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DS90C241/DS90C124

Other Parts Discussed in Thread: DS90C124, DS90C241

Hello,

This is with reference to DS90C241/DS90C124.. wanted to know the reason as to why the PLL in serialiser (DS90C241) doesn't get locked to TCLK when VCC is powered due to which I don't get output at serialiser. Similar problem arises with deserialiser (DS90C124). Have shorted TCLK of DS90C241 to RCLK of DS90C124. Is there any problem in this? Please reply

  • Hi Soniya,

    It is not typical to have the recovered RCLK output tied to the TCLK input.  Can you upload a schematic showing the DS90C241/DS90C124 devices? 

    What is the TCLK frequency?  It should be between 5-35 MHz. 

    Is TPWDNB = Logic 1 (High) ?

    Is RPWDNB = Logic 1 (High) ?

    Regards,

    Lee

  •  Hello,

    Thanks for the reply..

    TPWDNB= logic 1

    RPWDNB=logic 1

    TCLK frequency is between 5-35 MHz.

    But m still not getting the output at DS90C241 and DS90C124.

    Are these components not compatible with the signals from USB, RS232, RS485 and Ethernet? as these signals are input to serialiser .

     

    Thanks

  • Hi,

    I would not generally associate these devices with USB, RS232, and Ethernet applications.  Looking at the schematic, the Control and Data inputs all seem correct and follow datasheet guidelines.  The Clock input looks like it is drawn as an "output" on the schematic.  The input Clock is very important to the operation of the DS90C241, what is the frequency of the input clock?  What are the logic levels of the input clock?  The input clock signal should have monotonic edges and a typical amplitude of 3.3V.

    Regards,

    Lee  

  • Hi,

    I had connected Clk of DS90C241 to clk of DS90C124 and applied frequency to TCLK between 5-12 MHz, with 1V,also tried with 3.3 V. But still m not able to get the output.. Is it because of the signals from USB, RS232, RS485 and Ethernet provided as input?
  • Hi,

    I do not think you have the DS90C241 and DS90C124 connected correctly.  Do not connect the clocks together.

    Start with just the DS90C241 and connect a 3.3V clock to the TCLK input.  Once a valid clock is available on the DS90C241 input, the serializer should be able to lock to it and output the serial data. 

    Verify with an oscilloscope that the frequency and voltage levels of the clock meet the datasheet specification at the TCLK input.

    Tell me more about the USB,RS232,RS485, and Ethernet signals you are sending into the DS90C241 device. What are the voltage levels of these signals and how are they related to the clock signal?

     

    Regards,

    Lee

  • Hi,

    I disconnected both the clocks and gave input clock to DS90C241. But still the signal does not get locked.

    Voltage values of USB and RS232 signal is 5V. Didn't try with RS485 and Ethernet signals yet as it was giving problems with this.

    I feel there is compatibility issue between the data rates of signals from USB and RS232 and DS90C241. Could that be the reason for signal not getting locked with TCLK in DS90C241.
  • In a typical application the input signals are indeed synchronous with the TCLK input.  The voltage level of these inputs should be limited to values between GND and +3.3V.  With a clean clock at the TCLK input the DS90C241 should lock and you will see a serial signal on the DOUT pins.

    Can you measure the TCLK input with an oscilloscope?

    what are you using to generate the TCLK signal?

    Regards,

    Lee 

  • Hello,

    TCLK input is been set to 3.3 V and frequency of 5MHz.For now I am giving it from frequency generator.

    Since input to DS90C241 is more than 3.3 V, could that be the reason that there is locking problem in DS90C241?
  • Hi Soniya,

    The DS90C241 was not designed to accept USB, RS232 and RS485 signals. From the datasheet the absolute maximum input voltage that can be supplied to an LVCMOS input pin on the DS90C241 is Vcc + 0.3V, which should be no greater than 3.9V.

    By supplying a 5V signal to the device you have violated the absolute maximum ratings and may have physically damaged the device.

