Modbus Plus networks can be used to service multi-purpose control applications, or they can be organized for the most efficient servicing of distributed I/O devices. This section compares the two approaches.

In multi-purpose control applications, the network is designed to allow communication between in programmable controllers, operator interfaces, and other kinds of devices.

For efficient servicing of distributed I/O, the network is designed to allow communication between one programmable controller and a group of I/O modules.

In multi-purpose control applications, timing can vary according to the current processing requirements of each node's internal program.

In efficient distributed I/O servicing applications, the timing of message transactions must be predictable to allow deterministic timing of the I/O control process.

In general applications, up to five networks can be joined by Bridge Plus devices to extend the cable length to 2250 m (7500ft) and the node count to 320 nodes.

In distributed I/O applications, messages are transacted on the local network only. BridgePlus devices are not applicable to networks used for distributed I/O.

Multi-purpose networks are not recommended for servicing I/O control applications in which I/O timing must be deterministic.