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RS-485 Bidirectional Fan-Out Hub With Automatic Direction Control Reference Design

Roberto Panico
Prodigy 30 points
Other Parts Discussed in Thread: SN74LV08A

Hello,

this is my very first question.

Referring to the RS-485 Bidirectional Fan-Out Hub With Automatic Direction Control Reference Design, I would like to know why the R outputs of the 4 RS-485 transceivers are connected to the T input od the single RS-485 transceiver through the SN74LV08A and not directly. I mean, why the 4 R outputs are not connected together and directly connected ti the T input of the left transceiver?

I need to make an RS-485 bidirectional splitter (1 to N) with automatic direction control.

Thank you very much for the support.

Roberto

  • 0
    TI__Expert 6955 points
    Roberto,

    The SN74LV08A AND gate serves the purpose of combining the data from the four slave receiver outputs
    into a single driver input for the master. If more than one slave is communicating at a time, the data to the
    master will be corrupted due to collisions.

    -Lucas
  • 0 in reply to Lucas Schulte9
    Prodigy 30 points
    Hello Lucas,

    thank you for the support.

    So I cannot avoid using the AND gate to combine the data from the slave into a single input? Is there any possible alternative to pursue the same goal?

    I ask you this because I lack knowledge about this specific topic.

    Again, thank you for the support.

    Roberto
  • 0 in reply to Roberto Panico
    TI__Expert 6955 points

    Roberto,

    An alternate method for this is time division multiple access (TDMA), which allocates different time slots on a bus for each node to transmit its data. Another method is a master-slave protocol in which slave nodes would only transmit data when it is requested by a master node. A third method would involve token passing, which means that permission to transmit is granted through a token to one node at a time, and each node sends the token to the next node in a ring after it completes transmission. Also, you could use a shift register to toggle the enables of all the transverses and allow only one transceiver to send or receive at a time. 

    -Lucas