In
the
descriptions
of
the
byte-string
instructions, the
following
abbreviations
and
terms
are
used:
o Displacement, (1)12-31.
SA
ESA
C
DA
SBS
DBS
Source address, (R)13-31
Effecti ve source address,
[(R)
13
-31
+(1)
12
-31}
3 -31
The
contents
of
bit
positions 13-31
of
register
R
are
added
(right
aligned)
to the
contents
of
bit
posi tions 12-31
of
the
instruction word; the 19
low-
order
bits
of
the
result
are
used as the
effective
source address.
Count,
(Ru1)0_7
Destination address, (Ru1)13_31
Source
byte
string, the byte' string
that
begins with
the
byte
location
pointed
to by
the
19-bit
effec-
tive
source address
and
is C bytes in length (if
R is
0).
Destination
byte
string, the
byte
string
that
begins
with
the
byte
location
pointed
to by the
des-
ti nati on address
and
is always C bytes in
length.
TRAPS
BY
BYTE-STRING INSTRUCTIONS
Byte-string instructions cause a trap
if
either
of
the
addressed
byte
strings come from memory pages
that
are
protected
by
either
access
protection
or
write
locks. A trap also
occurs
if
elther
byte
stdng
is
fully
or
partly
contoi!"'!ed
with!!"'!
mem-
ory
pages
that
are
physically
not
present. A
check
for
these
access
trap
conditions
is made prior to
initiation
of
any
byte
relocation
or
general
register
change.
These tests
are
performed for MOVE
BYTE
STRING and
TRANS
LATE
BYTE
STRING. The source
and
destination
locations
are
tested
for MOVE
BYTE
STRING;
only
the
destination
lo-
cation
is tested for
TRANSLATE
BYTE
STRING,
since
there
is no assurance
that
the
translate
table
wi
II
be
accessed
in
its
entirety
in
the
course
of
execution.
If
an
access
pro-
tection
violation
were to
occur
in trying to
reach
a
byte
in
the
translate
table
or
decimal
digit
strings during
the
course
of
execution,
then
the
instruction would trap and result in
Ci
pCii-tiCilly
executed
condition.
However,
if
the
destina-
tion
byte
string does
overlap
the translation
table,
the
reg-
isters would be restored in such a manner
that
the instruction
could
be restarted
after
the
protection
violation
had
been
corrected.
When a trap occurs resulting in a
partially
executed
instruction, the Register
Altered
indi
cator
wi"
be
set.
88 Byte-String Instructions
MBS
MOVE
BYTE
STRING
(Immediate Displacement,
continue
after
interrupt)
MOVE
BYTE
STRING copies the
contents
of
the source byte
string (left to right)
into
the
destination
byte string.
The
previous
contents
of
the
destination
byte
string
are
de-
stroyed,
but
the
contents
of
the
source
byte
string
are
not
affected
unless the
destination
byte
string overlaps the
source byte string.
When the
destination
byte
string
overlaps
the
source
byte
string,
the
resulting
destination
byte
string
contains
one
or
more
repetitions
of
bytes from the source byte string. Thus,
if
a
destination
byte
string
of
C bytes begins with the
kth byte
of
a source
byte
string (numbering from 1),
the
first
k-1 bytes
of
the source byte string
are
duplicated
in the
destination
byte
string x number
of
times,
where
x =
C/{k-1).
For
example,
if
the
destination
byte
string begins with the
second
byte
of
the
source byte string,
the
first byte
of
the
source
byte
string
is
duplicated
throughout the
destination
byte
string.
If
both byte strings
begin
with
the same
byte
(i.
e.,
k =
1)
and the R
field
of
MBS
is
nonzero,
the
destination
byte
string
is
read
and
replaced
into the same memory locations.
However,
if both
byte
strings begin with the same
byte
and
the R
field
of
MBS
is
zero,
the first byte
of
the
byte
string
is
duplicated
throughout the remainder
of
the byte string
(see
"Case
111",
below).
Affected:
(DBS),
(R),
(Ru1)
(SBS)
-DBS
If
MBS
is
indirectly
addressed,
it
is
treated
as a
nonexistent
instruction.
The
basic
processor
unconditionally
aborts
execution
of
the instruction (at the time
of
operation
code
decoding) and traps to location X'40'
with
the
contents
of
register R
and
the
destination
byte
string
unchanged.
See
"Traps
by Byte String Instructions" (in this
section)
for
other
trap conditions.
Case
I,
even,
nonzero R
fi
e
Id
(Ru
1
=R
+
1)
Contents
of
register
R:
Contents
of
register
R+1:
The source
byte
string begins with the byte location pointed
to by
the
source address in register R plus the
displacement
in
MBS;
the
destination
byte string begins with the byte
lo-
cation
pointed
to by the
destiratior
address in register
R+l.
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