Modbus slave/master problems


Thread Starter


I need to run two separate Modbus networks on a TSX 3721 Micro PLC. I am planning to use the PCMCIA Modbus card to be a master to several downstream modbus devices. I am planning to use the built-in terminal port to connect to a building automation system as a slave device. My question is, would this work and could I use a Magelis or another brand of Operator interface somehow within these confines (could a magelis and a building automation system both be connected to the PLC as master, I don't know for sure).

Fernando Capelari - Schneider Electric B

Dear friend,

First of all: the Magelis HMI can not be a Modbus slave, only a master. So, if you want to use both ports of the TSX Micro as a Modbus master, you won't be able to connect a Magelis to the PLC.

What I suggest to you, is check if some of your slaves devices can connect on the Unitelway network. If so, you can add the Magelis as a Unitelway slave (instead of Modbus) on the same network. In this case you will have one Unitelway port and one Modbus port and the Magelis and all of your devices connected.

Remember that to use the built-in terminal port as a Modbus master the firmware of the PLC must be version 5.0 at least.
I'm not familiar with that PLC, but if it has two modbus ports, you should be okay. As a rule, any modbus network can have only one master, but many slaves. You could also install a Bridge MUX to allow several master devices to communicate with one slave.

Jerry Miille