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TM4C1294NCPDT: JTAG connection

Nishitha Chandrasekar
Intellectual 700 points
Part Number: TM4C1294NCPDT

Hi,

I am going to design my own PCB board using TM4C1294NCPDT controller. I have gone through system design guidelines for TM4C129x and TM4C12x Devices Over JTAG Interface for JTAG connection.I am choosing cortex ARM 10pin debug connector. When this micro controller has default internal pull up resistor for TCK, TMS, TDI and TDO means whether this connection is sufficient for JTAG connection.   

  • 0
    Guru 117855 points

    Those internal, MCU resistors are (very) high in value.   (~50K+)

    While they (have) worked - the signal edges & potential for signal reflection - renders them,  "sub-optimal."     Our firm has found - over many years - that external resistors (~10K) - installed very close to the MCU's JTAG/SWD pins - prove FAR more robust.

    Should you employ the Forum Search Box (atop this page) - you will note (many) difficulties in establishing JTAG connection.     Often - such is noted via the (saving) of those,  "enhanced signaling,"  external resistors...     Risk-Reward (strongly) argues for their deployment...

  • 0 in reply to cb1_mobile
    TI__Guru**** 175276 points
    Hi Nishitha,
    Cb1 is correct. Please add the external pullup resistors as shown in the guideline for proper operations.
  • 0 in reply to Charles Tsai
    Intellectual 700 points

    Hi Sir,

    Sorry, I have a doubt what about that R13,R14, R15 and R16 - 33ohm resistor. Whether it is required or not ??

  • 0 in reply to Nishitha Chandrasekar
    Guru 117855 points

    Squelch you doubt - those resistors provide a useful, "Safety Factor" - protecting the critical JTAG inputs from (reasonable) transients - while reducing the impact of "noise."    The "cost/size" adder of 4 smt resistors makes their implementation a "No brainer."

    Client-users must ALWAYS "factor in" the costs of  "Board Failure" - and/or  "Difficulty in JTAG Programming/Debug" - which (unfortunately) is NOT "unknown" here...     Those resistors ADD robustness - case closed!