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MSP430FR2633: MSP430 BSL mode via serial port - shorting TX/RX

AI31
Expert 1600 points
Part Number: MSP430FR2633
Other Parts Discussed in Thread: SN65HVD75

Hello, 

- I'm using the SN65HVD75DRBT on the Serial Port of MSP430FR2633 to drive RS485 in half duplex mode.

- I also want to enable UART BSL in case FW upgrades were needed.

- I saw MSP430™ FRAM Devices Bootloader (BSL) SLAU550Z–January 2014–Revised March 2020 says that the device can be programmed in HALF DUPLEX mode.

Question:

Will I be able to use this circuit to program the device using RS485? (When the MCU is not driving DE and nRE, both the RS485 TX and RX will be enabled which is equivilant to shorting the UART pins of the MCU)

Will this shorting mess up the boot loading?

The main reason I'm doing this is the MCU won't be able to drive the DE/nRE signals while it is being programmed, correct?

  • 0
    TI__Mastermind 37015 points

    Hi Ahmed

    That looks fine. What's the host do you want to use? PC or MCU? 

  • 0 in reply to Gary Gao
    Expert 1600 points

    Hi Gary, 

    Thanks, I'm using a beagle board with another SN65HVD driver. So it's like flashing the MSP430 using the beagle as a linux host

    I was just worried about shorting the TX/RX from the MSP430 side

  • 0 in reply to AI31
    TI__Mastermind 37015 points

    What's the "shorting" meaning? Connect TX and RX directly? I don't see you shorting them in your schematic above.

  • 0 in reply to Gary Gao
    Expert 1600 points

    I mean through the SN65HVD75 chip... let me explain again, 

    1- The MSP UART pins are connected to the SN65HVD75 R and D pins.

    2- this SN65HVD75  is half duplex, please check its datasheet, when DE and ~RE pins are connected like that , the DE and RE are enabled, but again this is half duplex (so what you send on the D pin will be looped back to R, and hence back to the MSP)

    3- I want to program the chip via RS485_A and RS485_B pins. when the MSP is in BSL mode, I don't expect it to pull up and down DE and RE pins to control the communication.

    Check that schematic clearer

    thanks

  • 0 in reply to AI31
    TI__Mastermind 37015 points

    If  you use the custom boot loader you can deal with the echo signal by your self but it can't be used for ROM based BSL.

    Recommend you choose a RS485 transceiver without the echo function.

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