in~.
MCS@-51PROGRAMMER’SGUIDE AND INSTRUCTIONSET
DJNZ <byte>, <rel-addr>
Function: DecrementandJumpif Not
=0
Description: DJNZ decrementsthe locationindicatedby 1,andbranchesto the addressindicatedby the
secondoperandif the resultingvalueis not zero. An originalvalueof OOHwillunderflowto
OFFH.No tlagsare at%cted.Thebranch destinationwouldbe computedbyaddingthe signed
relative-displacementvaluein the last instructionbyteto the PC, afterincrementingthe PC to
the first byte ofthe followinginstruction.
The locationdecreznentedmaybe a registeror directlyaddressedbyte.
Note:When
thisinstructionis used to modfi an outputport, the valueusedas the original
port data willbe readfrom the output data latch, notthe input pins.
Example: Internal RAM locations40H, 50~ and 60Hcontainthe valuesOIH,70H,and 15H,respec-
tively.The instructionsequence,
DJNZ 40H,LABEL-1
DJNZ 50H,LABEL-2
DJNZ 60H,LABEL-3
willcauseajumpto the instructionat labelLABEL-2 withthe valuesOOH,6FH,and 15Hin
the three W locations The firstjump wasnottakenbecausethe result waszero.
This instructionprovideaa simplewayof executinga programloopa givennumberof times,
or for addinga moderatetime delay (from2 to 512machinecycles)witha singleinstruction.
The instructionsequence,
MOV R2,#8
TOOOLE: CPL P1.7
DJNZ
R2,TOOGLE
will toggleP1.7 eighttimes, causingfour output pukes to appear at bit 7 of output Port 1.
Each pulsewilllast three machinecycles;two for DJNZ and oneto alter the pin.
DJNZ Rn,rel
Bytee: 2
cycles: 2
Encoding:
I
1101
11’”1 EEl
Operation:
DJNZ
(PC!)- (PC) + 2
m) -(w – 1
w ~~~ 0 or (I@ < t)
(PC)+ (PC)+ rd
2-43
To Next Page
Loading...
Need help?
General
