Multi-Drop Operation; Rs485 Multi-Drop Connections - Edwards nXR30i Instruction Manual

3.7

Multi-drop operation

Using multi-drop mode, a single computer system can communicate with more than one pump. Each pump must be
assigned its own individual address, or node, before it can be fitted into a multi-drop system. The command to assign
the multi-drop address is sent in standard message format and is detailed in
The message protocol in multi-drop mode is marginally different to that described for serial messages in single pump
systems (Section 3.4). The main differences in multi-drop message protocol are detailed below:
All multi-drop commands, queries or replies have the start character #.

All multi-drop commands, queries and replies include a header, which contains the address of the node that

the message is to, followed by the address of the node that the message is from.
There is a delimiter character ':' (colon) which separates the two multi-drop addresses in the header.

The remainder of the message (command, query or reply) follows the same protocol as already described for

single pump systems.
The wild card address 99 means 'any' node.

After a pump has been assigned a multi-drop address, it will ignore any messages in the format for single pumps. An
individual pump will remain silent and ignore all command messages unless the multi-drop address matches its own
address.
Figure 5 shows a schematic diagram of an example multi-drop connection system, which can be expanded to
accommodate multiple pumps.
1. RS485 interface on control equipment or PC
2. Pump logic interface
Figure 5 - RS485 multi-drop connections
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Section 3.7.1 below.