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ISO1452: ISO1452 : RE/DE PIN CONFIGURATION

ALI KAYA
Prodigy 130 points
Part Number: ISO1452

Tool/software:

Hello for all,

I will use this IC in my RS485 application with full duplex mode, I confused about RE and DE pins configurations. If I shorted them is there any problem for full duplex mode?

As I know, RE has NOR gate ownself and DE is OR gate, therefore I want to use them together with just one GPIO pin.

Regards

  • 0
    TI__Mastermind 29375 points

    Hello Ali,

    It is common in RS485 applications to tie RE and DE together. However, for this will create a half-duplex behavior since the two pins will be in opposite states. If RE and DE are tied together, a '0' will enable the receiver (R) and disable the driver (D). A '1' on these pins will have the opposite effect.

    As you can see if RE and DE are tied together the operation will be half-duplex (the device cannot transmit and receive at the same time).  Full duplex will require separate control of the RE and DE pins.

    (+) [FAQ] ISO1452: [FAQ] How to configure a RS485 Full-duplex transceiver as Half-duplex? will have some additional information.

    Best,
    Andrew

  • 0 in reply to Andrew J
    Prodigy 130 points

    Hello Andrew,

    Thanks a lot, so  I have to connect RE and DE seperately for  full duplex. 

    What about RS422 full duplex application, same IC same thing?

    Regards

  • 0 in reply to ALI KAYA
    Guru 317260 points

    RS-422 and RS-485 have somewhat different electrical characteristics, but RS-485 is compatible with RS-422, so nowadays all transceivers are built with RS-485 characteristics.

    In practice, "RS-485" often means "half duplex" (one shared, bidirectional line) and "RS-422" means "full duplex" (unidirectional lines). So what you have asked about originally could also be called "RS-422".