RS232 to RS485

Discussion in 'Computing and Networks' started by meera, Jul 15, 2008.

  1. meera

    Thread Starter New Member

    Jun 7, 2007
    6
    0
    i m using RS232 to communicate with my instrument, now i would like to change the RS232 point to RS485...

    i confuse with the point that i should use in RS485...

    the point that i use in RS232 are TxD,RxD,RTS,CTS

    but inside RS485 got TxD+,TxD-,RxD+,RxD-,RTS+,RTS-,CTS+,CTS-

    which point should i use in RS485...

    Thanks
     
  2. theamber

    Active Member

    Jun 13, 2008
    318
    0
    You probably have a 4 wire RS485 full duplex. Data is transmitted differentially in both standards. I suggest you buy a converter or build one with a MAX202 IC.
    Theoretically if the distance is short you may connect them straight it depends on the UART the devices have probably are 16C550 for older devices and 16C552 for new ones.
    However the range of the RS485 standard has a common mode voltage Vcm that the driver and receiver can tolerate of +12 to -7 volts so +13 and -8 may not be understood.
    This may help you understand:
    http://www.bb-elec.com/tech_articles/rs422_485_app_note/overview.asp
    This if you want to buy one converter:
    http://www.axiomatic.com/rs232-485-isolation.html
    I also recommend you this book:
    Programming and Circuits for Rs-232 and Rs-485 Links and Networks
     
  3. meera

    Thread Starter New Member

    Jun 7, 2007
    6
    0
    thanks a lot to your explanation...

    i get wat u mean..

    intinially i jus thought i only need to connect the wire Rx to Tx,that's all..

    i misunderstand that there are differentially in both standards...

    thanks..
     
Loading...