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SN75DP159: DP159 SNOOP mode

Terry Wu
Expert 1680 points
Part Number: SN75DP159

Hello Sir,

Need your suggestion !

Now we use external level shifter IC for DDC 1.8V to 5V .

We connect 5V DDC into DP159 SCL_SNK and SDA_SNK pin and HDMI output connector .

That the DDC bus will  NACT . If we disconnect DDC from DP159 SCL_SNK and SDA_SNK , that DDC will ACT and display OK !

Is CLK stretch is must for this external level shifter ?

How to treat SCL_SRC  and SDA_SRC pin ?  Short to GND ?

Many thanks !

  • 0
    TI__Guru 60870 points
    Hi Terry,

    SCL_SRC and SDA_SRC should be shorted to ground to prevent the DP159 from interpreting noise as I2C traffic and erroneously holding the bus when in snoop mode. The DP159 should have no impact on DDC if it is implemented in snoop mode (only connected to SCL_SNK and SDA_SNK). Can you provide a partial schematic? Is the DP159 powered on when this behavior occurs?

    Regards,
    JMMN
  • 0 in reply to JMMN
    Expert 1680 points

    Hello JMMN,

    After short SCL_SRC and SDA_SRC . Its OK!

    Is the "Clock stretching" function necessary or not ?

    Many thanks !

  • 0 in reply to Terry Wu
    TI__Guru 60870 points
    If the DDC is implemented in snoop mode, clock stretching support is not needed by the DP159.

    Regards,
    JMMN