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Vital Subsystem4.3. VRD (VITAL RELAY DRIVER) BOARD 59473-740-XXThis board plays a key role in assuring the vitality of the system. It produces an outputvoltage that operates a 100-ohm ALSTOM Type B1 relay (P/N 56001-787-05) if, andonly if, the data sent to it by the main processing system is exactly correct. If any ofthese checkwords are not precisely correct, the VRD output is shut off and the externalrelay de-energizes. The field energy that is delivered to the Vital output boards is brokenthrough front contacts of this Vital relay or a repeater of it. Thus, power will be removedfrom the outputs when the Vital checkwords are incorrect.4.3.1. Physical CharacteristicsThe processing portion of the VRD board is based on an 8085 microprocessor chip with4K of EPROM program memory and 4K of RAM. The RAM is shared with the mainprocessing system and is the means by which the checkwords are transferred.Figure 4-3. VRD BoardP2511G, Rev. Jan/06 4–4 ALSTOM Signaling Inc.
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