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Bootstrap Loader (BSL) sharing UART port for field firmware updates?

Scott Brenneman
Genius 3265 points
Other Parts Discussed in Thread: MSP430F5336, MSP-FET

We want to enable our product (which uses the MSP430F5336) to be able to have its firmware updated via a serial port connector exposed to the outside world. That serial port uses one of the two UARTs, and also needs to present CTS and RTS on that connector for hardware handshaking. 

However, the standard BSL method ties DTR to RESET and RTS to TCK, which means that RTS is tied to two pins on the micro: PJ.3/TCK, and a standard GPIO.  This causes me to wonder a couple of things.

1.  In order to use a debugger like the MSP-FET430UIF, we'd need to disconnect RTS from the TCK net in order to prevent contention, correct?  I suppose we could put a jumper on the board which would be removed when the MSP-FET is in use.  Does this sound right?  Any other suggestions?

2.  During normal operation, will PJ.3/TCK mind being driven by RTS as it performs normal handshaking functions?  Can't we just put the PJ.3/TCK pin in GPIO mode, i.e. PJ.3 and set it as an input? 

Any other comments or suggestions on this?

Thanks,

Scott

  • 0
    Guru 227245 points

    Scott Brenneman said:
    In order to use a debugger like the MSP-FET430UIF, we'd need to disconnect RTS from the TCK net in order to prevent contention, correct? 

    Yes. However, this can be easily done by using a pullup resistor and a diode (e.g. BAT42). No jumper or switch or complex electronics needed.

    Scott Brenneman said:
    Can't we just put the PJ.3/TCK pin in GPIO mode, i.e. PJ.3 and set it as an input? 

    Unless my datasheet of the 533x is wrong, the entry sequence signals are on RST and TEST. So the default high level of inactive DTR signal will put PJ into JTAG mode.

    I'm prett ysure there is a combination of pullup and series resistors which allow all to coexist (at the expense of some excess current), but it's not trivial.

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