User manual

Computer Gateway User Manual 4-6 5/96
4.1.2
Header word 6 Host Task Identifier (2 ASCII characters)—This field has fixed values for
three CG-initiated messages and one host-initiated message.
– Turn on ACP (Transaction Code 2/102)—"DI"
– Time Synch (Transaction Code 31)—"UN"
– CG Restore (Transaction Code 43)—"RS"
– Restore Complete (Transaction Code 44)—"RS"
For all other message types, the codes are defined by the host processor
and are echoed in the CG responses. The Host Task Identifier is intended
as a message-routing code to be used by the host processor.
Header word 7 Message Tag (integer)—For internal CG use only.
Header word 8 Message Counter (integer)—For a dual-Bisynch link, this is a counter
(1..30000) sequentially assigned to each Data message (not to
Confirmation or Time Synchronization messages). The "send" and
"receive" counts are separate. After message 30000, the counter resets to
one. For a single link this value is not checked by the CG.
Note that header word 8 has a different meaning in negative Confirmation
Messages. See Paragraph 4.2.2 for details.
4.1.2.2 Message Data Formats
The format and content of data in each message is covered in the discussion of the
individual messages beginning at paragraph 4.2
4.1.2.3 Error Fields in CG Return Messages
Most Applications-Level data link messages are paired into requests and returns (see Table
4-3). Return messages from the CG can contain two types of error information:
• The Return Status word (found in all returns) shows whether or not the request was
successfully processed, and if not, what type of error was involved.
• Value Status words (found in data get or store returns) show if there have been any data
access errors that would invalidate the requested operation for a specified point-
parameter. There are over 200 different data access error codes that can be returned
(see the Messages Directory for a complete list of Data Access Status Codes).