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SILICON GATE MOS
8080
A
INSTRUCTION SET
The
accumulator
group
instructions include arithmetic and
logical
operators
with
direct,
indirect, and immediate ad-
dressing modes.
Move, load, and·
store
instruction groups provide
the
ability
to
move
either
a
or
16
bits
of
data
between memory,'
the
six working registers and
the
accumulator
using direct,
in-
direct, and
'immediate
addressing modes.
The
ability
to
branch
to
different
portions
of
the
program
is
provided with
jump,
jump
conditional, and
computed
jumps. Also
the
ability
to
call
to
and
return
from sub-
routines
is
provided
both
conditionally
and
unconditionally.
The
RESTART
(or
single
byte
call instruction)
is
useful
for
interrupt
vector
operation.
OOl:Jble
precision
operators
such as stack manipulation and
double
add
instructions
extend
both
the
arithmetic
and
interrupt
handling capability
of
the
a080A.
The
ability
to
increment and
decrement
memory,
the
six general registers
and
the
accumulator
is
provided as well as
extended
incre-
ment
and
decrement
instructions
to
operate
on
the
register
pairs and stack pointer.
Further
capability
is
provided by
the
ability
to
rotate
the
accumu
lator
I~ft
or
right
through
or
around
the
carry bit.
Input
and
output
may be accomplished using
memory
ad-
dresses as I/O
ports
or
the
directly
addressed I/O provided
for
in
the
8080A
instruction set.
The
following special
instruction
group
completes
the
8080A
instruction set:
the
NOP instruction, HALT
to
stop
pro-
cessor
execution
and
the
OAA instructions provide decimal
arithmetic capability. STC allows
the
carry
flag
to
be di-
rectly set, and
the
CMC
instruction allows it
to
be comple-
mented. CMA
complements
the
contents
of
the
accumulator
and
XCHG exchanges
the
contents
of
two
16-bit register
pairs directly.
Data and Instruction Formats
Data in
the
a080A
is
stored
in
the
form
of
a-bit
binary integers. All
data
transfers
to
the
system
data
bus
will be in
the
same
format.
1
0
7
06
Os
04
03
02
01
001
OATA WORO
The
program instructions may be
one,
two,
or
three
bytes
in
length. Multiple
byte
instructions
must
be stored
in
successive words
in
program memory.
The
instruction formats
then
depend
on
the
particular
operation
executed.
One
Byte Instructions
Two
Byte Instructions
1
0
.
7
06
Os
D4
°3
°2
°1
DO
I
OP CODE
1
0
7
°6
Os
D4
°3
°2
°1
DO
I
OPERANO
Three
Byte Instructions
1
0
7
°6
Os
04
°3
°2
°1
DO
I
OP COOE
1
0
7
°6
Os
04
°3
°2
0
1
DO
I
LOW
ADDRESS OR OPERAND 1
1
0
7
06
Os
04
03
°2
°1
DO
I
HIGH ADDRESS OR OPERANO 2
TYPICAL INSTRUCTIONS
Register
to
register,
memory
refer-
ence, arithmetic
or
logical,
rotate,
return, push,
pop,
enable
or
disable
I
nterrupt
instructions
Immediate
mode
or
I/O instructions
Jump,
call
or
direct
load and
store
instructions
For
the
8080A
a logic
"1"
is
defined as a high level and a logic
110"
is
defined
as a low level.
6-18