INSTRUCTION
FORMATS
RR
FORMAT
RX FORMAT
RS
FORMAT
•
The
five basic
instruction
formats
express, in general
terms,
the
opera-
tion
to
be
performed
as
follows:
RR
=
register-to-register
RX
= register-to-indexed
main
memory
RS = register-to-main memory
SI
=
main
memory
and
immediate operand operation
SS = main memory to
main
memory
The
instruction
subfields
are
defined
as
follows:
Rl1
R
2
,
Ra
- four-bit general
register
designation used
for
an
operand
X
2
-
four-bit
general
register
designation used
for
indexing
B
l
,
B2
-
four-bit
general
register
designation used
for
base
addressing
DI,
D2
- 12-bit displacement
12
- eight-bit immediate operand
Lh
L2
-
four-bit
operand
length
specification
L - eight-bit operand length specification
M - eight-bit
mask
Before executing
the
Load Multiple,
Store
Multiple,
and
the
SS
format
instructions,
an
address look-up is
performed
to
insure
that
all pages
referenced can be utilized.
The
time required
for
this
address
look-up is
in
addition to
regular
staticizing time.
If
T = 1
(70/46
Mode),
the
addi-
tional
time
is required.
If
T = 0 (70/45 Mode), no additional
time
is required.
•
The
contents
of
the
general
register
specified by Rl is
the
first operand.
The
contents
of
the
general
register
specified by
R2
is
the
second operand.
In
floating-point operations,
Rl
designates
the
address
of
the
floating-point
register
that
contains
the
first operand.
R2
designates
the
floating-point
register
that
contains the second operand. The first
and
second
operands
can
be
the
same
and
are
designated by identical Rl
and
R2
addresses.
Op Code
o 7 8 11 12
15
• The contents
of
the
general
register
specified by Rl is
the
first operand.
To obtain
the
address
of
the
second operand,
the
contents
of
the
general
registers
specified
by
X
2
and
B2
are
added to the
D2
field.
In
floating-point
operations, Rl designates
the
floating-point
register
that
contains
the
first operand.
Op Code
o 7 8 11 12 15 16 19
20
31
•
The
RS
format
is used by
shift
instructions,
branching
instructions,
and
load/store
multiple instructions.
Op Code
o 7 8
11 12
15 16
19
20
31
9
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