RS485 RS422 communication

Discussion in 'General Electronics Chat' started by ak52, Aug 5, 2016.

  1. ak52

    Thread Starter Member

    Oct 15, 2014
    145
    4
    Hello Everyone,

    I have a usb to serial converter (RS422) ,and would like to interface it with a sensor which communicates over RS485,it is possible to do it with my serial converter?If so please tell me the connections required and how do i give them for a full duplex mode?

    The serial converter has an FT232 which is connected to a MAX488CSA.

    PLease help.
     
  2. Sensacell

    Well-Known Member

    Jun 19, 2012
    1,131
    267
    What brand/model of converter? ask them?
     
  3. ak52

    Thread Starter Member

    Oct 15, 2014
    145
    4
    converter was made by me ,basically it was for rs232 ,but we wanted RS422 communication cabability.I have never used RS422 before so i donot know how to connect it physically.
     
  4. ak52

    Thread Starter Member

    Oct 15, 2014
    145
    4
    Edit:Attached schematic of the converter
     
  5. Sensacell

    Well-Known Member

    Jun 19, 2012
    1,131
    267
    If your device cannot tri-state (disable to hi-Z) the TX output, then you cannot use it for 485.
     
  6. ak52

    Thread Starter Member

    Oct 15, 2014
    145
    4
    I did not understand that.could you explain it more clearly with physical connections..(Where do RX+,RX-,TX+,TX- go...etc?)
     
  7. Sensacell

    Well-Known Member

    Jun 19, 2012
    1,131
    267
    RS-485 uses 2 wires to communicate bidirectionally.

    You must be able to disable your transmitter to allow reception, your circuit cannot do that.
     
  8. ak52

    Thread Starter Member

    Oct 15, 2014
    145
    4
    I see,thanks for clearing that for me :)
    What do i need to modify to make it compatable with RS422?

    Also if my slave is also a RS422 device how will the connections be set up?
     
  9. MrChips

    Moderator

    Oct 2, 2009
    12,442
    3,361
    You can add a MAX485 or equivalent IC (e.g. SN75176) to your existing design to provide RS-485 signalling.

    If the USB-to-TTL converter supplies the RTS signal, you can use this to enable the RS-485 transmittter (and disable the receiver) via the /RE and DE control signals on the MAX485

    Otherwise, you can use the first transition of TXD to trigger a monostable multivibrator in order to control the /RE and DE control signals on the MAX485. Set the pulse duration of the monostable to be just longer than the duration of one character. This may or may not cause a "turn around" interference depending on your situation.
     
Loading...