Page 400 - FUNDAMENTALS OF COMPUTER

400 Fundamentals of Computers NPP

or memory is specified which points to the OmVm h¡& BZS>m`aoŠQ> _moS> _| EH$ a{OñQ>a `m _o_moar {ZYm©[aV
next instruction address (Branch address). H$s OmVr h¡ Omo AJco BÝñQ´>ŠeZ ES´>og (~«mÝM ES´>og) H$mo
B§{JV H$aVr h¡&
Intersegment: This refers to a transfer from BÝQ>agoJ_oÝQ>: `h EH$ goJ_oÝQ> go Xÿgao goJ_oÝQ> _|
one segment to another segment. Both CS and Q´>mÝg\$a H$m gÝX^© XoVm h¡& CS VWm IP XmoZm| _| n[adV©Z
IP are modified. Therefore the operand must hmoVm h¡& Bg{cE Am°naoÝS> H$mo EH$ 32 {~Q> g§»`m H$m
refer to a 32-bit number. Low order 16-bits are
transferred to IP and High order 16-bits are gÝX^© H$aZm Amdí`H$ h¡& cmo Am°S>©a 16 {~Q> IP H$mo VWm
transferred to CS. This type of instruction is hmB Am°S>©a 16 {~Q²>g CS H$mo Q´>mÝg\$a H$s OmVr h¢& Bg
said to work in FAR mode. àH$ma H$m BÝñQ´>ŠeZ FAR _moS> _| H$m`© H$aVm h¡&
CALL r : The contents of specified regis- CALL r : {ZYm©[aV a{OñQ>a Ho$ H$ÝQ>oÝQ²>g IP H$mo
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ter are transferred to IP. The contents of CS Q´>mÝg\$a {H$`o OmVo h¢& CS Ho$ H$ÝQ>oÝQ²>g An[ad{V©V ah|Jo&
would remain unchanged. Therefore this is
Intra segment branching instruction. Bg{cE `h BÝQ´>m goJ_oÝQ> ~«mpÝM¨J BÝñQ´>ŠeZ h¡&
 First the contents of IP are pushed on · gd©àW_ IP Ho$ H$ÝQ>oÝQ²>g ñQ>¡H$ _| ^oOo OmVo h¢&
stack. Next the contents of specified register BgHo$ níMmV² {ZYm©[aV a{OñQ>a Ho$ H$ÝQ>oÝQ²>g IP _| Q´>mÝg\$a
are transferred into IP. NPP
{H$`o OmVo h¢&
e.g. CALL BX
The above Instruction is executed as fol- CnamoŠV BÝñQ´>ŠeZ {ZåZ àH$ma go EŠOrŠ`yQ> hmoVr h¢:
lows:
(IP) (BX)
New value of IP points to a branch ad- IP H$s Z`r d¡ë`y Cgr goJ_oÝQ> _| EH$ ~«mÝM ES´>og H$mo
dress within the same segment (CS unchanged) g§Ho$V H$aVr h¡ (CS An[ad{V©V ahVm h¡)& `h BZS>m`aoŠQ>
This is indirect Intrasegment branch instruc-
tion because a register gives value of IP. BÝQ´>mgoJ_oÝQ> ~«mÝM BÝñQ´>ŠeZ h¡ Š`m|{H$ EH$ a{OñQ>a IP
H$s d¡ë`y XoVm h¡&
CALL m : m refers to a memory loca- CALL m : m EH$ _o_moar cmoHo$eZ H$m gÝX^©
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tion which points to two bytes (16-bit word). XoVm h¡ Omo Xmo ~mBQ²>g (16 {~Q> dS>©) H$mo B§{JV H$aVm h¡& `h
This word is transferred to IP. CS remain un-
changed. Therefore it is an example of dS>© IP H$mo Q´>mÝg\$a {H$`m OmVm h¡& CS An[ad{V©V ahVm
Intrasegment branch. h¡& Bg{cE `h BÝQ´>mgoJ_oÝQ> ~«mÝM H$m EH$ CXmhaU h¡&
 Previous value of IP is first saved into · IP H$s {nN>cr d¡ë`y nhco ñQ>¡H$ _| god H$s OmVr h¡&
stack.
e.g. CALL [SI]
Two bytes from [SI] and [SI + 1] in data S>mQ>m goJ_oÝQ> _| [SI] VWm [SI + 1] go Xmo ~mBQ²>g IP
segment are transferred to IP. This is a memory _| Q´>mÝg\$a H$s OmVr h¢& `h EH$ _o_moar BZS>m`aoŠQ> BÝñQ´>m
indirect instra segment branch instruction.
goJ_oÝQ> ~«mÝM BÝñQ´>ŠeZ h¡&
CALL d : Call at a 16-bit signed displace- CALL d : EH$ 16 {~Q> gmBÝS> {S>gßcog_oÝQ> na
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ment. This displacement is added to IP. CS re- H$m°c H$aVr h¡& `h {S>gßcog_oÝQ> IP _| Omo‹S> OmVm h¡& CS