6 Control Modules—Network Control Module 200 Series
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In Network Port applications, the microprocessor:
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translates the host-generated requests to Metasys commands
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applies the various supervisory programs to the combined data,
supporting those functions that relate to the mapping of data
objects to the host computer (mapped analog data and binary data
objects)
All the software applications and supervisory routines take place inside the
NCM; data base exceptions and historical files are uploaded to the
Operator Workstation (OWS) (Item 3 in Figure 1) for reporting and
archival purposes.
The I/O subsystem supports a multi-user environment consisting of
integrated network connections (N1 and N2), submodule ports, and direct
I/O communication (NT [or Operator Terminal], RS-232).
N1 Local Area Network
N1 LAN communication is provided by the built-in N1 interface (Item 4
in Figure 1) terminating at a BNC connector at the bottom of the NCM200
module.
The N1 LAN is composed of the standard ARCNET
chip set and
hardware, allowing communication with both OWSs and other NCMs.
Each NCM and OWS on the system contains a “node manager” task,
whose responsibilities include:
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broadcast once per minute that it is still online
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listen to other node managers to track on and offline trunks
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issue a time stamp for every global data base in its memory
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compare the time stamps of its own data bases to the received time
stamps of other node managers’ data bases, and update the current
data base if necessary
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monitor the printer for online or offline status
The node with the lowest address number on the system issues time and
date information once per day to ensure system synchronization. Time
and date information is backed up by a clock/calendar chip (Item 5 in
Figure 1). The node manager also monitors broadcasts and issues
online/offline advisories.
In the event of a severed N1 network, each separated LAN forms an
independent network.
Communications
