SN65DP159: SN65DP159 application query

Hi,

Question#1: What's the function of active DDC block? whether the pins of SCL_SRC, SDA_SRC must connect to SOC side(source side) and SCL_SNK, SDA_SNK must connect to sink side?

*** DDC is the bus between a source such as a GPU and a sink such as a monitor that enables the monitor to communicate its supported video resolution to the GPU and that enable the GPU to adjust monitor parameters, such as brightness and contrast.

SDA/SCL_SNK must be connected to the sink side. For SDA_SRC and SCL_SRC, it depends on GPU

• If GPU supports 3.3V signaling and clock stretching, then you connect SDA_SRC and SCL_SRC to GPU
• If GPU does not support 3.3V signaling or clock stretching, then you have to use external level shifter and implement the DP159 DDC snooping option
  • The SNx5DP159 uses clock stretching for DDC transactions. As there are sources and sinks that do no perform this function correctly a system may not work correctly as DDC transactions are incorrectly transmitted/received. To overcome this a snoop configuration can be implemented where the SDA/SCL from the source is connected directly to the SDA/SCL sink. The SNx5DP159 will need its SDA_SNK and SCL_SNK pins connected to this link in order to the SNx5DP159 to configure the TMDS_CLOCK_RATIO_STATUS bit. Care must be taken when this configuration is being implemented as the voltage levels for DDC between the source and sink may be different, 3.3 V vs 5 V.

Question#2: In the reference design of SN65DP159, the pull-up resistors of SCL_SRC，SDA_SRC，SCL_SNK，SDA_SNK，SCL_CTL，SDA_CTL are 2kohm, can I change these pull-up resistors to 2.2kohm?

*** You can use 2.2k on SDA/SCL_SNK/SRC and SDA/SCL_CTL, but the actual pullup resistor on SDA/SCL_CTL may change depending on the number of I2C devices on the I2C bus.

Thanks

David