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LTM2882 communication issue

VKumar592
on Nov 4, 2020

Hi,

I am using LTM2882-3 in my design and implemented half duplex serial communication.

I am facing issue in  RS422 communication.

I did loop back on uart signals of processor  isolating LTM2882 it  is happening.

But when i use LTM2882 in the path no communication is happening in RS232 signals.

I am making DIN pin Low for RX functionality and High for TX functionality.

As per datasheet DE and Dout are shorted for Half duplex communication.

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  • +1
    •  Analog Employees 
    on Nov 4, 2020 12:48 PM 3 months ago

    Hello, 

    To implement half duplex communication with the LTM2882, the RS-232 transmitter and receiver lines must be connected together on the PCB. Have you connected the LTM2882-3 T1OUT to R1IN and T2OUT to R2IN on the PCB?

    The LTM2882 is an isolated RS-232 module. It's not suitable for RS422 communication. If you require RS-422 communication network, the LTM2881 and LTM2885 are the equivalent isolated RS-422 / RS-485 modules, alternatively the ADM2567E or ADM2867E are isolated RS-485 transceivers which will be the same function of isolating.  

    Regards,

    Neil 

  • 0 on Nov 5, 2020 3:45 AM 3 months ago in reply to NQuinn

    Hi,

    Yes, I have connected T1out to R1in since i am using only one channel i have not connected T2out to r2in.

    my communication network is rs232 only.

  • 0
    •  Analog Employees 
    on Nov 5, 2020 10:01 AM 3 months ago in reply to VKumar592

    It sounds like you have set this up correctly. Please ensure the ON pin is high. 

    What the the power supply of the VL, VCC and processor which has the UART? The processor voltage must be powered with the same supply as the VL supply, otherwise the T1IN input will not switch correctly. 

    Have you been able to confirm with an oscilloscope, that the T1IN pin is switching as expected, and whether the T1OUT signal is switching or not? 

    Regards,

    Neil 

  • 0 on Nov 6, 2020 6:13 AM 3 months ago in reply to NQuinn

    Hi,

    Power supply for VL,VCC and Processor is 3.3V and it is stable.

    Processor is also powered with the same voltage as that of VL supply.

    I am not able to capture it on CRO, but i ensured processor end by isolating LTM2882 and shorting RX and TX of Processor and i am able to see loop back happening.

  • 0
    •  Analog Employees 
    on Nov 6, 2020 8:57 PM 3 months ago in reply to VKumar592

    Ok so looks like the UART is working correctly. When you remove the short between Rx and Tx, what is the voltage on the Rx pin? Without an oscilloscope, you could view this signal with a DMM, and check whether ROUT1 is 0V, 3.3V, or high impedance.

    This will give information about what the receiver of the LTM2882 is doing. For example, if the ROUT1 pin is high impedance, this would indicate the isolated communication is not working correctly. 

    It's also worth checking the VCC2 power supply on the isolated side of the device, and ensure this is a stable 5V.

    Regards,

    Neil  

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  • 0
    •  Analog Employees 
    on Nov 6, 2020 8:57 PM 3 months ago in reply to VKumar592

    Ok so looks like the UART is working correctly. When you remove the short between Rx and Tx, what is the voltage on the Rx pin? Without an oscilloscope, you could view this signal with a DMM, and check whether ROUT1 is 0V, 3.3V, or high impedance.

    This will give information about what the receiver of the LTM2882 is doing. For example, if the ROUT1 pin is high impedance, this would indicate the isolated communication is not working correctly. 

    It's also worth checking the VCC2 power supply on the isolated side of the device, and ensure this is a stable 5V.

    Regards,

    Neil  

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