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Old May 23rd, 2017, 06:16 PM   #5
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Pete.S. is offline
Join Date: Mar 2016
Location: Fl
Posts: 464
If you want to use RS232 just put in a RS232 to RS422 (not RS485) converter on each side.
RS422 is duplex communication and doesn't require fail-safe bias resistors as RS485 do. Basically RS422 is the long range industrial replacement of RS232.

Otherwise modbus tcp is basically modbus embedded in a tcp package. You have an ip adress that has to be right. Other than that it is 99% the same.

The difference is that the checksum has been removed (because tcp communication have it's own checksum).

Also what is called slave address on serial is called unit id on modbus tcp. It should not be used by either the server or the client according to the standard but a lot of manufacturers screw that up. So it unit id/slave address has to be right as well.

"Server" on modbus tcp is the same as slave on serial modbus.
"Client" on modbus tcp is the same as master on serial modbus.
That can be a cause of confusion as well.

Last edited by Pete.S.; May 23rd, 2017 at 06:19 PM.
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