Network Communications—N2 Communications Bus
5
INOUTCON
TBC
TBC
TBC
2-slot NEU
5-slot NCU
1-slot NEU
ASC
(ILC Shown)
DCM XM NCM XM DCM
DCM XM
DCM
N2 Bus
External Wiring
Internal Wiring
Base
Frame
Base
Frame
Base
Frame
N2 Bus
Figure 2: Internal and External N2 Bus Connections
The N2 Bus has three different types of communication, four priority
levels, and a specific method of data transmission.
The N2 Bus features three different types of communication, which may
come from either an NCM or any user interface device: offline poll,
online poll, and general communication. The NCM initiates all
three communication types.
•
Offline Poll
--a request from the NCM to re-establish communication
with an offline device. This type of poll occurs continually between the
NCM and each offline N2 device that is defined in the NCM database.
An offline device is polled once after every complete scan of all online
devices. Once communication is established, the NCM begins sending
online polls to the device.
•
Online Poll
--a request from the NCM to the N2 device for any status
changes. The NCM polls devices continually, according to the priority
levels assigned to the devices. Polling is interrupted momentarily when
a command is issued through general communication.
•
General Communication
--commands and requests that come from
application programs or operator devices. These can occur anywhere
on the network. This type of communication takes precedence over
polling. After general communication finishes, polling of online and
offline devices resumes.
Theory of
Operation
Communication
Types