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Connection for serial control and monitoring
A735-01-860 Issue A
3.7 Multi-drop operation
Using multi-drop mode, a single computer system can communicate with more than one nXDS pump. Each nXDS 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 nXDS message format and is detailed in Section 3.7.1 below.
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 nXDS pump has been assigned a multi-drop address, it will ignore any messages in the format for single pumps.
An individual nXDS 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.
Figure 5 - RS485 multi-drop connections
1. RS485 interface on control equipment or PC
2. nXDS pump logic interface
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