PORTS Forum

Ports and Interfaces => Serial Ports => Topic started by: mdredmond on January 18, 2019, 05:22:11 pm

Title: What happens to lines when RS-485 driver is enabled?
Post by: mdredmond 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!

Title: Re: What happens to lines when RS-485 driver is enabled?
Post by: Jan Axelson 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.

Title: Re: What happens to lines when RS-485 driver is enabled?
Post by: mdredmond 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!

Title: Re: What happens to lines when RS-485 driver is enabled?
Post by: Jan Axelson on January 23, 2019, 09:07:25 am

Correct. You're welcome!