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382 Fundamentals of Computers NPP

5.2.5 Autoincrement or Autodecre- 5.2.5 Am°Q>moBÝH«$s_oÝQ> `m Am°Q>mo{S>H«$s_oÝQ> _moS>
ment mode
This mode uses memory words by speci- Bg _moS> _| a{OñQ>g© H$m Cn`moJ hmoVm h¡ Omo _o_moar
fying registers holding indirect address. But ES´>og AnZo A§Xa aIVm h¡Ÿ& `o ES´>og ñdV… KQ> `m ~‹T>
the registers are automatically incremented or
decremented. Consider following 8086 instruc- OmVm h¡Ÿ& 8086 Ho$ {ZåZ {ZX}e H$mo XoImo:
tions.
MOVSB
It stands for "MOVE STRING BYTE". It is BgH$m VmËn`© h¡ "MOVE STRING BYTE'' & Bg_|
used to transfer contents of a memory location
pointed by register SI in Data segment to the SI a{OñQ>a Ûmam ~VmE _o_moar ES´>og H$s g§»`m DI Ûmam
memory location pointed by DI in Extra seg- ~VmE ES´>og na Mcr OmVr h¡& DF (S>m`aoŠeZ âcoJ) Ho$
ment. The contents of SI and DI registers are _mZ Ho$ AZwgma SI d DI ñdV… KQ>Vo `m ~‹T>Vo h¢Ÿ& 8086
automatically incremented or decremented de-
pending upon value of direction flag DF. Some _mBH«$moàmogoga Ho$ Hw$N> Am¡a {ZX}e {ZåZmZwgma h¢:
more examples for 8086 are:
MOVSB
CMPSB,
SCASB,
SCASW,
LODSB,
LODSW
5.2.6 Direct Addressing mode 5.2.6 S>m`aoŠQ> ES´>oqgJ _moS>
The datum to be operated is referenced by Am°naoQ> {H$¶o OmZo dmbm S>oQ>_ H$m _o_moar ES´>og {ZX}e
specifying its memory address directly in the _| grYo-grYo ~Vm {X`m OmVm h¡Ÿ& 8085 Ho$ {ZåZ {ZX}e
operand. Consider following 8085 instruction:
H$mo XoImo:
LDA 80F2H
Contents of memory address 80F2H are _o_moar ES´>og 80F2H H$s g§»`m EŠ`y_wcoQ>a Zm_H$
loaded into the Accumulator. Similarly, con- a{OñQ>a _| cmoS> hmo OmVr h¡& Bgr àH$ma 8086 H$m {ZåZ
sider following 8086 instruction:
{ZX}e XoI§o:
ADD AL, [4219 H]
The effective address is directly specified _o_moar H$m B\o$[ŠQ>d ES´>og (4219H) {ZX}e _| grYo-
in the operand which is (4219H). Few more grYo ~Vm`m J`m h¡Ÿ& 8085 d 8086 _mBH«$moàmogogg© Ho$
examples from 8085 and 8086 microproces-
sors: Hw$N> Am¡a CXmhaU ZrMo {XE JE h¢:
8085 8086
STA 41FFH MOV CH, [6000]
IN 42H ADD AX, [6F 20]
OUT F2H OUT 40H, AL
LHLD 70F2H IN AL, 3FH