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SN65HVD1477: Pull up the Y output to 3.3V

Xiyao Zhao1
Prodigy 110 points
Part Number: SN65HVD1477

Hello,

we are using IC SN65HVD1477D for our BISS-C interface to communicate to an encoder.

We made a test to pull the Y pin ( which is used for the clock+) up to 3.3V for 1s, but our system could detect no data error and went on working.

I would like to ask, if  the Z pin could compensate voltage output if the Y pin was pulled up?

PS: We also made one test to pull the Y pin down to GND. This time we could trigger the system error as we expected.

Thanks in Advance.

Kind wishes!

Xiyao Zhao

                 

  • 0
    Guru 316640 points

    The Y and Z pins are inputs. They are used for the clock signal only at the slave device. But it sounds as if you are using the SN65HVD1477 at the master? Can you show a schematic of your circuit?

    What matters for RS-422 signals is the differential voltage, i.e., A−B or Y−Z. The most reliable way to prevent the differential signal from going through is shorting the termination resistor.

  • 0 in reply to Clemens Ladisch
    Prodigy 110 points

    Yes, shorting the terminal resistor is one of the tests. Shorting the terminal resistor could trigger the system error as we expected. The test I mentioned is to pull the Y pin up to 3.3v to check if the system error state will be triggered if the clocking line is pull up to the supply voltage. It seems like the Z pin could compensate the pulled up voltages applied on the Y pin. We used the Y and Z for the clock signal transfer from the microcontroller to the slave.

  • 0 in reply to Xiyao Zhao1
    TI__Guru 52102 points

    Hi Xiyao,

    How are you pulling up the device - are you forcing the pin to be high with  a direct connection - or is there is a resistor pulling up the line - if there is a resistor please could you indicate its values. Also is the system terminated? 

    Best,

    Parker Dodson