AN004. How to Send the Same Data to Several DS
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What's in this Application Note
We are often asked if it is possible to send the same data to several DS at the same time. We understand why such need may arise. For example, in RS485 systems there is often a master "node" that sends commands to several slaves. Every slave receives the command but only a particular one will reply back. This is because the frame (packet) sent by the master contains an address of the slave being addressed.
Network-enabling such system requires that this "send to all" communications method is somehow adopted to network communications. This Application Note explains how this can be done.
- Using UDP broadcasts to emulate multi-drop communications
Using UDP broadcasts to emulate multi-drop communications
The only way to arrange multi-drop communications system on the TCP/IP network is by using UDP/IP protocol and sending data as UDP broadcasts. TCP protocol is, by definition, a point-to-point protocol and cannot be used for data delivery to several nodes simultaneously. UDP, on the contrary, can and is often used to send the data to several nodes on the network.
To make one DS (we will call it "master") send data to several other DS ("slaves") through the network perform the following setup (only "important" setup changes are shown):
Same can be applied to using Virtual Serial Port as a "master". Use VSP Manager and set the properties of the VSP in a way similar to the setup of the master DS.
It is important to understand the limitations of such a system: