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DM365 Hardware questions

Doug Goss
Intellectual 290 points

1. I noticed that on the Spectrum Digital EVM schematics that on the 24MHz and RTC oscillator the other side of the crystal caps, along with the pin on the DM365, are not connected to a board ground. The datasheet says that these pins (L2 and H2) are oscillator ground. Does this mean that the DM365 ties them to ground and that i should not?

 

2. On a few of our boards, we will have two DM365s (one for encode and one for decode). On these boards, can we daisy chain the JTAG connector to the two parts? If we do this, will there be a method for controlling which part we are communicating with?

 

3. The audio codec on the Spectrum Digital EVM has a 27MHz Osc feeding the audio codec. Why was that frequency chosen? It doesn't seem to fit into the desired frequencies for the popular audio modes. What am i missing?

  • 0
    TI__Expert 5955 points

    Hi Doug,

    1. Do not connect to other grounds - only to the crystal capacitors as on EVM ground is suplied by the VSS pins.

    2. Depending on the distance on the jtag chain you should consider buffers, the TDO of one should go to the TDI of the next part and TDO of the 2nd part back to the emulator. It is recommended to use 2 jtag connectors and then a buffer to chain them together with a jumper enable than way you can always separate the chain. The order of the configuration of the JTAG chain in setting up your debugger should control which part you are talking to. Note that TI CCS3.x and CCS4.x debugger allow this type of configuration.

    3. I agree with you - the 27Mhz is not the most desirable frequency but does the job, it was picked by the TI EVM spec owner at the time. 

    Thanks.

    Tai

  • 0 in reply to Tai Nguyen
    TI__Guru**** 171094 points

    Tai, Doug,

    The reply to this thread is located at:

    http://e2e.ti.com/support/dsp/davinci_digital_media_processors/f/100/t/53561.aspx

    Cheers,

    Rafael