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C6678 EMU Pins

Richard Marsh
Intellectual 760 points

Hi,

The generic "Emulation & Trace Headers (spru655g)" document says that the EMU termination resistors should be placed close to the DSP - page 21, note A.

Yet the Advantech EVM and Lyrtech EVM both show the 10R EMU termination resistors next to the 60pin connector.

What should we follow?  The non Keystone specific sprug655g or the reference designs?

Cheers,

Richard

  • 0
    TI__Mastermind 30825 points

    Richard,

    The note in the guidelines say

    A To select EMU and TDO series termination resistor values, see Section 10. The EMU and TDO series termination
    values should be placed within 0.5" of the device with total routing length not to exceed 3".

    I'm not 100% certain if this is exceeded on the EVMs or not, but the goal is to have them as close as realistically possible. 

    The guidelines always supercede EVMs, which while often are used as reference designs are not intended to be reference designs.  EVMs are developed prior to device characterization and there may be things that differ because of our increased understanding from how it was implemented on an EVM vs how we recommend customers implement it.

    Best Regards,

    Chad

  • 0
    TI__Expert 8055 points

    Richard,

    I recommend following SPRU655g.  There is nothing specific about the 6678 that should make this any different.  I suspect that the EVMs are slightly out of spec with SPRU655, but are probably within a tolerance that this still works.

    I checked SPRU655g, and the note that you refer to says :

    A: To select EMU and TDO series termination resistor values, see Section 10. The EMU and TDO series termination
    values should be placed within 0.5" of the device with total routing length not to exceed 3".

    It's hard to tell from simply looking at the Advantech EVM, bit it's possible that the EVM is actually meeting this requirement.  I believe the EMU pins are right near the top left  edge of the CPU (when looking at the board with the power cable at the top).  It's not much more than a half an inch to the emulation header, and well less than 3 inches.  The termination resistors do look like they're right next to the EMU header. 

    Regards,

    Dan