mation outside the PSW. There may be up
tosixteen 32-bit control registers. One or more specific bit positions in
control registers are assigned toeach facility requiring such register space. When the facility is installed, the bits
perform thedefined control function.
TheLOAD CONTROL instruction causes all
control-register positions within those
registers designated by the instruction
to be loaded from storage. The
instructionsLOAD ADDRESS SPACE PARAME TERS, SET SECONDARY ASN, PROGRAM CALL, and PROGRAM TRANSFER provide specialized functions to place information into
certain control-register positions.
Information loaded into the control
registers becomes active (that is,
assumes control over the system) at the
completion of the instruction causing
the information to be loaded.
At the time the registers are loaded,
the information is not checked for
exceptions, such as invalid
translation-format code or an address
designating an unavailable ora protected location. The validity of the
information is checkedand the exceptions, if any, are indicated at the time the information is used. The STORE CONTROL instruction causes all
control-register positions, within those
registersdesignated by the instruction,
to be placed instorage. The
instructionsEXTRACT PRIMARY ASN, EXTRACT SECONDARY ASN, and PROGRAM CALL provide specialized functions to obtain information from certain control
registerpositions. Values corresponding to unassigned or unin
stalled register positionsare unpredictable. Only the general structure of the
control registers is described here; the
definition ofa particular control
register position appears in the
description of the facility with which
the register position is associated.
The figure "Assignment ofControl Register Fields" shows the control
register positions which are assigned
and the initial value of the field upon
execution ofinitial CPU reset. Programming Notes
1. The detailed definition ofa particular control-register bit
positioncan be located by refer
ring to the entry "control-registerassignment" in the Index.
2. To ensure that existing programs
operate correctly if and whennew facilities using additional
control-register positions are
installed, the program shouldload zeros in unassigned control
register positions. AlthoughSTORE CONTROL may provide zeros in the
bit positions corresponding to
unassigned or uninstalled register
positions, the program should not
depend on suchzeros. It is
permissible, however, for theprogram to load into the control
registers any information previous
ly stored bymeans of STORE CONTROL. Chapter 4. Control 4-9
to
control registers are assigned to
perform the
The
control-register positions within those
registers designated by the instruction
to be loaded from storage. The
instructions
certain control-register positions.
Information loaded into the control
registers becomes active (that is,
assumes control over the system) at the
completion of the instruction causing
the information to be loaded.
At the time the registers are loaded,
the information is not checked for
exceptions, such as invalid
translation-format code or an address
designating an unavailable or
information is checked
control-register positions, within those
registers
to be placed in
instructions
register
stalled register positions
control registers is described here; the
definition of
register position appears in the
description of the facility with which
the register position is associated.
The figure "Assignment of
register positions which are assigned
and the initial value of the field upon
execution of
1. The detailed definition of
position
ring to the entry "control-register
2. To ensure that existing programs
operate correctly if and when
control-register positions are
installed, the program should
register positions. Although
bit positions corresponding to
unassigned or uninstalled register
positions, the program should not
depend on such
permissible, however, for the
registers any information previous
ly stored by
