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INSTRUCTION SET DESCRIPTIONS
C-8
CBW Convert Byte to Word:
CBW
Extends the sign of the byte in register
AL throughout register AH. Use to
produce a double-length (word)
dividend from a byte prior to
performing byte division.
Instruction Operands:
none
if
(AL) < 80H
then
(AH) ← 0
else
(AH) ← FFH
AF –
CF –
DF –
IF –
OF –
PF –
SF –
TF –
ZF –
CLC Clear Carry flag:
CLC
Zeroes the carry flag (CF) and affects
no other flags. Useful in conjunction
with the rotate through carry left (RCL)
and the rotate through carry right
(RCR) instructions.
Instruction Operands:
none
(CF) ← 0AF–
CF
DF –
IF –
OF –
PF –
SF –
TF –
ZF –
CLD Clear Direction flag:
CLD
Zeroes the direction flag (DF) causing
the string instructions to auto-
increment the source index (SI) and/or
destination index (DI) registers.
Instruction Operands:
none
(DF) ← 0AF–
CF –
DF
IF –
OF –
PF –
SF –
TF –
ZF –
Table C-4. Instruction Set (Continued)
Name Description Operation
Flags
Affected
NOTE: The three symbols used in the Flags Affected column are defined as follows:
– the contents of the flag remain unchanged after the instruction is executed
? the contents of the flag is undefined after the instruction is executed
the flag is updated after the instruction is executed