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Connect ME and RS-485 RS485

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For anyone who might be interested in connecting directly to RS-485 devices with a completely hardware solution, I have managed to make this work in a very clean, simple way. As discussed in other threads, the RTS pin is not easily utilized for flow control on the Connect ME. Others have tried, apparently with mixed results, to do a software work-around. This required no software changes. The same software that works on the development board works with this board.

If anyone is interested, reply to this topic, and I'll post a description of my solution.

Doug
asked Sep 23, 2009 in NET+OS by dbrouwer New to the Community (3 points)
recategorized Dec 18, 2013 by tuxembb

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3 Answers

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Doug - I am interested. Did you do something like tie the TX pin to something that drove the transmit line on the RS485 transceiver?
answered Sep 23, 2009 by charliek Veteran of the Digi Community (408 points)
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Hi Charlie--

I found a transceiver by Maxim that offers "AutoDirection Control". The transceiver is a MAX13487E. It's an 8 pin chip and pinout is quite standard. Pins 2 (Receiver enable) and pin 3 (shutdown) are both kept high at 5V+. Only pins 1 and 4 are connected to the Connect ME, pin 1 on the transceiver to pin 7 on the Connect ME, pin 4 to pin 8 on the Connect ME. While this sort of worked, I also needed to connect a 10K resistor between pin 1 and 5V+ to get reliable performance. Other than some filtering on the RS-485 output from the transceiver, this is the solution and it has worked well for me.

I hope this can help others who need RS-485 connectivity with the Connect ME.

Doug
answered Sep 23, 2009 by dbrouwer New to the Community (3 points)
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Hi,
I am trying to build connect digi connect me to RS485 port.

On one side I have TX,RX,CTS,RTS(coming out of an connect me chip) and on the other side I have the MAX485 chip.

Now, what Im trying to do is figure out how to switch the max485 from receive to transmit mode and vice versa.
I decided to use the RTS pin : so when asserted to 1 by connectme module I will also assert the max485 to tx mode and when RTS pin switches back to 0 I will put max485 in RX mode.
and I also connected the RTS to CTS on the connectme side.
Would that work?

Some people did this strategy but left CTS unconnected. but I don't know how this would work since connectme is asserting RTS to 1 and waiting for CTS to start transmitting so if you leave CTS not connected how would it work?


Now regarding your strategy wwould it be possible to send me some schematics? And some further explanation.

Sorry I am a newbie to electronic design and I would love to be able to build this thing

Thanks alot!


Kamel.
answered Mar 6, 2011 by Kamelzz New to the Community (2 points)
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