User manual

Computer Gateway User Manual 4-12 5/96
4.2
4.2 COMMUNICATIONS HANDLER MESSAGES
The messages in this group are designed for use at the communication-handler level and are
not intended to be visible at the applications level.
4.2.1 Time Synchronization Message
This unsolicited message from the CG sends current time and date to the host processor
and is used by the CG during periods of host-processor inactivity to confirm that the data
link and host processor are ready to restart or continue to function properly. This is the
first message sent by the CG to begin the link-restart process.
Header information: Word 1—Transaction Code = 31
Word 2—Number of Words = 11
Word 5—CG Identifier = 1
Word 6—Host Task Identifier = UN
Message format: Words 1..11—22-character ASCII string containing date and time
in format MM/DD/YYbHH:MM:SS:NNNN (NNNN is a
millisecond counter).
Use information: The Time Synchronization Message does not require a Message
Confirmation. Instead, it requires an echo back of this message
by the host.
The host processor must echo back a Time Synchronization
message before the CG can send a Restart message. During
restart or during normal operation, the host processor must echo a
Time Synchronization message (or initiate any Data Message or
Confirm receipt of a message) within 1000 seconds to maintain
communication.
Time Synchronization messages are sent at 5-second intervals until
restart has begun, then at 15-second intervals at a priority lower
than that of any data messages.