Enhanced Programmable Logic Controller Gateway
Enhanced Programmable Logic Controller Gateway
This article is describing about EPLCG (Enhanced Programmable Logic Controller Gateway). The EPLCG provides a link between the Local Control Network (LCN) and Programmable Logic Controllers that use Modbus Subsystem or Allen Bradley protocols. The EPLCG is one of the modules on the LCN. It communicates with other modules on the Local Control network and with programmable logic controllers which are connected to one of the EPLCG's two EIA RS-232 ports.
The EPLCG makes the transition from the transmission technique and protocol of the Local Control Network to the transmission techniques of the Modbus or Allen Bradley protocols in the TDC 3000X system architecture.
Two ports on the EPLCG can serve independent Programmable Logic Controller networks or can be configured optionally to provide redundant communication paths to a PLC network, including Allen Bradley's. The two ports are guaranteed to support up to 18 Programmable Controllers, up to 64 programmable controllers can be addressed. The EPLCG handles up to 3000 process points.
Programmable logic controller on either the Allen Bradley DF-1 protocol or AEG-Modicon Modbus RTU Protocol are accommodated by the EPLCG, for both protocols on one EPLCG, each is accommodated by the one of the two parts. The EPLCG accomplishes data form conversions necessary to provide data to the LCN (Local Control Network) and to transfer data from the LNC to the Programmable Logic Controllers.
The EPLCG can operate as a single node on the LCN or it can operate as a node pair, with two EPLCG, one operating and the other serving as redundant partner, with an exact, up to date copy of the database, ready to take over full operation, should the operating member of the pair fail or be taken out of service.
The EPLCG provides the data buffering, conversion, and sequencing necessary to provide an efficient interchange of information between the programmable controller and the Local Control Network, and to accomplish the following system level services:
Stores user defined configuration data, including programmable controllers and data point tag data.
Optimizes and organizes programmable controller scanning tasks on the basis ports and device addresses.
Initiates communication over the external networks connected to the two ports to the programmable controllers, as defined by the configuration data and re-initiates communication after an interruption in communication.
Maintains an image of programmable controllers and network status for presentation on a Universal Station's Hiway Status display.
Maintain an image of values for all defined data points.
Maintains port operational statistic for use by technicians, including errors and retry counts, view words, last error codes, port traffic, firmware free time counters and number of Allen Bradley reports by exception processed.
The EPLCG provides the following services for acquiring data processing:
Repetitively acquires all defined data of programmable controller as fast as possible in a free running mode. A report by exception mode is available for the Allen Bradley protocol only.
Monitor alarm conditions and generates alarms when dictated by the acquired data. Provides change of state alarms for value limit and digital data or deviation alarms for analog data.
Provides a contact cut out function that suppresses unnecessary alarms from a secondary point, when configured predefined conditions, such as out of service equipment, are detected by a primary point.
The types of data points listed below can be configured for an EPLCG. Configuration data and process data for each of these points resides in one of up to eight emulated DHPs (Data Hiway Ports) in the EPLCG.
DHPs can be thought of as subdivisions of the EPLCG. They are virtually identical to DHPs that operate as individual boxes on the Honeywell Data Hiways. Each DHP in an EPLCG provides 30 memory slots, so an EPLCG has 8x30=240 slots.
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