4
Network Communications—N2 Communications Bus
The N2 is based on Opto-22
Optomux
protocol, which was designed
for industrial applications, and is a proven communication network. The
N2 Bus follows the electrical characteristics of Electronics Industry
Alliance (EIA) Standard RS-485. It is optically isolated between itself and
other devices (except UNT100/101, VAV100/101, and Companion
Personal Computer), assuring reliable operation and noise immunity.
The NCM101/102 provides two bus channels: Channel A and Channel B.
Channel A is typically used for the N2 Bus. Channel B is used for the L2
Bus, including connection to C210 and C260 application specific
controllers.
For the NCM200, the N2 Bus interface is built-in and the L2 Bus interface
is provided by installing an L2 Bus submodule in the NCM’s
communications submodule slot.
The N2 Bus carries all communication between the NCM and the N2
devices. The types of data that go across the bus include:
•
commands from the NCM to an N2 device
•
data requests from the NCM to an N2 device
•
responses from an N2 device to the NCM, including identification,
changes-of-state, advisories, and requested data values
•
complete databases for N2 devices
•
time synchronization message from NCM
The N2 Bus connects an NCM to other N2 devices either internally or
externally. Internally, devices in the Network Control Unit (NCU) are
connected to the N2 Bus via the base frame on the NCU (Figure 2).
Connection occurs when you plug an N2 device into the NCU. No manual
wiring is required.
Externally, N2 devices are connected to the N2 Bus via the terminal block
on the device or the Communication Terminal Board (TBC) if the
connection is at an NCU or Network Expansion Unit (NEU). Connection
occurs when you terminate the N2 wires between the terminal blocks and
TBCs. Refer to Figure 2.