User manual

Computer Gateway User Manual 2-6 5/96
2.3
2.3 SPECIAL SITUATIONS
The following paragraphs contain some additional material about CG characteristics that
may be useful, depending upon the specific way in which you wish to implement your
host-processor software.
2.3.1 Host Processor Scheduling of ACPs
The CG is designed to have the primary responsibility for scheduling of ACPs in the host
processor. The host processor itself can schedule operation of its ACPs, but restrictions
exist.
Full access to all CG functions requires an ACP to be connected to an ACIDP in the CG.
If the ACP is not attached to an ACIDP, it cannot store data to CRDPs or to other LCN-
resident data points, and it cannot receive messages from devices on the LCN or send
messages to Universal Stations.
See Table 2-1 for a summary of scheduling restrictions based upon ACP-to-ACIDP
connection and ACIDP installation mode.
Connection of an ACP to an ACIDP implies CG scheduling of the ACP, because there is
no "null" scheduling option. One method around this is to establish the ACIDP as demand-
only and establish logic at the host to ignore any unwanted CG activation.
For some of the transactions (messages) initiated by the host processor that normally
require use of an ACIDP name, the CG accepts a "blank" name (all ASCII spaces). See
Table 2-2 for a summary of these transactions.
Table 2-1 — ACP Scheduling Capabilities
ACP Is Connected;
Installation Mode is
ACP Not
connected
to an ACIDP
NORMAL RESTRICTED TEST
ACP can be initiated by
CG—Cyclic no yes no no
CG—Periodic no yes no no
Operator Demand no yes yes yes
Process Special no yes yes yes
Message Waiting at CG no yes yes yes
Host Processor yes yes yes yes