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LAUNCHXL-F28377S: no UART connection after power-up

LAUNCHXL-F28377S user
Prodigy 165 points
Other Parts Discussed in Thread: CONTROLSUITE

Hi,

I have a problem with the LaunchXL-F28377S. When I put the USB-Kabel in and try to communicate by UART, this is not possible. When I press reset after that, UART communication is working fine. The code at the Controller is running but the communication is not working at power-up. I am booting from Flash an tried it with both TRST positions. All wait-state options are at default (maximum). I am using the GPIO 84,85 over XDS100v2. Everything works fine but not after power-up.

I tried it on two devices.

Is there an issue to solve the problem by software?

Greetings

  • 0
    Guru 30330 points
    Hi,

    Can you confirm that None of your code works after a power up in standalone mode? Is it only the SCI functions that are not working?

    It looks like the Boot Mode Select switches on the Launchpad are GPIO84 and GPIO72. So there may be contention while using GPIO84 as a boot mode, but then also pulled up to enable the Get Mode which defaults to boot to FLASH.

    Thanks,
    Mark
  • 0 in reply to Mark Labbato
    Prodigy 165 points

    Hi,

    yes it is only the SCI function which is not working.

    I also thought about the GPIO84 but there is no difference on this pin at power up or reset. It is pulled up with 700 ohms to 3.3V all the time and after reset it works.

    But now i tried some more things and when i give power to the XDS100V2 first and after that to the µC, it works too. (By setting JP1 after put on the USB cable)

    So there is a communication problem between FT2232H and µC when µC powers up to fast? Can I make the power up of the µC slower or is it possble to do a software reset once after power up?

  • 0 in reply to LAUNCHXL-F28377S user
    Prodigy 165 points

    Hi,

    I found a solution. A 220µF capacitor between reset and ground solved the problem. Looks like there is an internal 3.6 kOhm pull-down resistor, so I can't replace the 2.2kOhm resistor between reset and VDD on the pcb.

    Are there any other solutions by code? For example switching of the pull-down resistor to use a smaller capacitor. I can't find anything about it in the manuals.

  • 0 in reply to LAUNCHXL-F28377S user
    TI__Guru 57255 points

    Hi,

    It is good that you found a solution.  However, it might not be a good one in many circumstances.  For instance, the big RC time constant you have on XRSn will hinder the ability for the device to successfully do a watchdog reset.

    I am not aware of the internal 3.6kOhm pull-down resistor that you speak of.

    Some thoughts on the problem you are seeing:
    1) I might recommend taking a look at VDDIO, VDD, and XRSn as the device is powering up.  Based on what you are saying (before you added the big capacitor), I suspect that VDDIO and/or VDD are unstable for awhile after the USB is plugged in.  Furthermore, XRSn may be getting released before VDDIO and VDD are stable.  Or perhaps VDD is becoming greater than VDDIO during power up.
    2) I suspect that the root cause of what you are seeing may be due to your computer's USB drive strength and the length of the USB cables you are using. 
    3) We recommend utilizing an external voltage supervisor (SVS) to help remove these type of issues.  You can refer to the F28379 controlCARD schematic in controlSUITE for a potential SVS solution.


    Thank you,
    Brett

  • 0 in reply to Brett Larimore
    TI__Guru** 109155 points

    I agree with Brett's concern on high value of capacitance.  In Datasheet it's mentioned that the value of capacitance should be less than 100nF.

    Regards,

    Vivek Singh

  • 0 in reply to Brett Larimore
    Prodigy 165 points
    Hi,

    thanks for this very helpful awnser.

    About yout thoughts:
    1) I think you are right.
    2) I tried it at least with the blank LAUNCHXL with the original cable on two different computers, both with usb2 and usb3.
    3) Thanks for this advice. I will try this solution.