User manual

Computer Gateway User Manual 2-9 5/96
2.3.3
The CG assumes that it is communicating with a pre-R400 system until it receives a "CG
Database List" message (transaction code 47 or 147) from the host processor that requests
"CG Node List" information (list type 5). This causes the CG to do two things.
• The CG responds with information about the CG including the point-name length (8 or
16 characters) used on the local LCN.
• The CG changes the transaction codes used for the only "unsolicited" messages that it
sends to the host processor. Thus, any subsequent "Operator Message
Confirmation/Timeout" messages will use the transaction code of 101 and any "Turn on
ACP" messages will use the transaction code of 102.
For each host processor request where point name length is significant, response from the
CG will use the transaction code that matches with the request. For example, the response
to transaction code 5 is transaction code 8 while the response to transaction code 105 is
transaction code 108.
For those transactions where the response does not contain a point name, there is no long
point name transaction code. For example, both transaction codes 13 and 113 receive a
response of transaction code 14.
2.3.3 Internetwork Transfers
The host processor can request point data or file data from remote LCNs connected to the
local LCN through a Plant Information Network (PIN).
Point data transfers are directed to a specific LCN on the network by the inclusion of a two-
character "PIN node ID" field in the message. This field can be left blank when the point to
be accessed is on the local LCN. Long point name requests (see heading 2.3.2) can be
passed through a local LCN that is configured for short point names.
Some file transfer transactions also can be sent to remote LCNs (see heading 4.10.10.1 for
a list of remote file transactions). Addressing of a remote file requires the addition of a
three character prefix to the file name. This prefix is composed of the two-character PIN
node ID followed by a backslash (\) character (example: N1\NET>vdir>file_id.extension).
A file address without the PIN prefix specifies that the file is on the local LCN.
2.3.4 Restricted and Test Operation Modes
The ACP-to-ACIDP installation mode can be one of Normal, Not Installed, Restricted, or
Test. The Restricted and Test modes are intended to provide you with the capability to
inhibit ACP operation in ways that you may find useful in developing debugging aids for
the host processor. The only direct restriction placed by the CG on ACIDPs in either
Restricted or Test mode is to prevent cyclic or periodic scheduling (host processor,
operator demand and process specials only).
The CG treats ACIDPs in either Test or Restricted mode identically; however, you may
wish to enforce additional use restrictions at the host processor that differentiate between
those modes. For example, in Test mode you may wish to substitute test values for the
data specified by a get-data request.