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SN75DP159: SN75DP159 TX_TERM_CTL & SWAP pin

Terry Wu
Expert 1680 points
Part Number: SN75DP159
Other Parts Discussed in Thread: TMDS181,

Dear Sirs

48 pin version have this two pins but 40 pin version without it.

I want to double confirm this two default feature in 40 pin version

- SWAP pin : Check  register 0x09 . Looks like default is no swap ,right ?

- TX_TERM_CTL pin : Check register 0x0b . Default is No termination ???  What's it mean ? Auto setting terminator resistor ?

Many thanks !

  • 0
    TI__Guru 60865 points

    Hi Terry,

    Correct, there is no SWAP capability using pin configuration - it can be implemented via register settings with SDA_CTL/SCL_CTL. TX_TERM_CTL will default to automatic mode, where it changes terminations based on the data rate. TX_TERM_CTL can also be set via register settings with SDA_CTL/SCL_CTL.

    Regards,
    JMMN

  • 0 in reply to JMMN
    Expert 1680 points

    Hello JMMN,

    I got it and many thanks your quickly feedback. TKS !

  • 0 in reply to JMMN
    Expert 1680 points

    Hello JIMM,

    Sorry that I have similar question about TMDS181 TX_TERM_CTL pin.

    e2e.ti.com/.../2228764

    Will TMDS181 be different with DP159 ?  TKS !

  • 0 in reply to Terry Wu
    TI__Mastermind 23815 points
    Hi Terry,

    The TMDS181 is only available in one 48-pin package, the control of TX_TERM_CTL feature is the same for DP159RGZ and TMDS181.

    Regards
  • 0 in reply to Moises Garcia
    Expert 1680 points

    Hello Sir,

    Sorry my description not clear ~

    I mean when TMDS181 use I2C control mode.

    TX_TERM_CTL default setting is No termination at register 0x0b . Is this default "No termination" is "Automatically selects the impedance" ??

    Same as SN75DP159 ?

    TKS~

  • 0 in reply to Terry Wu
    TI__Mastermind 23815 points
    Hi Terry,

    Yes, the behavior is the same, it has the same description in the register table.
    In I2C, the default is no termination and there is no automatic Tx termination selection, it has to be selected accordingly to TMDS_CLOCK_RATIO_STATUS.

    Regards
  • 0 in reply to Moises Garcia
    Expert 1680 points
    Hello Garcia,
    May I double confirm will the 40 pin version SN75DP159 .Due to there's no TX_TERM_CTL pin . I can see the deafult is "No termination" at register 0x0b .
    It is same as TMDS181 and 48 pin version SN75DP159 "no automatic Tx termination selection" and need to read CLOCK_RATIO_STATUS to determine termination resistor .
    Or its "automatic Tx termination selection" .

    Actually we use 40 pin version and want to use PIN straping not i2c control. So we need to make sure default is workable for this removed pin.
    Many thanks ~
  • 0 in reply to Terry Wu
    TI__Mastermind 23815 points
    Hi Terry,

    The DP159 has two modes of operation, I2C or GPIO. In GPIO mode, there is automatic Tx configuration and there are two packages DP159RGZ and DP159RSB.
    The DP159RSB has no external TX_TERM_CTL pin, it is left NC internally. So, in GPIO mode the DP159RSB is configured for automatic Tx termination selection, and this can't be changed in GPIO mode.

    DP159RGZ and TMDS181 have the same behavior in both GPIO and I2C mode.
    In GPIO mode, both have automatic Tx selection.
    In I2C mode, both lack of automatic Tx selection.

    Regards
  • 0 in reply to Moises Garcia
    Expert 1680 points

    Hello Garcia,

    Many thanks your detail description !

  • 0 in reply to Moises Garcia
    Expert 1680 points

    Hello Garcia,

    "DP159RSB has no external TX_TERM_CTL pin , So, in GPIO mode the DP159RSB is configured for automatic Tx termination selection"

    May I double confirm if we don't use DP159 level shift for SCL_SRC & SDA_SRC & SCL_SNK & SDA_SNK ( left this four pins NC because of 1.8V SCL & SDA signal )

    Will this automatic Tx termination still workable ?

    Whether we need to connect SCL_SNK & SDA_SNK for "DDC Snoop Block"

     

    Many thanks !

     

  • 0 in reply to Terry Wu
    TI__Mastermind 23815 points

    Hi Terry,

    When the DP159RSB is in GPIO mode, the Tx termination is selected from data rate and TMDS_CLK_RATIO, the TMDS clock ratio is monitored from DDC.

    The DP159 implements I2C clock stretching, if you face interoperability issues from clock stretching we recommend using DDC snoop mode.

    Long story short, for automatic Tx termination you need at least DDC snoop mode, then, you will need a level shifter from 5V(or 3.3V if there is no I2C clock stretching interoperability issues)

    Regards

  • 0 in reply to Moises Garcia
    Expert 1680 points
    Hi Garcia,
    Many thanks your quickly reply !

    Due to CPU's DDC is 1.8V could not use DP159 level shift from 3.3V to 5V .
    In other words, will the TMDS clock ratio function fail if we use external level shift IC for 1.8V DDC to 5V DDC ?

    Regards
  • 0 in reply to Terry Wu
    TI__Mastermind 23815 points
    Hi Terry,

    You will need a level shifter because 5V is the requirement for HDMI.
    So you have a couple options,
    1.8V to 3.3V -> DP159 -> just add pull-ups to 5V; make sure there are no interoperability issues from I2c clock stretching.
    1.8V to 5V (DP159 DDC snoop mode)

    The level shifters are supposed to be transparent to DDC.

    Regards
  • 0 in reply to Moises Garcia
    Expert 1680 points
    Hello Garcia,
    Just one more question :
    1.8V to 3.3V -> DP159 -> just add pull-ups to 5V; make sure there are no interoperability issues from I2c clock stretching. <= Its OK!
    1.8V to 5V (DP159 DDC snoop mode) <= Do you mean level shift IC's 5V SCL/SDA side connect to DP159's SCL/SDA_SNK side (5V) ??
    Many thanks ~
  • 0 in reply to Terry Wu
    TI__Mastermind 23815 points
    Hi Terry,

    In the second option where a 1.8V to 5V level shifter is used, the 5V output of the level shifter will connect to SCL_SNK/SDA_SNK and HDMI connector using 2k pull-ups. This configuration is DDC snoop mode, you still have to connect SCL_SRC/SDA_SRC to GND.

    Regards