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LOL signal of 8T49N241 frequency translator in synthesis mode & DBITM setting

JeDi

Dear all,

I have a question regarding the LOL signal of the the 8T49N241 frequency translator which can be output via GPIO3. When using the device in synthesis/free-run mode without using the digital PLL, does this signal reflect the lock status of the analog PLL? The datasheet clearly states that the signal reflects the signal of the digital PLL but what confuses me is that for the Xilinx ZCU104 board, the signal is directly routed to the FPGA fabric and used as the "tx_refclk_rdy" signal for the video phy controller. When only using the TX capability, the 8T49N241 device is configured in free-run mode and, according to the datasheet, should therefore not generate a LOL signal.

My second question is about the DBITM setting in register 0x0069. According to the datasheet, this bit should have a default value of 0. In my case, it is 1 after reset. What does this setting (as well as VCOMAN and DBIT) do?

Best regards,

Jelle

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  • 0 in reply to JeDi

    The configuration that you provided in the form of register values, are these values what the you are writing to the device or reading from the device? Or is it both, i.e. they write it and read back identical values?

    I took this register sequence and manually set the register values based on the provided values. 

    The resultant configuration raises several errors in the Timing Commander GUI.

    1. GPIO3 output function = 0x4, which is a reserved value. It is possible that the customer configuration was created using a older personality in which this value was not reserved. I would need the TCS file to confirm this

    2. The VCO frequency (4744.39678125MHz) violates the valid range of 2999.997MHz to 4000.004MHz.

    We compared the register contents of 8T49N241-998 against the register contents provided by you. There are 32 registers (about 25% of registers) that have differing values between the configurations. Of these 32 registers are the registers controlling the VCO frequency, the GPIO3 output function, DBITM, VCO_MAN, and DBIT. Note, DBITM = 0 in 8T49N241-998, so it is this sequence is setting it to 1.

    With this many differing registers and the dash code number of 998, we can only assume that you are trying to program only select registers. This is typically okay, however, they would need to ensure the written values are valid (i.e. VCO frequency and GPIO function).

    Are you programming the device yourselves?

    1. If yes, what is it that they are trying to achieve with their configuration. We can help provide a correct write sequence.

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