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STORE CHARACTER
STC
R1,02(X2,B2)
[RX]
1421
I
R 1
I
X2
I
B2
°2
0
8
12
16
20
31
Bits 24-31 of the general register designated by the
R
1
field are placed unchanged at the
.
second-operand location. The second operand
IS
one byte in length.
Condition Code: The code remains unchanged.
Program Exceptions:
Access (store, operand 2)
STORE CHARACTERS UNDER MASK
I
BE
I
I
R 1
I
M3
I
B2
I
02
o
8
12
16
20
31
Bytes selected from the first operand under control
of a mask are placed in contiguous byte locations
beginning at the second-operand address.
The contents of the M3 field are used as a mask.
These four bits, left to right, correspond one for
one with the four bytes, left to right, of the general
register designated by the R
1
field. The bytes
corresponding to ones in the mask are placed in the
same order in successive and contiguous storage
locations beginning at the second-operand address.
When the mask is not zero, the length of the
second operand is equal to the number of ones in
the mask. The contents of the general register
remain unchanged.
When the mask is not zero, exceptions associated
with storage-operand accesses are recognized only
for the number of bytes specified by the mask.
When the mask is zero, the single byte
designated by the second-operand address remains
unchanged; however, on some models, the value
may be fetched and subsequently stored back at the
same storage location. No access by another CPU
is permitted to the location designated by the
second-operand address between the moment that
the value is fetched and the value is stored.
Condition Code: The code remains unchanged.
7-32
IBM 4300 Processors Principles of Operation
Program Exceptions:
Access (store, operand 2)
Programming Notes
1. An example of the use of STORE
CHARACTERS UNDER MASK is given in
Appendix A.
2. STCM with a mask of
a
111 may be used to
store a three-byte address, for example, in
modifying the address in a CCW.
3. STCM with a mask of 1111, 0011, or 0001
performs the same function as STORE (ST),
STORE HALFWORD (STH), or STORE
CHARACTER (STC), respectively. However,
on most models, the performance of STCM will
be slower.
4. Using STCM with a zero mask should be
avoided since this instruction, depending on the
model, may perform a fetch and store of the
single byte specified by the second-operand
address. This access is not interlocked against
accesses by channels. In addition, it may cause
any of the following to occur for the byte
specified by the second -operand address: a
PER storage-alteration event may be
recognized; access exceptions may be
recognized; and, provided no access exceptions
exist, the change bit may be turned on.
STORE CLOCK
STCK
[S]
I
B2 0 S
1
°2
o
16
20
31
The current value of the time-of-day clock is stored
at the eight-byte field designated by the
second-operand address, provided the clock is in
the set or not-set state.
Zeros are stored for the rightmost bit positions
that are not provided by the clock.
Zeros are stored at the operand location when
the clock is in the error state or in the
not-operational state.
The quality of the clock value stored by the
instruction is indicated by the resultant
condition-code setting.
A serialization function is performed before the
value of the clock is fetched and again after the
value is placed in storage. CPU operation is
delayed until all previous accesses by this CPU to
(
I
~
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