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proper termination of RO pin on DS90LV019

Nikoo Naeemi
Prodigy 180 points
Other Parts Discussed in Thread: DS90LV019

Hello,

I want to use DS90LV019 as a transceiver between a LVDS device and ATXmega USART, which is a 3.3V device. I have enabled the Xmega Pull-Up resistor on RX pin, but still receiving unexpected data due to noise or crosstalk. Will be great if you can inform me about any required passive components on Ro pin. 

Thank you,

Nikoo

  • 0
    TI__Mastermind 43795 points

    Nikoo,

    There are no required passive components on the Rout pin.  I do not understand your comment about the "RX" pin, which pin are you referring to?  If you could attach a schematic and scope waveforms of the noise and valid data signals it would be helpful.

    Regards,

    Lee

  • 0 in reply to Lee Sledjeski
    Prodigy 180 points

    Hi Lee,

    Ro pin on the DS90LV019 is connected to the RX pin of the Xmega USART. I increased the terminating resistor between Ri+ and Ri- and it helped a bit, but still receive some error bytes. The point is that I do not have any issue, connecting RO to FTDI 3.3V RS-232 to USB cable; I do not receive any extra/unexpected data on COM port. I assume that the LOW level thresholds are different, and Xmega may consider a slightly higher voltage as Logic zero.


    Cheers,

    Nikoo

  • 0 in reply to Nikoo Naeemi
    TI__Mastermind 43795 points

    Nikoo,

    Ports on the Atmel Xmega device seem to follow standard JEDEC convention and logic levels.  I did not see any pins labeled TXD and RXD in the datasheet.  The error source is likely in the connections on the differential side?  Are you connecting RI+/- and DO+/- together? Are the driver and receiver of the DS90LV019 always enabled?

    Regards,

    Lee

  • 0 in reply to Lee Sledjeski
    Prodigy 180 points

    Hi Lee,

    There are two USARTS on ports C, D and E of the Microcontroller that I am using, each USART has one pair of TX and RX pins. I am not connecting RI+/- and DO+/- together, they are connected to the LVDS pairs of the serial communication on a Camera Link interface.  I agree that there are some noise at the differential stage, as changing the terminating resistor reduces the noise level. But it is weird that the same interface works with the RS-232 FTDI converter and is not showing any faulty data. But when it is connected to the Microcontroller it starts sending faulty data.

    Hope this clarify the confusions.

    Thank you,

    Nikoo 

  • 0 in reply to Nikoo Naeemi
    TI__Mastermind 43795 points

    Hi Nikoo,

    Thanks for the additional information.  A camera link interface can run at many 100's of MHz.  This is faster than the DS90LV019 can respond.  Do you know the datarate for this interface?

    Regards,

    Lee 

  • 0 in reply to Lee Sledjeski
    Prodigy 180 points

    Hello Lee,

    The baud rate is 115200, and the interface does not have any issue in transmitting data, I have the noise issue at the receiver side.

    Cheers,

    Nikoo 

  • 0 in reply to Nikoo Naeemi
    TI__Mastermind 43795 points

    Can you measure the data at the LV019 Rx with an oscilloscope and post the picture?

    Thanks,

    Lee