it@l.
MCS’@-51PROGRAMMER’SGUIDE AND INSTRUCTION SET
CJNE <dest-byte>,<src-byte>,rel
Function:
Description:
Compareand Jump if Not Equal.
CJNEcomparesthe magnitudesofthe fmt twooperands,andbranchesif their valuesare not
equal.The branch destinationis computedby addingthe signedrelative-displacementin the
last instructionbyte to the PC, after incrementingthe PC to the start of the nextinstruction.
The carry flag is set if the unsignedintegervalueof <dest-byte> is less than the unsigned
integervalueof <src-byte>; otherwise,the carry is cleared.Neither operandis tided.
The first two operandsallow four addressingmodecombinations:the Accumulatormay be
comparedwithany directlyaddressedbyteor immediateda~ andanyindirectRAMlocation
or worldngregister can be comparedwithan immediateconstant.
The Accumulator contains 34H. Register 7 contains 56H. The first instruction in the se-
quence
CJNE R7,#60H, NOT-EQ
. . . . . ; R7 = 60H.
NOT—EQ: “‘“
JC
REoLLOw
; IF R7 < &3H.
. .. . . . . .
; R7 > 60H.
setsthecarryflagandbranchesto the instructionat labelNOT-EQ. Bytestingthe carry flag,
this instructiondetermines whetherR7 is greater or lessthan 60H.
If the data beingpresentedto Port 1is also 34H,then the instruction,
WAIT: CJNE A,P1,WAIT
clearsthe carry tlag and continueswiththe nextinstructionin sequence,sincetheAccumula-
tor doesequalthe data read fromP1.(If someothervaluewasbeinginputon Pl, theprogram
willloopat this point until the PI data changesto 34H.)
CJNE A,direct,rel
Bytes: 3
Cycles: 2
Encoding:
1o11
0101
I ‘ire”addressI EiEl
Operation:
(PC) - (PC) + 3
IF (A) <> (direct)
THEN
(PC)+ (PC) + relativeoffket
IF (A) <
(direct)
THEN
~L~E (c) -1
(c)+ o
2-35
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