need help for parallel connection of rs485

[dsanthosh67]

Hi all,

Actually i am working with ADM2587E rs485 communication its works fine with single master and slave,but i am not able to connect multiple slave with single master.kindly help me for the connection,when i workout with this a junk value will received at the time of transmit a data....

Regards,
Santhoshkumar

 

[FvM]

RS-485 communication depends on only one peer activating Tx enable (signal DE) at a time. How is this achieved in your slave design?

It may be necessary to have pull-up/pull-down resistors for a proper bus idle state ("mark") when it's not driven by any side.

 

[dsanthosh67]

Totally i worked with 3 boards connected parallel,By default Tx enable pin(DE) is High and the Rx enable pin(RE) is low in all the boards.Then what's the solution...

 

[FvM]

I guess from your description that you are using the full duplex configuration as described in figure 42 of the ADM2587E datasheet (otherwise a single slave would work neither with permanently enabled transceivers).

The solution is to enable only one slave transmitter at a time and leave it disabled by default. Some UARTs are providing a transmit enable signal in hardware automatically (may need to be inverted). Otherwise the transmitter can be controlled by software or a hardware timer.

 

[dsanthosh67]

ya you are right when i work with single master and slave it works fine,more then one slave only the problem arise, i am trying to solve the issue by your way, Thanks for reply..