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TPS65986: can't pass through UART

JAP
Intellectual 2410 points

Part Number: TPS65986

Dear Experts,

I'm working with a USB Type-C design where TPS65986 is used as a PD-controller. Intention is to use debug accessory mode to pass UART through TPS65986. TPS65986 recognizes debug-cable and enters in debug accessory mode but is not passing UART. C_USB_TP is connected to C_USB_BP and C_USB_TN is connected to C_USB_BN on connector side. UART has been tried to route to USB_RP_P/N and UART_RX/TX but without success. It seems that for some reason crossbar MUX is not changing its state. What could cause behavior like this?

Rgds,

Juha

  • 0
    TI__Mastermind 36756 points
    Hi Juha,

    The UART lines on the TPS65986 can only be used to UART boot a second TPS65986. If you had two TPS65986's on your board, you could share one SPI flash between the two and have the primary 86 UART boot the secondary 86. The crossbar mux cannot be configured to pass the UART lines over the USB2.0 lines.

    Thank you,
    Eric
  • 0 in reply to Eric Beljaars
    TI__Intellectual 2410 points
    Hi Eric,

    I'm a bit confused. According to datasheet "The CORE_UARTn connections come from a digital crossbar multiplexer that allows the UART_RX/TX to be mapped to any of the 1st stage multiplexers.".

    Doesn't this mean that UART signals should be possible to route to at least some of the USB2.0 lines? Can you clearly explain what pins can be used for UART in debug accessory mode?

    Thanks!


    Rgds,
    Juha
  • 0 in reply to JAP
    TI__Mastermind 36756 points
    Hi Juha,

    Our firmware does not support routing the UART lines over the D+/D- lines as this would be non-compliant behavior per the USB Spec. The UART lines are only used for booting a secondary device during bootup on the TPS65986.

    Thank you,
    Eric
  • 0 in reply to Eric Beljaars
    TI__Intellectual 2410 points
    Hi Eric,

    Ok, thanks. Would it be possible to use USB_RP_P/N instead? C_USB_TP/N or C_USB_BP/N can be connected to USB_RP_P/N via 2nd stage, right? How about passing UART through those pins?

    Rgds,
    Juha
  • 0 in reply to JAP
    TI__Mastermind 36756 points
    Hi Juha,

    You would need to use some sort of UART to USB protocol converter as UART is not a compliant form of communication on the Type-C connector. The C_USBTP/N and C_USB_BP/N are the USB D+/D- lines from the connector. These are then muxed to the system side USB_RP_P/N depending on the orientation of the cable.

    Thank you,
    Eric