Intel 80C186EA User Manual page 372

Name
REP Repeat:
REPE Repeat While Equal:
REPZ Repeat While Zero:
REPNE
Repeat While Not Equal:
REPNZ Repeat While Not Zero:
Controls subsequent string instruction
repetition. The different mnemonics
are provided to improve program
clarity.
REP is used in conjunction with the
MOVS (Move String) and STOS (Store
String) instructions and is interpreted
as "repeat while not end-of-string" (CX
not 0).
REPE and REPZ operate identically
and are physically the same prefix byte
as REP. These instructions are used
with the CMPS (Compare String) and
SCAS (Scan String) instructions and
require ZF (posted by these instruc-
tions) to be set before initiating the
next repetition.
REPNE and REPNZ are mnemonics
for the same prefix byte. These
instructions function the same as
REPE and REPZ except that the zero
flag must be cleared or the repetition is
terminated. ZF does not need to be
initialized before executing the
repeated string instruction.
Instruction Operands:
none
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
ü
the flag is updated after the instruction is executed
Table C-4. Instruction Set (Continued)
Description
INSTRUCTION SET DESCRIPTIONS
Operation
do while (CX) ≠ 0
service pending interrupts (if any)
execute primitive string
Operation in succeeding byte
(CX) ← (CX) – 1
if
primitive operation is CMPB,
CMPW, SCAB, or SCAW and
(ZF) ≠ 0
then
exit from while loop
Flags
Affected
AF –
CF –
DF –
IF –
OF –
PF –
SF –
TF –
ZF –
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