    If you are trying to create a data pipe that will haul USB, RS232 and RS485 over a single twisted pair I recommend you use and FPGA. Inside the FPGA you can create your own mux/serialization structure to pipe these three different protocols together.


    Mike Wolfe
    DPS APPS / SVA
  • Hi,

    Thanks.. But could you suggest a way to reduce the voltage of 5 v from USB ,RS232 and RS485 TO 3.3V so that it can be applied to input of DS90C241, as I am running short of time to start with FPGA. If there could be some modifications possible such as including interfacing IC between these two levels?
  • The logic level translation from 5V to 3.3V can be accomplished with many different logic devices.  Here is a good example, SN74LVC4245A

     

  • Soniya,

    Just to be clear you will need to work with a new device, one that you have not yet electrically over-stressed with 5V signals.

    The DS90C241 has a parallel clock input range of 5 to 35 MHz, the device can only accept data inputs which toggle slower than 35 MHz or 17.5 Mbps. This means that if you strip away the half duplex nature of USB and force it to stream constantly in one direction, then you will only be able to support USB1.0 or 1.1 speeds.

    Please confirm which USB spec you are trying to use.

    Also, as noted previously you will need to provide the input TCLK from either the same clock domain as your highest speed data or ensure that the TCLK is much much faster than the incoming parallel data to over sample. Note, over sampling the data, may result in added jitter to the output signal.

    You also mentioned that the TCLK and RCLK were tied together. Please provide the full schematic for your board so that we can better understand how the system is connected. A block diagram would also be helpful.

    Mike Wolfe

    DPS APPS / SVA

  • Hello

    I tried scaling down the input voltage of mux to less than 3.3 V , but still it doesn't get locked.

    USB signal doesn't get locked probably because of different data rates as USB 2.0 IS used so may be its not supporting as you too mentioned.
    And data rate of RS232 signal is in kbps so both signals doesn't get locked.
  • Hi,

    Can any one of you please suggest which serialiser and deserialiser could support the inputs and outputs respectively from USB, RS232, RS485 and Ethernet??

    Signals from these protocols are to be provided as input to serialiser and output from deserialiser.
  • Soniya,

     For any of the standards listed - USB, RS232, RS485, and Ethernet, there are multiple datarates and interface styles.  For example, Ethernet at the MAC level can be MII, GMII, RGMII, SGMII - all valid formats from 24 pins to a few as 4 pins.  USB could be 1.0, 2.0, or 3.0 with datarates moving to 10 Gbps for USB 3.1. 

    When describing the inputs to a serializer it helps to be very specific about datarate and the electrical characteristics of the signals.  RS232, RS485, USB, and Ethernet on a cable are all differential signals - this type of signal is not compatible with LVCMOS inputs.  USB signals are measured in mV, while RS485 signals are measured in V.

    In order for a serializer to properly transfer data from the parallel interface to the serial interface a couple rules must be followed.

    General Serializer Rules

    Data Inputs must maintain a constant phase relationship between the input Clock to the serializer.  This means that the data is synchronous with the serializer input Clock. 

    Serializer Clock and Data signals must meet all datasheet electrical specifications.

     The DS90C241 / DS90C124 serializer - deserializer pair can be used in many custom applications like you describe.  Generally not all at once since the different input datarates from USB - RSxxx - Ethernet are not typically synchronous with one another.  However, DS90C241 / DS90C124 features like auto DC balance for AC coupling support and Embedded clock-data recovery (CDR) make for a flexible interface which can be used to construct a data payload of several sub-types.

    With several standards to deal with simultaneously I suggest you look closely at the characteristics of each one to determine if they can be combined in a way which meets the datasheet requirements.  TI does not make a serializer - deserializer combination which directly addresses your need.  This type of custom combining and serializing function could be performed by a FPGA

    Regards,

    Lee

     

  • Hi,

    Thanks a lot for the information.