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TLK2501: Synchronisation issue

Kaustubh Kulkarni
Intellectual 1040 points
Part Number: TLK2501
Other Parts Discussed in Thread: TLK1501

Hello all,

A professor ask:

" We are designing a unidirectional optical data interface with a sending and receiving unit. To keep circuit simple, we are not using any micro-controller on both the units and thus the configuration of the TLK2501 is done by either pulling the pins permanently to VCC or GND, i.e. for e.g. TX_EN to VCC and TX_ER to GND for “Normal Operation”. According to the datasheet Figure 6 “Initialization and Synchronization State Diagram” to get into the “Normal Operation”-state after Power up, it is mentioned that after the power up either three “IDLEs” or “1 Valid Data” has to be send. To send an IDLE, the TX_EN would have to be changed to Zero, which in our case is not possible, since we connected TX_EN to VCC and TX_ER to GND. But the datasheet also say that “1 Valid Data” is also okay.

Thus my questions:

Is it okay, if we connect TX_EN to VCC and TX_ER to GND? How does the receiver synchronize to the received signal, i.e. recognizes the boundary between two consecutive words? Since we only have a unidirectional data transfer, the receiver can anyway not indicate to the sender, that there is a receiving error. Therefore I assume that it can automatically re-synchronize and no IDLE words are needed? "

Could anyone help me with this questions please?

Thank you in advance.

Kaustubh

  • 0
    TI__Genius 16150 points
    Hi Kaustubh,

    Basically the TLK2501 wait to receive 3 consecutive valid IDLES or Carrier Extends or 1 valid Data/Error propagation. Once either condition happens the device enters in SYNC state (Normal Operation).
    For transmission path (parallel to serial) data is valid on the rising edge of the GTX_CLK when the TX_EN = 'HIGH' & TX_ER = 'LOW', hence the enable, clock signals must be properly aligned (please take a look into figure 2 of datasheet).
    As you mentioned, the device to synchronize needs 3IDLE or Valid Data, in your case only valid data.

    I hope this helps.

    Best Regards,
    Luis Omar Moran
    High Speed Interface
    SWAT Team
  • 0 in reply to Luis Omar Moran
    TI__Intellectual 1040 points
    Hello Luis,

    Thank you for your answer.

    Could you please tell me how does the receiver synchronize to the received signal, i.e. recognizes the boundary between two consecutive words?
    Also as they are using only an unidirectional data transfer, the receiver can not indicate to the transmitter about a receiving error thus in this case, would it automatically re-synchronize or IDLE words are needed?

    thank you in advance.
    Kaustubh
  • 0 in reply to Kaustubh Kulkarni
    TI__Genius 16150 points
    Hi Kaustubh,

    According to the state machine of the device and the receive timing diagram, to sync the data, the device needs to receive 3 IDLE (K28.5) or 1 IDLE & Valid Data/Error, hence, the device won't re-synchronize automatically.
    The TLK1501 is not able to indicate to the transmitter about receiving error in a unidirectional data system, the user is able to monitor thr receive status signals thru RX_DV/LOS & RX_ER.

    Best Regards,
    Luis