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Author Topic: What happens to lines when RS-485 driver is enabled?  (Read 17634 times)

mdredmond

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What happens to lines when RS-485 driver is enabled?
« on: January 18, 2019, 05:22:11 pm »
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!
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Jan Axelson

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Re: What happens to lines when RS-485 driver is enabled?
« Reply #1 on: January 19, 2019, 11:09:01 am »
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.
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mdredmond

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Re: What happens to lines when RS-485 driver is enabled?
« Reply #2 on: January 22, 2019, 04:10:14 pm »
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!
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Jan Axelson

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Re: What happens to lines when RS-485 driver is enabled?
« Reply #3 on: January 23, 2019, 09:07:25 am »
Correct. You're welcome!
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