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SN75ALS176: NRZ Random Code Generator

Marvn Arcangel
Genius 11220 points
Part Number: SN75ALS176
Other Parts Discussed in Thread: THVD1552, SN75179B, SN74LV374A, SN74HCS86, SN74AHC86, SN74AHC374, SN74LV86A

Hi Experts,

The customer needs help in setting up an eye diagram on my oscilloscope to check my RS-485 communication.

On page 18 of the report, there is a circuit to generate an NRZ Random code generator. And the customer would like to understand how this is connected. Please see the question below:

"I understand that pin 3 from the 555 goes to the scope trigger. I am thinking it does not matter on what edge it is triggered. I do not understand the "output to cable", "input to cable" and "output to scope" connections. can you explain these? I am thinking the "output to the scope" would go to channel 1 of the scope and possibly the trigger would go to channel 2. Is that correct?"

Thanks for the help.

Regards,

Marvin Arcangel

  • 0
    Guru 292510 points

    Pin 3 of the 555 outputs a regular square wave; you can indeed trigger on any edge. You can also replace the 555 with another source (which would be necessary for more than 2 MHz).

    The top transceiver is used only as a transmitter; the bottom transceiver is used only as a receiver. You connect them to the ends of the cable. (If you have a full-duplex transceiver like the SN75179B or THVD1552, you need only a single chip.)

    RS-485 signals are differential. For the eye diagram, connect the "input to cable" signals to two oscilloscope channels and compute their difference.

    "Output to scope" allows you to monitor the received digital signal, if you really want to.

    Possible alternatives for the three logic chips are SN74HCS86/SN74AHC86/SN74LV86A and SN74AHC374/SN74LV374A.

  • 0
    TI__Mastermind 48057 points

    Hi Marvin,

    Clemens is correct in his analysis - if you have any other questions  please let me know and I will see what I can do!

    Best,

    Parker Dodson