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[FAQ] What to do if the TM4C129 ROM boot loader is not functional on custom hardware

Ralph Jacobi
Guru*** 135355 points

Other Parts Discussed in Thread: EK-TM4C1294XL, TM4C1294KCPDT, TM4C1294NCPDT, TM4C1294NCZAD, TM4C1299KCZAD, TM4C1299NCZAD, TM4C129EKCPDT, TM4C129ENCPDT, TM4C129ENCZAD, TM4C129LNCZAD, TM4C129XKCZAD, TM4C129XNCZAD

Issue: Trying to invoke the ROM boot loader does not work as expected even with identical software being used from evaluating on EK-TM4C1294XL LaunchPad.

The part used is one of the following:

  • TM4C1294KCPDT
  • TM4C1294NCPDT
  • TM4C1294NCZAD
  • TM4C1299KCZAD
  • TM4C1299NCZAD
  • TM4C129EKCPDT
  • TM4C129ENCPDT
  • TM4C129ENCZAD
  • TM4C129LNCZAD
  • TM4C129XKCZAD
  • TM4C129XNCZAD
  • 0
    TI__Guru*** 135355 points

    Likely Root Cause: Errata Item ETH#03: http://www.ti.com/lit/spmz850

    Solution: As per the datasheet the acceptable practice for Ethernet PHY enabled parts is a no connect (NC) to the RBIAS pin if on-chip PHY is not used. However, the ROM Boot Loaders enable the Ethernet PHY when the Flash is erased for Ethernet PHY parts which causes the ROM Boot Loader to fail. Also if a 25MHz crystal is used without RBIAS resistor, then JTAG may not work.

    A RBIAS resistor is required even if the application does not require the Ethernet PHY. In this case, a 4.7KOhm 10% tolerance resistor can be used in place of 4.87KOhm 1% tolerance resistor between the RBIAS pin and GND.