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Subject: RS485 Full duplex question

Date: 11/13/02 at 4:31 PM
Posted by: Darren
E-mail: dazlogan@aol.com
Message Posted:

Hi all,

I want to design a full-duplex multi-point RS485 system using for example the LTC490 (or MAX490) RS485 transceiver chips on each node.

However, I just cannot understand how you multi-drop these devices ??
The chips have no transmit enable/disable pin so you cannot put the outputs into a high impedance state, therefore, every device will have it's outputs connected to the bus at the same time - surely this will cause bus contention ?

(Before anyone says it, I know you can get devices with enable/disable pins on-chip but I really must know how these devices are supposed to be connected together first).

Thanks,
Darren


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