Ports and Interfaces > Serial Ports

What happens to lines when RS-485 driver is enabled?

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mdredmond:
Hi,

I'm waiting for my copy of Serial Port Complete so forgive me if this question is answered there...

When a half-duplex RS-485 transceiver (like a MAX3471) has its driver enabled, what does it do to the bus to assert control and let other devices know it's getting ready to transmit? 

Thanks!

Jan Axelson:
Every half-duples RS-485 network has to have a protocol to ensure that only one driver is enabled at a time. RS-485 doesn't define the protocol. Options include:

A master node initiates all communications and in each message, specifies the node that should respond.

The nodes take turns in a specified order.

mdredmond:
Great, thanks!  The protocol is request/response.  I guess I just need to shut down the driver and enable the receiver as soon as the request is done transmitting. 

I appreciate your help!

Jan Axelson:
Correct. You're welcome!

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