First, how many devices can we connect to our Modbus network?

Second, which type of Modicon processor is best suited to support 150 I/O andmore than 2 Modbus ports. The network is Modbus over daisy-chained RS485.

Let me know if you need more detail.

Thanks,
Henry

 

Daisy chained RS485 networks are usually limited to 32 devices maximum. The use of a repeater can extend many networks to 64 devices.

Modbus does not manage collisions so, only one Modbus Master device should be used (active) per network.

For more than two Modbus networks look at either the TSX-Premium or the TSX-Quantum families.

Why do you want/need more than 2 Modbus networks in your system?

 

> First, how many devices can we connect to our Modbus network?

Modbus allows a maximum of 247 addresses. Usually physical constraints will limit the practical number of nodes to a much lower value. E.g.-generally you can only have 32 devices on an RS485 segment, and at some point response time becomes an issue. I have found that anything over 5-10 nodes is iffy.

> Second, which type of Modicon processor is best suited to support150 I/O
> andmore than 2 Modbus ports. The network is Modbus over daisy-chained
> RS485.

Just about any of the Modicon processors will support 150 I/O, except for the micro units. As for more then 2 Modbus ports, you would need to look closely for this answer. I am not all that sure why you would need so many ports. Its possible to add port expanders or bridge muxes and get basically as many ports as you want, but again response time is an issue.

> Let me know if you need more detail.

YES! You have given out about 10% of the requirements, so its very difficult to give you any kind of serious answer.

> Thanks,
> Henry

Bob Peterson