IBM SC33-1683-02 - Manual (Page 259)

TD_ADDR4
is the address of a value intended for CICS internal use only. It must not be
used.
TD_ADDR5
is the address of a value intended for CICS internal use only. It must not be
used.
TD_ADDR6
is the address of a value intended for CICS internal use only. It must not be
used.
TD_ADDR7
is the address of an area containing the value of SYSID.
TD_ADDR8
is the address of a value intended for CICS internal use only. It must not be
used.
Modifying fields in the command-level parameter structure
Some fields that are passed to transient data are used as input to the request,
some are used as output fields, and some are used for both input and output. The
method your user exit program uses to modify a field depends on the usage of the
field.
The following are always input fields:
QUEUE
FROM
SYSID
The following are always output fields:
INTO
SET
LENGTH is an input field on a WRITEQ request, and an output field on a READQ
request that specifies SET. It is both an input and an output field on a READQ
request that specifies INTO.
Modifying input fields
The correct method of modifying an input field is to create a new copy of it, and to
change the address in the command-level parameter list to point to your new data.
Note: You must never modify an input field by altering the data that is pointed to by
the command-level parameter list. To do so would corrupt storage belonging
to the application program and would cause a failure when the program
attempted to reuse the field.
Modifying output fields
The technique described in “Modifying input fields” is not suitable for modifying
output fields. (The results would be returned to the new area instead of the
application’s area, and would be invisible to the application.)
transient data EXEC interface program exits
Chapter 1. Global user exit programs 227