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Hi, I'm running an Arduino-based home automation system. My custom-made Arduino clones are communicating over a RS485 network (configured as 8N1) using Modbus RTU protocol. Thing is that I want to have a reliable,  industrial-grade PLC in the network, in order to monitor my Arduino-based sub modules. Basically I need a cost efficient Unitronics PLC capable of connecting to RS485 network, The ladder program is expected to be non memory hungry, also I'm fine with good old 2 line display. The PLC must be able to connect to the RS485 network without the use of any extension modules/communication modules /.etc (native COM port on a screw terminal). 

Any suggestions?

Thank You.

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The Samba 35 with a RS485 add-on should do the job inexpensively. The Vision 120 or 130 would also do the job for a few dollars less, but the Samba has a MUCH nicer display.

The M91 would probably be the least expensive solution from Unitronics, with a 2-line display  and built-in 485 port, but uses the U90 Ladder software for programming which can be a bit more cumbersome than the outstanding VisiLogic programming software used for the Vision and Samba lines.

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I'm not a distributor so I don't have any price information, but I think there's only one serial port add-on for the Vision and Samba lines, although there may be an isolated port variant as well.

As far as the M91 and the V120/V130, I believe the serial port is built in.

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The cheapest way to go is an M91-2-R1 - $230 US.   RS485 is built into the COM port.

You could also go with a Jazz JZ20-R10 ($140 US) with a JZ-RS4 RS232/485 com port ($99 US).

If you don't need any I/O it will be much easier to use a V130-B1 ($269 US) which will allow you to use VisiLogic.  U90 software is rather cumbersome when it comes to communications.

Joe T.

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