Building a multi-drop network, Guidelines, Examples – Honeywell CONTROLBUS QS7800B User Manual
Page 6: Network with maximum of 198 subnetworks, Network with maximum of 222 subnetworks
QS7800B NETWORK INTERFACE CONTROLBUS™ MODULE FOR MULTI-DROPPING 7800 SERIES RELAY MODULES
65-0227—2
6
BUILDING A MULTI-DROP NETWORK
Guidelines
The subnetwork addressing in the Q7700 Network Interface
Unit (NIU) is not contiguous. It is divided into two blocks,
containing 198 and 24 addresses, respectively. A maximum
multi-drop configuration would include 222 subnetworks (198
plus 24) on a single Q7700 NIU. Because the 24 subnetworks
are not contiguous, connect them to a separate Q7700 NIU
slot.
One QS7800B ControlBus™ Module card supports up to 31
multi-drop subnetworks without using an RS-485 repeater. If
an RS-485 repeater is used, up to 61 multi-drop subnetworks
can be supported by one QS7800B card. The RS-485
repeater must be installed between the 30th and 31st
subnetwork.
Each subnetwork includes one 7800 SERIES controller with
or without an S7800 Keyboard Display Module and/or an
S7830 Expanded Annunciator. An S7810B1007 Multi-Drop
Switch Module is required in each subnetwork. See Fig. 6 for
wiring information.
Subnetworks can be spread evenly (balanced) across the NIU
slots. This will help to speed communications.
It is recommended that the multi-drop network be built starting
with slot number 1 of the NIU, according to the guidelines
above.
Record the serial number and physical location of each
S7810B Multi-Drop Switch. This data will be useful when
commissioning the ZM7850 Combustion System Manager
(CSM) software. (Reference CSM manual, form 65-0102, for
CSM commissioning.)
Examples
Network with Maximum of 198 Subnetworks:
The open NIU slots can be used for other QS7800 ControlBus™ Module Cards.
Network with Maximum of 222 Subnetworks:
NOTE:
For networks that have more than 198 subnetworks,
the last NIU card slot must have the 199th through
222nd subnetwork attached to it.
The open NIU slot can be used for other QS7800 ControlBus™ Module Cards.
NIU Slot Numbers
1
2
3
4
5
6
Total
Number of Subnetworks
61
61
61
15
Open
Open
198
Subnetworks Balanced
33
33
33
33
33
33
198
NIU Slot Numbers
1
2
3
4
5
6
Total
Number of Subnetworks
61
61
61
15
24
Open
222
Subnetworks Balanced
40
40
40
39
39
24
222