Figure 1 shows the control
blocks that are accessed by both the terminal control layer and the
DFHIR layer. Figure 2 shows the
location of these control blocks in MVS virtual storage. Figure 1. Control blocks
accessed by CICS/MRO terminal-control layer of control blocks and
by interregion SVC layer of control blocks
The following blocks are used by both the terminal control layer
and the DFHIR layer. These blocks are allocated at logon time within
a single MVS GETMAIN, and, unless otherwise stated, reside in subpool
251 of MVS storage.
Subsystem logon control block (SLCB)
The SLCB is used by the IRC
SVC and region and contains the main ECB, posted when the region
has IRC activity. It is pointed to by the CRB and LCB.
Subsystem connection address control block (SCACB)
The SCACB contains entries allowing the addressing of SCCBs from
the SLCB.
Subsystem connection control block (SCCB)
The SCCB is created for each IRC send-receive session, and is
allocated at logon. It contains the ECB, posted when input for the
session is available.
Note: There is a one-to-one relationship between
TCTTEs and SCCBs when they are in use.
Figure 2. Location of control blocks in MVS virtual storage
