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NPP CPU Architecture, Addressing Modes and Data Transfer Schemes 407

3. CS is pushed on stack. 3. CS ñQ>¡H$ na ^oOm OmVm h¡ &
4. CS is loaded from (4n + 2) and (4n + 3) 4. CS H$mo (4n + 2) VWm (4n + 3) {\${OH$c cmoHo$eÝg
physical locations. H$mo cmoS> {H$`m OmVm h¡&
5. IP is pushed on stack. 5. IP ñQ>¡H$ na ^oOm OmVm h¡&
6. IP is loaded from (4n) and (4n + 1) physical 6. IP H$mo (4n) VWm (4n + 1) {\${OH$c ES´>ogog go cmoS>
addresses. {H$`m OmVm h¡&
Next instruction address is calculated from AJcm BÝñQ´>ŠeZ ES´>og IP VWm CS H$s Z`r d¡ë`y go
new values of IP and CS. This is how the pro- JUZm {H$`m OmVm h¡& Bg H$maU àmoJ«m_ H$ÊQ´>moc Z`o g~éQ>rZ
gram control jumps to a new subroutine. The na Oån H$aVm h¡& Bg g~éQ>rZ H$m àmapå^H$ ES´>og BÝQ>aßQ>
beginning address of this subroutine is called
interrupt vector address and the subroutine is doŠQ>a ES´>og H$hcmVm h¡ VWm g~éQ>rZ H$mo BÝQ>aßQ> g{d©g
called Interrupt service Routine (ISR). éQ>rZ (ISR) H$hm OmVm h¡&
IRET: Interrupt Return; used at the end of IRET: BÝQ>aßQ> [aQ>Z© H$mo H$m°qcJ àmoJ«m_ go dmng
ISR to return to the calling program. AmZo Ho$ {cE ISR Ho$ AÝVa _| Cn`moJ {H$`m OmVm h¡&
Following sequence of operations take Am°naoeÝg H$m {ZåZ{c{IV {gŠd|g ahVm h¡:
place: NPP
1. Two bytes of stack are transferred to IP. 1. ñQ>¡H$ H$s Xmo ~mBQ²>g IP _| Q´>mÝg\$a H$s OmVr h¢&
2. Next to bytes are poped into CS. 2. AmJo H$s ~mBQ> CS _| nm°ßS> H$s OmVr h¢&
3. Next two bytes are poped into flag register. 3. AmJo H$s Xmo ~mBQ²>g âcoJ a{OñQ>a _| nm°ßS> H$s OmVr h¢&
The values of CS and IP points of the CS VWm IP H$s d¡ë`yO BÝñQ´>ŠeZ Ho$ BÝñQ´>ŠeZ h¢
instruction which follows INTn instruction in Omo H$m°qcJ àmoJ«m_ _| INTn BÝñQ´>ŠeZ H$m nmcZ H$aVo h¢&
the calling program. Program control returns
to this next location. àmoJ«m_ H$ÊQ´>moc Bg AJcr cmoHo$eZ H$mo [aQ>Z© H$aVm h¡&
INTO: Interrupt on Overflow, INT4 is ex- INTO: BÝQ>aßQ> Am°Z Amodaâcmo, INT4 EŠOrŠ`yQ>
ecuted whenever OF is set. hmoVm h¡ O~ H$^r OF goQ> hmoVm h¡&

5.4.4 Machine Control Instructions 5.4.4 _erZ H$ÊQ´>moc BÝñQ´>ŠeÝg

STC: Set Carry; used to set CF thus CF = 1 is STC: goQ> Ho$ar H$mo CF goQ> H$aZo Ho$ {cE Cn`moJ {H$`m
obtained. OmVm h¡& Bg àH$ma CF = 1 àmßV hmoVm h¡&
CMC: Complement carry; the value of CF is CMC: H$m°påßc_oÝQ> Ho$ar; CF H$s d¡ë`y H$m°påßc_oÝQ> H$s
complemented. OmVr h¡&

STD: Set direction flag; thus DF = 1 is ob- STD: goQ> S>mBaoŠeZ âcoJ; Bg àH$ma DF = 1 àmßV
tained. hmoVm h¡&

STI : Set Interrupt flag, Thus IF = 1 is ob- STI : goQ> BÝQ>aßQ> âcoJ, Bg àH$ma IF = 1 àmßV hmoVm
tained h¡&

CLC: Clear carry flag, CF = 0 is obtained CLC: Šcr`a Ho$ar âcoJ, CF = 0 àmßV hmoVm h¡&
CLI: Clear Interrupt flag, Thus IF = 0 is ob- CLI: Šcr`a BÝQ>aßQ> âcoJ, IF = 0 àmßV hmoVm h¡&
tained.