Spectravideo SVI 318 Service – Technical Manual page 37

( 3 )
Two I nd e x R eg i s t e r s ( IX and I Y ) .
The t wo i n d e p e n d e n t i n d e x r e g i s t e r s ho l d a 1 6-b i t ba s e a d d r e s s t ha t is
u se d in inde x e d a dd r e s s in g mod e s .
us e d a s a ba s e t o po i n t t o a re g i on i n memory f rom wh i c h da t a i s t o be
s t o re d or r e t r i e ve d.
in s t r uc t i on s t o s p e c i f y a d i sp l a ceme n t i s s p e c i f i e d a s a t wo ' s comp l e ­
me n t s i g ne d i n t e ge r.
t yp e s o f p r o g ramme s , e sp e c i a l l y whe r e tab l e s of data a r e use d .
I n t e rrupt Page A dd r e s s Reg i s t e r ( I ) .
( 4 )
The Z-80 CPU c a n be ope r a t e d in a mode whe r e an ind i re c t ca l l t o any
memory l oc a t i on c an be ach i eve d in r e s ponse to an i n t e r r up t .
Reg i s ter i s u s e d f or th i s pu r p o s e to s t o re the h igh o r d e r 8-b i t s o f
t he ind i r e c t a dd r e ss wh i l e t he i n t e r r up t ing dev i ce p ro v i d e s the l ow e r
8-b i t s o f the a dd re s s .
d y n am i c a l ly l oc a te d an ywhe re in memory w i th a b s o l u te m i n i ma l a c c e s s
t i me t o t h e rou t i ne .
INTERRUPT
VECTOR
I
INDEX R E G I S T E R IX
I N DEX R E G I S T E R IY
STACK POINTER S P
P ROGRANHE C OUNTER P C
Z-80 CPU REGI STER CONFIGURATION
F ig. 4-3
An a dd i t i on a l byte i s i nc l ud e d in i n de x e d
Th i s mod e o f a dd r e s s ing g r e a t ly s imp l i f i e s many
T h i s fea t u re a l l ows int e r r u p t rou t i n e s t o be
MEMORY
REFRESH
R
In t h i s mo d e , an i n d e x r e g i s t e r i s
The I
. �