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TLK1501EVM: Read Data Only

Part Number: TLK1501EVM
Other Parts Discussed in Thread: TLK1501

Tool/software:

Hi, 

I am trying to read data through TLK1501EVM, we are receiving data through fiber optic cable and want to read RX[0:15] using logic analyzer.  

I can verify that Optical module is receiving signal by measuring SD pin out which measures 3.2V when fiber optic light is received. 

But not able to get any data. 

Please advise any troubleshooting methods or any jumper setting on J7 connector. 

Thanks.

  • Hi Anand,

    I'm assuming you are referring to the SD pin on header J7, connected to the laser module section of the EVM. Did you mount an optical module onto U2 on the EVM?

    I reviewed the EVM schematics and I don't see any on board connections between the laser module section and the TLK1501 device. You need to externally connect the module inputs/outputs to the TLK1501 inputs/outputs. Has this already been done?

    Once you have confirmed that the TLK1501 is properly receiving data, you can probe the RX_DV and RX_ER pins (header J6) to determine the type of data being received.

    Best,

    Lucas

  • Thanks Lucas.

    I'm a colleague of Anand. We got past the read issue. It was due to a problem with our fiber.

    This question remains.

    We want to read external fiber data but have yet to find a way to do so without feeding a GTX_Clk into the EVM, even though we don't need output from it. It would seem that the TLK1501 should be able to recover a clock from the receive stream without the aid of an external TX clock, but, so far, we can only clock RX data into a logic analyzer if we feed a EVM board a GTX_Clk signal.

    Is there a way for the TLK1501 to fully recover the RX clock without the aid of a GTX_Clk signal? If so, how? If not, how much mismatch is tolerable between the clock used for the EVM GTX_Clk and that which created the UUT TX stream which we're trying to read?

    Regards.

  • Hello CJ,

    Lucas is currently out of the office. He will be back early next week to help answer your follow-up questions. Thank you for your patience.

    Best,
    David

  • Hi CJ,

    My apologies for the delay.

    GTX_CLK input is required for TLK1501 operation, even if you only wish to use the receive data path (DINRXP/N to RD0-15). The GTX_CLK input is used as a reference clock for the internal PLL, which supports both transmit and receive functions. The receiver takes the high speed internal clock phases from the PLL and the clock/data recovery (CDR) function uses these clock phases to align a new clock phase to the center of the incoming data eye to make the recovered bit clock. Therefore, GTX_CLK is needed in order for the device RX to function. Without GTX_CLK the RX data will not be recovered.

    Since the GTX_CLK input is only used as a reference clock for the receive path, it does not need to be synchronous to the input data stream. GTX_CLK frequency does need to be equivalent to the input data stream's rate divided by 20. For example, if the input data stream is 1.5Gbps, GTX_CLK needs to be 75MHz. The max tolerance of GTX_CLK is +/-100ppm.

    Best,

    Lucas

  • NP. Thanks for confirming and providing the additional information. Interesting your direction of a 20x clock...We're leveraging off of an existing design which has appeared to work for years, however I'm seeing a very small amount of data glitching in our specific setup/application. If we can't resolve by sharpening our clock, we'll investigate your 20x recommendation.

    Thank you again.

  • Hi CJ,

    The reasoning is because GTX_CLK is also used to sample TXD0-15 inputs on the rising edge. So GTX_CLK needs to have frequency R which matches the data rate of the parallel side of the TLK. These 16 bits of parallel data are encoded and serialized into 20-bit words on the serial side of the TLK, therefore the serial side of the device operates at data rate 20*R. The GTX_CLK is actually multiplied by a factor of 10 to create the internal bit clock, but the serial data is clocked on the rising and falling edges to achieve a data rate of 20*R.

    Best,

    Lucas