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MSP430FR2633: Do SWDIO and SWCLK pins require external pull up resistors?

Expert 1600 points
Part Number: MSP430FR2633


I built a few boards having MSP430FR2633 MCU, I noticed the SWD interface is not very stable during programming FW.

I didn't add pull-ups on the PCB as I assumed the programmer (MSP430F5529LP) can pull these pins up if needed. 

Do I need to add pull-ups on the PCB to improve the stability of the SWD interface?

  • Hi,

    I think your means should SBWCLK & SBWDIO.

    It is also TEST and RST pin, you need pull up a resistor in RST pin. for another pin, keep float is OK.

    PS: the Cap in RST pin need < 2.7nf, we recommend 1nf.

    Thanks!

    Best Regards

    Johnson

  • Hi,

    Thanks Johnson, I have RST PU and the Cap.

    100KOhm is good for SBW pins?

    Thanks

  • FET programmer  can pull up/down this pins if needed, so it should handle it without any issue. Don't know about FR2633 (you can find this info in datasheet) but MSP430F5xx/6xx devices also have internal pull-up on RESET pin (and all MSP430 devices have internal pull-down on TEST pin), so external is not needed. Capacitor on RESET pin is related to safe start up on older MSP430 members, not for new one (like FRAM)  and  for SBW interface it is only disturbing factor. SBW working better without it.

    So I guess that your problem (not stable during programing) is somewhere else. Try to use shortest possible cables/wires between your LP FET master and target devices.

  • Thanks, 

    I have 2 boards; both with no PUs; one is working fine, 1 needs several trials to get it running.

    With a Logic Analyzer, I see the SWDIO pins held at low; only when I manually connect it to a high and let the programmer take over, it works.

    I think adding a PU might be safer, but I wish I root cause this issue and better understand it

  • How power supply is connected / shared between SBW master device and target device board? Maybe there is something wrong with device  power supply. Can problematic board execute program after firmware update, when it is released / disconnected (physically) from master device, as a standalone?

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