GE D20 Technical Overview page 63

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• Control Rules:
− If two requests are destined for the same digital output point, they will not be applied
concurrently; instead, they will be applied sequentially. (Control requests can be
conducted concurrently, but only if one of the requests requires a master relay.).
− If two requests requiring master relays are destined for different digital output points,
they can be conducted concurrently, as long as each request is associated with a different
set of master relays.
• Simultaneous Digital Output Points: D20/D200 peripherals support the simultaneous
control of digital output points, where these output points must be operated at precisely the
same time.
• Request Queuing: Control operations can be queued, where this is required by the
application.
• Request Repetition: Control pulse trains can be generated, where this is required by the
application.
2.4.8.4 D20K Base Application
The base application of the D20K controls five main functions:
• Control Block Processor makes the control blocks active, sets a timer if, required, and sets
bits in the relay driver to activate the relay on the next pass of the relay driver.
• Relay Driver is an interrupt-driven routine that runs every 500 µs to check the status of the
relay coils. The Local/Remote switch physically cuts driver power to control relays,
preventing operations in the local position. Once the switch is placed back in remote mode,
normal operations resume. The relay driver also writes to the two relay-state tables, and reads
back and verifies what has been written to the tables.
• Timer System is a linked-list timer that looks after the timing functions required by this
application (e.g. timing of arm messages).
• Communication Interface is a set of address tables and functions that implement
communication requests. Arm and Execute messages are used for all trip/close operations.
• Maintenance Interface consists of functions that provide background and on-line
application diagnostics, application initialization, and maintenance displays through the
maintenance port.
• Failure Detection detects loss of relay drive power, interposing power loss, and failure of an
output driver.
GE Information
D20/D200 Technical Overview
PRPI-019-3.00-10
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