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SN65DP159: Is there any problem connecting SCL_SRC to SCL_CTL and SDA_SRC to SDA_CTL?

Andrew McBain
Prodigy 190 points
Part Number: SN65DP159

Tool/software:

On the SN65DP159RGZ, is there are two I2C busses one for the DDC ROM that would be on the display (SCL_SRC, SDA_SRC) and another one for accessing the device registers in the SN65DP159RGZ (SCL_CTL, and SDA_CTL).

Assuming that we are using the same supply voltage for both sets of I2C busses, is there any potential problems connecting them together so that we can access both the ROM and device registers on the same I2C bus?

SCL_SRC connects to SCL_CTL

SDA_SRC connects to SDA_CTL

The ROM on an HDMI bus is typically at device address 0x50 and the SN65DP159RGZ is at address 0xB6, 0xB8, 0xBA, or 0xBC, so there should be no conflict.

Is there anything I am missing?

  • 0
    TI__Mastermind 40260 points

    Hi Andrew,

    The SDA/SCL SRC pins are used for DDC communication between the HDMI sink and source, and the CTL is to program the device itself. Its best to keep these independent of each other.

    Can you share a schematic?

  • 0 in reply to Vishesh Pithadiya
    Prodigy 190 points

    Unfortunately, I can't share a schematic.

    Assuming both I2C interfaces behave normally, I wouldn't think it shouldn't be any different than putting two I2C devices on the same bus.

    Is there a reason they should be kept separate?

    If the concern is just software drivers not behaving properly, we can work around that since we can write our own drivers if needed.

    I am mainly concerned with respect to any electrical issues like the I2C bus locking up or similar issues.

  • +1 in reply to Andrew McBain
    TI__Mastermind 40260 points

    Hi Andrew,

    The reason I recommend separating the two is because the SDA/SCL SRC pins support clock stretching. This may not be supported by the I2C controller used to program the device via the I2C CTL pins. This could be a case where the I2C bus may hang.

    Additionally all the I2C lines on the DP159 are open drain, so if a monitor plugged in is push pull this may hold the control lines and cause the bus to lock up. Having a push pull monitor on just the SDA/SCL SRC pins is ok.

  • 0 in reply to Vishesh Pithadiya
    Prodigy 190 points

    Well, those are potentially good reasons.  In any case, when I looked into it further, we have multiple HDMI ports on this product, so we can't share the I2C bus.  Because if we did that the DDC ROMs on the monitors (all having the same I2C address) would be in conflict.