
BASIC VIU OPERATION
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3-7
SIG-00-07-11 SEPTEMBER 2012 (REVISED OCTOBER 2019)
Version No.: B.2
On startup, the VIU validates its configuration by verifying the following:
The MCF is valid.
The MCF CRC matches the MCF.
The correct UCN is entered.
If the MCF is valid, has the correct CRC, the vital configuration parameters are set and the
correct UCN is entered, then the VIU goes into the Fully Operational state. If any of these
checks fail, the VIU goes into the Un-Configured state. This will be indicated by a vital status
message scrolling on the bottom row of the front panel display.
NOTE
The status message is refreshed with each complete cycle of the
displayed information and may take approximately 2 minutes to cycle
completely and update the message. If the status
“UNCONFIGURED” and “SLV HEALTH BAD” displays, this may
appear for a few cycles until the message updates.
When the VIU is in the Un-Configured state, it does not send out any VIU vital messages or
respond to any VIU vital messages. It does, however, respond to input via the front panel
keypad and to messages from the Diagnostic Terminal (DT) program.
3.6
INTEROPERABLE TRAIN CONTROL MESSAGING (ITCM) SYSTEM
When the VIU is used in a Wayside Interface Unit Application, it will monitor signal aspects and
switch positions controlled by an existing interlocking, and/or defect detector status and send
the signal aspect and switch status, and/or detector status information to the locomotive and/or
the back office using Wayside Status Messages (WSMs). These WSMs and EMP messages
are transferred into the ITCM system using the Class D protocol. The ITCM will deliver the
WSMs to the locomotive or back office.
WARNING
THE APPLICATION LOGIC
MUST INCORPORATE
STABILIZATION LOGIC TO PREVENT UNSTABLE DATA BEING
SENT FROM MONITORED SYSTEMS.
3.7
GPS TIME REFERENCE
When equipped with a GPS receiver, the VIU synchronizes its time with the GPS receiver via
the GPS Interface. This can be either the internal GPS receiver or an external GPS receiver
connected to the serial port on the VIU top panel. Alternately, the time reference can be from
Class C EMP messages or via SNTP. In the absence of GPS time information the VIU is
capable of maintaining its internal clock time so that the drift from GPS time does not /-
2000 ms within a 24 hour period.