Modbus Master-Slave

Hi all,

I am using ML 1200 (1762L24BXBR) to communicate with Industrial PC Serially with Modbus using 1762-cbl-pm02. Here, Industrial PC is acting as Modbus RTU master and PLC acting as Modbus RTU master. Now i want to add another Industrial PC in current system which will be acts as Another modbus Master device.
Since their is only ONE communication port available on ML1200 so what changes do i need to make in my current system..? Can i use Port splitter ?

Note: Prog/HMI has been utilized by ENI utility module which is then directly connected to Industrial PC.

Modbus can only support 1 master on the network at a time. The issue with a port splitter is that both master A and master B may try to send a message to the slave at the same time. Or worse, master B may send a message while the slave is responding to master A.
ProSoft makes a module that allows you to connect up to 3 Modbus master devices to a single Modbus slave device:
http://www.prosoft-technology.com/Products/Gateways/Modbus-Master-Slave/Modbus-Serial-Port-Expander

The module listens on each of the 3 ports and when a Message matches the node ID in the configuration file it forwards it to the slave device. If while sending this message to the slave device another message comes in, it is placed in the buffer, and stored till communications with the other master device has been completed.

This would allow you to have 2 masters talking to the same slave.