Set Psw Key From Address - IBM 4300 Manual

associated with the storage page designated by the
second-operand address are replaced by the
contents of the general register'designated by the
Rl field.
Bits 8-20 of the second-operand address
designate the page. Bits 0-7 and 21-31 of the
address are ignored. Bits 12-15 of the instruction
are ignored.
The condition code is set to reflect the state of
the reference and change bits before these bits are
modified.
The new values of the three page bits are
obtained from bit positions 25-27, and the
reference and change bits from bit positions 29-30
of the register designated by the R
1
field. The
contents of bit positions 0-24, 28, and 31 of the
register are ignored.
The references to the page bits and to the
reference and change bits are not subject to a
protection exception. These bits can be accessed
regardless of the state of the addressed page.
Resulting Condition Code:
o
Reference bit zero, change bit zero
1 Reference bit zero, change bit one
2 Reference bit one, change bit zero
3 Reference bit one, change bit one
Program Exceptions:
Addressing (operand
2)
Privileged Operation
SET PSW KEY FROM ADDRESS
'B20A'
o
16
20
31
The four-bit PSW key, bits 8-11 of the current
PSW, is replaced by bits 24-27 of the
second-operand address.
The second-operand address is not used to
address data; instead, bits 24-27 of the address
form the new PSW key. Bits 8-23 and 28-31 of
the second-operand address are ignored.
Condition Code: The code remains unchanged.
Program Exceptions:
Privileged Operation
10-10 IBM 4300 Processors Principles of Operation
Programming Notes
1. The format of the SET PSW KEY FROM
ADDRESS instruction permits the program to
set the PSW key either from the general
register designated by the B2 field or from the
D2 field in the instruction itself.
2. When a problem program requests a control
program to access a location specified by the
problem program, the SET PSW KEY FROM
ADDRESS instruction can be used by the
control program to verify that the problem
program is authorized to make this access,
provided the storage location of the control
program is not protected against fetching. The
control program can perform the verification by
replacing thePSW key of the control program
with the problem-program PSW key before
making the access and subsequently restoring
the control-program PSW key to its original
value.
SET STORAGE KEY
SSK Rl,R2 [RR]
'08' R1
I
R2
I
o
8 12 15
The storage key associated with the page that is
addressed by the contents of the general register
designated by the R2 field is replaced by the
contents of the general register designated by the
Rl field.
Bits 8-20 of the register designated by the R2
field designate the page. Bits 0-7 and 21-27 of the
register are ignored. Bits 28-31 of the register
must be zeros; otherwise, a specification exception
is recognized, and the operation is suppressed.
The new seven-bit storage-key value is obtained
from bit positions 24-30 of the register designated
by the Rl field. The contents of bit positions 0-23
and 31 of the register are ignored.
The reference to the storage key is not subject to
a protection exception. The storage key can be
accessed regardless of the state of the addressed
page.
Condition Code: The code remains unchanged.
Program Exceptions:
Addressing (operand
2)
Privileged Operation
Specification