12
Network Communications—N2 Communications Bus
General
•
Each NCM can support one or two N2 Bus. The devices that you place
on the N2 Bus must be daisy-chained devices, which include: NCM,
DCM, XBN, XRE, XRL, XRM, IAC, ILC, AHU, UNT, VAV, VMA,
LCP, IFC, D600, repeater, and surge protector. For more information
on using two N2 Buses, refer to
Dual N2 Bus Application Note
(LIT-6363145)
under
Application Notes: Network Communications
in
this manual.
Number of Devices
•
Currently, up to 100 devices can be connected to an NCM, including
repeaters. The actual number of devices is dependent on the features
and point count used in the NCM.
•
Special rules apply to the TC-9100 controller, where the maximum
number of devices can be from 60 to 200, dependent on the software
configuration in the NCM.
•
Up to 50 daisy-chained devices are allowed before a repeater is
needed. Add a repeater to the bus when you reach 49 devices. Count
each repeater as one device.
•
Any path from the NCM to an N2 device cannot go through more than
two repeaters or two pairs of fiber modems (i.e., cascaded
repeaters/modems). This is because the repeater/modem delays the
N2 Bus signal between Sides A and B. The N2 Bus can compensate
for only two of these delays; therefore, up to two repeaters or two pairs
of fiber modems can be cascaded in series. These configurations are
shown in Figures 12, 13, and 14. Note that the signal from the NCM
only passes through two repeaters or two pairs of modems to any N2
device.
•
For additional information on the maximum number of devices and
priority assignments, be sure to read
Guidelines for Efficient Operation
Technical Bulletin
(LIT-636341)
under the
Appendix
tab of this
manual.
Line Length and Type
•
A maximum of 1524 m (5000 ft) of daisy-chained cable is allowed
before a repeater is needed. Add a repeater to the bus when you reach
1524 m (5000 ft).
•
The maximum distance from an NCM to the farthest device, even
through repeaters, is 4572 m (15,000 ft).
•
You may use 18 through 26 AWG twisted pair wire; however,
Johnson Controls recommends 22 AWG or heavier, because lighter
wire breaks easily when stripped and installed.
