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ISO1452: RS422 transmitter part not working

Part Number: ISO1452

Hi 

I am using the above IC to convert UART data to RS 422 protocol, here i acn transmit data from uart to RS 422 but from RS422 i am unable to receive data,

  • Hi Sasi,

    Thanks for reaching out to us and for sharing the schematic with us as well.

    In the schematic, I am assuming that there are necessary termination resistors and protection circuits used on the RS-485 bus based on your EMC requirements. I also noticed that you have used 100Ω series resistor on both VCC1 and VCC2 supply path. 100Ω seems a bit high, when device consumes higher currents, especially on the VCC2, the voltage at VCC2 can go down significantly. This, under worst-cases, could make the device turn OFF momentarily. Even if it doesn't turn it OFF, the current limit could starve the device and not let it work normally. Hence, I recommend you to remove the 100Ω resistor and try testing again.

    If removal of 100Ω doesn't resolve the issue, then I would request you to test ISO1452 separately to isolate the issue. ISO1542 is only a physical layer device, it only converts the UART logic levels to RS-485/RS-422 compatible electrical signals and doesn't interfere with the actual protocol implemented. Hence, to check if there is any issue in the device, I would apply a 5V clock signal either A or B while keeping the other connected to GND2. The R output should match the signal on bus if clock is applied to A and should be inverted if the clock is applied to B.

    Please do the above experiment and confirm if the issue is in the device or in the RS-422 protocol implementation. Thanks.


    Regards,
    Koteshwar Rao