Multi-Drop Mode - Edwards EXT75DX Instruction Manual

B722-40-880 Issue H
Figure 9 - Schematic diagram of the logic interface connections
1. RS232 interface on control equipment
2. 24 V d.c. electrical supply
3. Fuse
4. Optional LED indicator - system OK
5. Optional LED indicator - normal speed
6. Current limit resistor for LED
3.7.7

Multi-drop mode

Using multi-drop mode, a single computer system can communicate with more than one DX pump. Each DX pump
must be assigned its own individual address before it can be fitted into a multi-drop system. The command to assign
the multi-drop address is sent in standard DX message format (as detailed in
The message protocol in multi-drop mode is marginally different to that described for serial messages in single pump
systems. The main differences in multi-drop message protocol are detailed below:
All multi-drop commands, queries or replies have the first character #.

All commands, queries and replies contain a header containing 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 is very useful and means 'any' node.

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7. Optional serial mode selector
8. DX pump
9. Optional voltmeter
10. Optional serial enable switch
11. Optional standby switch
12. Start switch
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Section 4.1.10.