i~e MCS”-51 PROGRAMMER’SGUIDE AND INSTRUCTION SET
MUL AB
Deeoriptiors:
Example
Bytes:
Cycles:
Encoding:
Operation:
NOP
Multiply
MUL AB multipliesthe unsignedeight-bit integersitsthe Accumulatorand registerB. The
Iow-orderbyteofthe sixteen-bitproduct is left in the Accumulator,and the high-orderbytein
B. If the product is greater than 255(OPPH)the ovcrtlowflag is set; otherwiseit is cleared.
The carry fiagis alwayscleared.
Originallythe Accumulatorholdsthe value80(50H).RegisterB holdsthe value160(OAOH).
The instruction,
MuLAB
willgivethe product 12,S00(3200H),soB is changedto 32H(OO11OO1OB)andtheAccumula-
tor is cleared.The overflowflagis set, carry is cleared.
1
4
I 101 OIO1OOI
MUL
(A)74 + (A) X (B)
(B)15-8
Function:
Description:
Example:
Bytes
Cycles:
Encoding:
Operation:
No Operation
Executioncontinuesat the followinginstruction.Other than the PC, no registersor flagsare
affected.
It is desiredto producea low-goingouQut pulseonbit 7of Port 2 lastingexactly5cycles.A
simpleSETB/CLRsequencewouldgeneratea one-cyclepulse,so four additionalcyclesmust
be inserted. This may be done (ssauming no interrupts are enabled) with the instruction
SeqUenee,
CLR P2.7
NOP
NOP
NOP
NOP
SETB P2.7
1
1
000010000
NOP
(PC)+ (-PC)+ 1
2-00
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