptable use. We brought XCLKIN to multiple pins to allow the user to design their clocking scheme to suit their requirements. be sure that you have the proper hooks to allow for JTAG operation as well as standalone operation if you decide to go this route.

    I will forward this to our clocking expert to see if he has any additional input.

    Thanks,
    Mark
  • 0 in reply to Sergio Hernandez
    TI__Guru 55700 points

    In F28065, external clock can be provided by XTAL (or) external oscillator through GPIO19 (or) GPIO38.

     If you are planning to use crystal, you have to use X1/X2. Please refer Figure 6-12. Using the On-chip Crystal Oscillator in device datasheet.

     If you are planning to use external oscillator, you can use GPIO19 (or) GPIO38. Please refer Figure 6-13. Using a 3.3-V External Oscillator in device datasheet.