Modbus on Unitronics PLC

2rlp

Member
Join Date
Sep 2006
Location
Mumbai
Posts
136
Hi,

How does one connect a few Serial Devices and a GSM Modem on MODBUS of any UNITRONICS PLC.

Is the drawing attached the right method to do so?

Thanks

Ron
 
If these serial devices all have RS485 ports, then daisy-chain all the devices with 3-wire communication-grade cable.

There are RS485 t-taps out there that can convert a RJ45 or DB9 port to terminal blocks to make the wiring easier.

What are the make and model of the serial devices ?
 
Last edited:
The serial devices are microcontroller based custom designed. I havent used any GSM Modems before, but have a project lined up for the use of this combination.
 
You should use separate com port on Unitronics for GSM Modem.I think it will be used for remote programming or data collecting.
 
Hello 2rlp;

In that case you will need to provide a GSM modem with a Modbus RTU RS-485 connection. Do you have any special model in mind?
The closest item I know of to this are data loggers with GSM modem integrated. I think Sixnet I/O had a model of this kind; I'm sure other manufacturers exist, do a Google on it.
Hope this helps,
Daniel Chartier
 
Hello 2rlp,

What you want to do, the way you want to do is practically impossible! Modems, supported by Unitronics have RS232 port. More serious problem is, that modems have different (AT commands) protocol and it cannot run in the same network as Modbus. This is not Unitronics problem - it's general.
The simple solution is to use controller with two ports. Unitronics has Vision series controllers, which have more than one RS232/485 ports. You can use, for example V120, which has exactly the same dimensions and I/O configuration as M91 you're trying to use now, but is much more powerful. It has two fully programmable RS232/485 ports. With V120, there is no any problem to set one of the ports as RS485 Modbus Master and the second - to communicate with modem (PSTN/GSM/CDMA). In case of celular modem, you can exchange SMS. With GSM modem you can comunicate GPRS too.
You can take a look on Unitronics web site www.unitronics.com, to ask help from their support (free of charge, send mail to [email protected]) or post a question to Unitronics forum via their web site.
 

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