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TLK100: reverse polarity

Hong Jieun
Prodigy 240 points
Part Number: TLK100

Hi I'm Jieun,

I have a question about PHY transceiver,TLK100.

According to the datasheet, Wrong polarity affects the 10B-T PHYs. 100B-TX is invulnerable to polarity problems because it uses MLT3 encoding.

 

Can I ask the reason? 

1.Why reverse polarity affects only 10B-T?

2.Why doesn't it matter if it's MLT-3 encoding?

regards,

  • 0
    TI__Mastermind 33635 points

    Hi Jieun,

    10BASE-T uses Manchester Encoding which is essentially an XOR of CLK and Data. Since our PHY's MDI is differential, whatever is on TRD_P is the exact opposite of TRD_M. You can imagine that if identifying polarify is very important when trying to decode here as if the PHY reads TRD_P as TRD_N, then the decoding would be messed up.

    10BASE-TX uses MLT-3 which uses a pattern of {0, +1, 0, -1} and cycles through that matter whenever the data on the rising edge of clock is a '1'. If this is '0', then the data will not move. In this signaling scheme, what matters is the event of a transition to detect a '1', not where the transition goes.

    Sincerely,

    Gerome