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R9 and R10 on Stellaris Launchpad LM4F120-removal

Tim Coddington
Intellectual 440 points

I have subject board and I'm reviewing documentation on using the Anaren Zigbee boosterpack.  According to Anaren's Boosterpack User's Manual, file: "A24530x24A_LPZ_Users_Manual.pdf", I can make modifications to use the I2C controller instead of default bit-banged method.  One of the steps involved requires me to "Remove R9 and R10 from the LaunchPad".    

I've been looking at the schematic and it's immediately apparent what R9 and R10 are doing.  Can someone help me understand what these resisters are for and what is the effect of removing them from the board circuit?  What's with the "0" value?  I have been using PD0 and PD1 (to which R9/R10 are connected) for I2c.  Are these external pullups?

Thanks

  • 0
    Guru 117855 points

    Tim Coddington said:
    what R9 and R10 are doing? 

    Many have shared that thought - and have been "amazed" (to be kind) by vendor answer.  Those 2 Rs are placed (we're told) to maintain compatibility with launchpads from an earlier - entirely different class of MCU!  Be not surprised - this from the gang who, "saw no evil" in "yanking" any/all Stellaris references - and then "leisurely" re-installing after multiple, proper, user/client "squawks!"  And - to make matters even worse - many of our clients called - yelled at us for vendor's "unannounced - and apparently poorly planned" launch of this "most necessary" brand re-format!

    These 0-ohm Rs directly connect GPIOs - not too common (nor safe - should both GPIO be outputs) a practice.  (but indeed - does have a time/place)

    Now a 0-ohm R cannot serve as a pull up - it does not easily allow any "known/standard" device to "pull it down!" (and if attempted - insure NYFD - and H20 pressure - ready/waiting/adequate... 2K - 10K far more standard for pull-up)

    So - check w/esteemed vendor - read the "boilerplate" (bottom of this page - thank this reporter for that...) and remove R9 & R10 if that is appropriate (and proper) for your application.

  • 0 in reply to cb1_mobile
    Prodigy 60 points

    Goodness. It took me the attempts to understand your answer! But it's good. Thank you.

  • 0 in reply to Wojciech Marcinek
    TI__Guru**** 244400 points
    Hello Wojceich,

    The resistors R9 and R10 were placed so that the boosterpack header be compatible with MSP430 booster packs that were available at the time. And as cb1 noted, it has been an issue for us as multiple drivers on this resistor short cause users not to realize what the issue is when the intended interfaces do not work.

    Regards
    Amit
  • 0 in reply to Wojciech Marcinek
    Guru 117855 points
    Simpler language attempt follows:

    Remove and then, "Throw those 2 "plague-istors" (R9, R10) as far away as you can!" (ideally into trash can and/or ocean...)
  • 0 in reply to cb1_mobile
    TI__Guru**** 244400 points
    Hello cb1,

    Or solder a mating connector with 2 wires, to allow for a reconnect, since there is no thru hold connector at the position.

    Regards
    Amit