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DS92LX1621/2 cml-signal

Marc Koltermann
Prodigy 40 points
Other Parts Discussed in Thread: DS92LX1621, LX16EVK01

Hello,

I tried to measure the cml-signal between the serializer and deserializer. I have got a squarewave signal which is modulated on another signal (see attached pictures) 

Is this carrier signal the signal of the backchannel or is it a unwanted signal or something else? Is it possible to deaktivate the backchannel?

  • 0
    TI__Expert 7395 points

    Hi Marc,

    The DS92LX1621/2 chipset is a bidirectional interface that uses Channel-Link III signaling; which transfers both high speed data and control data over the single diff pair. If you monitor the differential lines on the DIN/ROUT pins when the devices are connected together, you will observe the superposition and mixing of both the high speed forward and back channel signals (full duplex). Hence, you will be unable to monitor the eye diagram. To measure the eye opening on Deserializer, there is a mode that provides a loop through output of the recovered forward channel (without back channel) after EQ equalization and prior to the CDR block. The loop through driver is available on RES pin 32 (CMLOUTP) and pin 33 (CMLOUTN). To enable the CMLOUT pins to measure the high speed eye opening, program register address 0x3F’h bit 4 to 0 (CMLOUT=enabled).

    Dac Tran

    SVA / APPS

  • 0 in reply to Dac Tran
    Prodigy 40 points

    Hi Dac,

    I tried this on the evalkit LX16EVK01. The register address 0x3F have the value 0001 0000, so I changed it to 0000 0000. The pins 32 and 33 are carried out to P1 (open USB) pin 2 and 3, but there is no signal. I read out the full adress again and it changed to some random configuration and I had a signal. After disconnect the evalkit from powersupply the register changed to its default values and I didnt had a signal again. Are there some other addresses that I have to change?

    There went something wrong, now I have a signal. Is it possible to keep the address at this value, even after disconnecting the kit from the powersupply?

  • 0 in reply to Marc Koltermann
    TI__Expert 7395 points

    Hi Marc,

    If you are using the LX16EVK01 EVM boards, you can probe pins 2,3 on the P1 connector on Deserializer board. The default value of register 0x3F = 0x10. You should only need to set 0x3F bit[4]=0 to enable the CMLOUT loop-through driver. Make sure the Deserializer is a Locked (JP5 = High) to the Serializer in order to see the signal waveform. Also note the signal will be differential output. 

    Dac Tran

    SVA / APPS