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Original question:

SN65DP149: DDC clock operation

SN65DP149: Does not copy I2C_SRC to I2C_SNK at startup - unless cable is disconnected and reconnected

Steven VALSESIA
Prodigy 30 points
Part Number: SN65DP149

Hi,

I have the exact same problem as the refering question using the SN65DP149.

The SN65DP149 is connected to a DDI port of a ComExpress type 6.

+/- 5s after booting, when the DVI cable (desktop screen) is already connected, an I2C trame is sent from the ComExpress (I2C SRC = I2C 3V3) but not copied into I2C SNK (I2C 5V) :

When the cable is disconnected and reconnected, it works (SDA SRC is in 2nd position in this one to simplify debugging) :

The schematics is derived from the datasheet :

I've tried to force the HDP SRC to HIGH, did not change anything.

Does anyone have any idea?

Thanks !

  • 0
    Prodigy 30 points

    The last answer of the "related question" was to increase the "OE input" capacitor.
    I increased from 100nF to 220nF and it's better.

    I think I need more like 470nF, or to remove the pull-up / 10k resistor.

    Removing the pull-up on OE fixed the problem.