Specifications

field. MJD/MPM should reflect the “best available estimate” of station time as known to the sender.
A satisfactory “best available estimate” can be obtained simply by calling an appropriate time func-
tion immediately prior to assembling the message and sending it, and it is expected that this time
will represent the time at which the message was actually transmitted to within a few milliseconds.
See Section 6 for examples of command and response messages.
5 Message Types
Messages from MCS are commands. Commands can request action, information, or both. Connected
subsystems respond as specified by the message TYPE definition. The following is a list of message
TYPEs that are common to all MCS interfaces. ICDs between MCS and specific subsytems may
specify additional message TYPEs.
• “PNG” = Ping. The purposes of the command message are (1) to confirm that a commanded
system is functioning, and (2) to disseminate or confirm time information. Upon receiving this
message, the commanded subsytem (1) verifies that its local time is consistent with the time
given in the received command message, updating if neccessary; and (2) responds with a PNG
response message. The DATA field of the command message is empty, the DATA field of the
response message is limited to the standard response indicated below. See Section 6 for an
example.
• “RPT” = Report. The purpose of this message TYPE is to provide a flexible method for
reporting subsystem status. In the command message, the DATA field contains a label corre-
sponding to MIB entry or branch, indicating that the commanded subsystem should respond
with the current values of the MIB for that index/branch. The MIB data is provided as a
contiguous block of data, with no delimiters or terminators (this is to avoid difficulties with
raw data being interpreted as special characters). MIB entries that have variable length are
sent padded to their maximum length. MCS shall not send an RPT command that results in
a response message whose length exceeds the maximum specified by this ICD. See Section 6
for an example of the use of this command.
• “SHT” = Shutdown. The purpose of this command is to direct the system to shut down.
If the DATA field is empty, then the shutdown should be “orderly”; e.g., tasks which are
currently executing may be allowed to complete or be “gracefully” terminated. If the DATA
field contains the string “SCRAM”, then the subsystem should be shutdown as rapidly as
possible; e.g., tasks which are currently executing should simply be abandoned.
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If the DATA
field contains the string “RESTART”, then the subsystem should immediately restart after
shutdown is complete. The data field “SCRAM RESTART” is permitted and has the expected
effect.
The controlled subsystem shall respond to every message with a matching DESTINATION (or
“ALL”) with a “response message”. This is demonstrated by example in Section 6. The response
message shall be transmitted within 3 seconds of receipt of the ass ociated message from MCS. If
the DESTINATION field is not a match (or “ALL”), then the controlled subsystem shall ignore the
message. The DATA field of a response message has the following structure:
1. R-RESPONSE [1 byte, ASCII]. This is the character “A” to indicate that the command was
accepted, or the letter “R” to indicate that the command was rejected.
2. R-SUMMARY [7 bytes, ASCII]. This is MIB entry 1.1.
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The intent of the “SCRAM” option is provide a quicker method for shutting down the station to save time during
integration, commissioning, and maintenance activities, when many power-up/power-down cy cles may be required
and there is no risk of data loss. (It is anticipated that the option will exist to simply cut power to a subsystem, but
that that this will be facilitated specifically through station PCD.)
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