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Apu3cX easiest way to get Full com port that is not com 1?

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    wriver4 - Posted Sep 5th

    I realize NCT5104D is configurable.

    The customer has seen the board and wants to use com1 to connect the 5v modbus "proprietary RS485" to it.

    I am having significant difficulties explaining to them why using com1 is a really bad idea.

    This is not a deliverable at this point in time but comming soon.

    I have other deliverables before this one.

    Can someone give me a how to about the easiest way of creating a full ( = com1 5v capable) comX port?

     

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    miczyg - Posted Sep 6th

    wriver4 - Posted 27 Hours Ago

    I realize NCT5104D is configurable.

    The customer has seen the board and wants to use com1 to connect the 5v modbus "proprietary RS485" to it.

    I am having significant difficulties explaining to them why using com1 is a really bad idea.

    This is not a deliverable at this point in time but comming soon.

    I have other deliverables before this one.

    Can someone give me a how to about the easiest way of creating a full ( = com1 5v capable) comX port?

     

     


     

     

    Hi wriver4,
    Using COM1 is strongly not advised, since firmware is printing messages to that port. It could be also used in the OS as a console. 

    From looking at apu3c schematics COM2 has no flow control pins exposed on J4 header.
    By looking at page 12 on apu3c4 schematics: https://www.pcengines.ch/schema/apu3c.pdf
    the only solution I can see is to use 4th uart on nct5104d, since 3rd uart is connected to PCIe expansion (see page 17).
    All necessary uart signals would be provided on J20 GPIO header pins 11-18, inputs are 5V-level TTL and outputs have 12mA source-sink capabiity.
    Additionally You have GND and 5V on pins 19-20. You can possibly enable this uart in firmware by enabling UARTD in sortbootorder (Payload [setup] option in SeaBIOS).

    I am not 100% sure however if flow control will work, IMO it should. Also I would have to check whether the outputs drive 5V level or 3.3V level as nct5104 power supply.

    Given that You would have full UART which You could then connect to a UART-RS485 converter or something like that.
    This is the easiest way I can now think of.

    Good luck.


    Post last edited Sep 6th
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    wriver4 - Posted Sep 7th

    @miczyg Thanks for your analysis. While I only had time to skim the documentation, I essentially came to the conclusions you have. I did not get to your level of detail (the skim factor) thanks for that. I really appreciate your time.

    To me this an important discussion for other members to see the versitility of these devices.

    There is another post from May 2015 about APU1D4 with a link to bios to have 4 comports 2 on the gpio for those who are interested.

    Suddenly, Com2 has become attractive to the customer.

    Thanks again!

    Cheers

    wriver4

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