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  1. #1
    Join Date
    Mar 2009
    Location
    Denton, TX
    Posts
    94

    Modbus over RS422 to JACE

    I have a device that is sending Modbus over RS422. I need to get that to my JACE6 which has a RS485 port. Can the RS422 four wire be connected to a two wire RS485 port? Most of the serial converters I have are going from RS232 to either 485 or 422.

  2. #2
    Join Date
    Aug 2009
    Posts
    2,459
    You can tie the wires together to convert from 422 to 485.

    If I remember correctly, you only have to tie the two positives together and the two negatives together.

    Anyone else agree?

  3. #3
    Join Date
    Feb 2005
    Location
    Edmonton, AB Canada
    Posts
    598
    Quote Originally Posted by BACnet View Post
    You can tie the wires together to convert from 422 to 485.

    If I remember correctly, you only have to tie the two positives together and the two negatives together.

    Anyone else agree?
    Good day Bacnet,

    Electrically each manufacturer has there own terminology and so this may or may not work... however, if it is wrong it will not damage anything. Eventually you can make this work electrically if you connect the right combination.

    As for it working at the protocol level... maybe... RS422 is a full duplex protocol whereas RS485 is half duplex... i.e. with RS422 you can transmit and receive at the same time. With RS485 you can only do one at a time and there are delays from switching from transmit to receive and vice versa. So depending if the Modbus server and/or client do not have sufficient delays between Transmit and Receive, your communication will be unreliable.

    It is certainly worth trying though.

    Cheers,

    Sam

  4. #4
    Join Date
    Mar 2009
    Location
    Denton, TX
    Posts
    94
    Thanks for the quick response. I will try it out and report back.

  5. #5
    Join Date
    Nov 2007
    Location
    Phoenix, AZ
    Posts
    256

    422 to 485

    Quote Originally Posted by jjackson7 View Post
    I have a device that is sending Modbus over RS422. I need to get that to my JACE6 which has a RS485 port. Can the RS422 four wire be connected to a two wire RS485 port? Most of the serial converters I have are going from RS232 to either 485 or 422.
    jjackson7
    You are going to have to get a RS422 to RS485 converter. The two serial ports are different. RS422 is an Industrial type and RS485 is what the rest of us use. You can't tie the wires together because of this. The responses are for full duplex RS485, 4 wire.
    Greg

  6. #6
    Join Date
    Feb 2005
    Posts
    1,219
    I am with GregF, may be try something like this:
    http://rs485.com/fullphotos/rsfc44tfull.html

  7. #7
    Join Date
    Mar 2009
    Location
    Denton, TX
    Posts
    94
    Yeah. I haven't had any luck yet. I will look into that converter.

  8. #8
    Join Date
    Jan 2008
    Location
    Taxachuesetts
    Posts
    198
    We have used the Telebyte Model 285 (RS-232 to RS485 4 wire) connected to Comm1 (RS-232 port on the Jace) and worked fine.

  9. #9
    Join Date
    Mar 2009
    Location
    Denton, TX
    Posts
    94
    Got the converter in. Trying to connect an AutoFlame DTI to a Jace 6 using Modbus RTU. Have to Modbus Async network up and can't get the DTI to talk. No comm lights coming on on either the DTI or the Jace. Anyone try to integrate one of these? Any help appreciated.

  10. #10
    Join Date
    Feb 2009
    Location
    Northeast
    Posts
    343
    Try http://bb-elec.com They will be able to tell you if the wires will work. They may be able to help with the protocols. I am just a customer who has used their products and advice from time to time.

  11. #11
    Join Date
    Jan 2008
    Location
    Taxachuesetts
    Posts
    198
    Quote Originally Posted by jjackson7 View Post
    Got the converter in. Trying to connect an AutoFlame DTI to a Jace 6 using Modbus RTU. Have to Modbus Async network up and can't get the DTI to talk. No comm lights coming on on either the DTI or the Jace. Anyone try to integrate one of these? Any help appreciated.
    I am assuming you have powered the RE Smith converter. What comm port is Modbus using 1 or 2? Have you added a modbus device to the network and tried pinging the device? (stay away from using address 1)

  12. #12
    Join Date
    Sep 2005
    Location
    Bay Area, Ca.
    Posts
    39
    Were you able to get the DTI to communicate with the Jace? I am currently working on one right now.

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