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SN65LV1224B keeps locking and unlocking

Other Parts Discussed in Thread: SN65LV1224B

I am using the SN65LV1224B chip on the SN65LV1224BEVM board to decode LVDS data coming from a custom board with an FPGA on it. I am using a 27MHz oscillator has the REFCLK input. My LVDS data is being transmitted at serial rate of 128.4MHz(/12 = 10.7MHz parallel) . The deserializer Lock pin never goes low and the RCLK output doesn't show any clk output. I have tried sending the actual data I want to send, 0X000, 0x3ff, etc. I can see my LVDS signal on a scope and I am correctly sending the start and stop bits. I also tried a 10.519MHz clk as the REFCLK input and the chip would Lock for a few hundred ns and the unlock over and over. When the lock pin was low the RCLK out was at about 10.5MHz not the 128.4MHz clk the LVDS data was being transmitted at. Any help to resolve this issue would be appreciated.

What is the relationship between REFCLK input frequency and the frequency of the serial data. Does the REFCLK just need to be between 10MHz and 66MHz and it doesn't matter what the serial data frequency is?

  • Hi Elena,

    The REFCLK needs to be within +/1% of the TCLK for that device. If that is a problem for you, you could consider the DS92LV1224 which has a slightly better tolerance of +/-5%.

    Note: TCLK x 12 = serial line rate.

    Mike Wolfe

    DPS APPS / SVA

  • Hi Elena,


    I agree with Mike that you have a clocking issue. The REFCLK needs to be within +/-100ppm (200ppm) of the incoming data stream. What is the reference clock source to your FPGA? 10.7MHz?

    Also, one of two things needs to happen to achieve lock:

    1. The synch pin on the SN65LV1023A needs to be toggled forcing the serializer to send 111111000000, allowing for only ONE 10 transition within the first twelve bit frame.
    2. The input/start-up pattern needs to avoid having a 01 transition to start with because the SN65LB1224B is looking for 10 to lock. It will see 1010 and sit idle not knowing what pattern to lock to.

    Are one of these things happening?