Thanks Erik for Diagram it made things easy to understand

Russel ,
Even I am using MODBUS in this project
Now the design requirements are
To develop rs- 485 HUB with 5 ports (As suggested) to distribute load
HUB will act as local master & will communicate with PC using MODBUS
While going thru MODBUS specs I could not understand whether
MODBUS allows such arrangements?
Even though it acts as an application layer it defines data link layer with requirement of only Tx,Rx & Gnd on RS-232 Ports on physical layer.
In this case how to tackle issues like keeping PC(Master) waiting while comm. on internal network is active,
How to send high priority interrupts from any device to pc

I am trying to use UART on chip to communicate in both directions (toward pc & towards 485 n/w) with use of some switching between lines to control direction of communication with use of handshaking on pc side
Is it worth way of doing things or some standard or simple way exists

Hope to get reply

Thanks,
Kaiwalya