THE
80286
INSTRUCTION
SET
SAL/SARISHL/SHR-Shift
Instructions
Opcode Instruction Clocks-N'
Description
DO
/4
SAL
eb,1
2,mem=7
Multiply
EA
byte
by
2,
once
02
/4
SAL eb,CL
5,mem=8
Multiply
EA
byte
by
2,
CL times
CO
/4
db SAL eb,db
5,mem=8
Multiply
EA
byte by
2,
db times
01
/4
SAL
ew,1
2,mem=7
Multiply
EA
word
by
2,
once
03
/4
SAL ew,CL
5,mem=8
Multiply
EA
word
by
2,
CL times
C1
/4
db SAL ew,db
5,mem=8
Multiply
EA
word
by
2,
db times
DO
/7
SAR
eb,1
2,mem=7
Signed divide
EA
byte by
2,
once
02
/7
SAR eb,CL
5,mem=8
Signed divide
EA
byte
by
2,
CL times
CO
/7
db SAR eb,db
5,mem=8
Signed divide
EA
byte by
2,
db times
01
/7
SAR
ew,1
2,mem=7
Signed divide
EA
word
by
2,
once
03
/7
SAR ew,CL
5,mem=8
Signed divide
EA
word
by
2,
CL times
C1
/7
db SAR ew,db
5,mem=8
Signed divide
EA
word
by
2,
db times
DO
/5
SHR
eb,1
2,mem=7
Unsigned divide
EA
byte
by
2,
once
02
/5
SHR eb,CL
5,mem=8
Unsigned divide
EA
byte
by
2,
CL times
CO
/5
db
SHR eb,db
5,mem=8
Unsigned divide
EA
byte
by
2,
db times
01
/5
SHR
ew,1
2,mem=7
Unsigned divide
EA
word
by
2,
once
03
/5
SHR ew,CL
5,mem=8
Unsigned divide
EA
word
by
2,
CL times
C1
/5
db
SHR ew,db
5,mem=8
Unsigned divide
EA
word
by
2,
db times
* Add 1 clock to the times shown for each shift performed
FLAGS
MODIFIED
Overflow (only for single-shift form), carry, zero, parity, sign
FLAGS
UNDEFINED
Auxiliary carry; also overflow for multi bit shifts (only).
OPERATION
SAL (or its synonym SHL) shifts the bits of the operand upward. The high-order bit
is
shifted into the
carry flag, and the low-order bit
is
set to
O.
SAR
and
SHR
shift the bits of the operand downward. The low-order bit
is
shifted into the carry flag.
The effect
is
to divide the operand by
2.
SAR
performs a signed divide: the high-order bit remains the
same.
SHR
performs an unsigned divide: the high-order bit
is
set to
O.
The shift
is
repeated the number of times indicated
by
the second operand, which
is
either an immedi-
ate number or the contents of the CL register.
To
reduce the maximum execution time, the 80286 does
not allow shift counts greater than
31.
If
a shift count greater than
31
is
attempted, only the bottom
five bits of the shift count are used. The 8086 uses all 8 bits of the shift count.
The overflow flag
is
set only if the single-shift forms of the instructions are used. For left shifts,
it
is
set
to
0 if the high bit of the answer
is
the same
as
the result carry flag
(Le.,
the top
two
bits of the
original operand were the same); it
is
set
to
1 if they are different. For
SAR
it
is
set to 0
for
all single
shifts. For SHR, it
is
set to the high-order bit of the original operand. Neither flag bit
is
modified when
the count value
is
zero.
8-97
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