Viconics VTR7300 BACnet Integration Manual - Manual (Page 25)

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Maximum Number of Devices
A maximum of 64 nodes is allowed on a single daisy chain segment. A node is defined as any device
(Panel, Zone, Repeater, etc) connected to the RS485 network. Terminators do not count as a node.
To determine the number of nodes on a network, add the following:
 One node for each device, including main panels
 One node for each repeater on the chain
For the example in Figure 4, we have one node for the main Panel, plus 4 for the controllers, for a total of
5 nodes.
Figure 4: Five nodes network example.
If you have more than 64 devices, then repeaters are required to extend the network.
Maximum Cable Length
The maximum length of a chain is related to its transmission speed. The longer the chain, the slower
the speed. Using proper cable, the maximum length of an EIA-485 daisy chain is 4000-ft (1200 m).
This will only work reliably for data rates up to 100,000 bps. Viconics’ maximum data rate is 76,800
bps.
If you require a maximum network length of more than 4000 feet, then repeaters are required to
extend the network.
EIA-485 Repeaters
If you have more than 64 devices, or require a maximum network length of more than 4000 feet, then
repeaters are required to extend the network. The best configuration is to daisy chain the repeaters to
the main panel. From each of these repeaters, a separate daisy chain will branch off. Figure 5
demonstrates a valid use of repeaters in an EIA-485 network.