Special Purpos E Registers - Spectravideo SVI 318 Service – Technical Manual

CPU RESGISTERS
T he Z-80 CPU �o n t a i n s 20 8 b i t s o f
p rog ramme r . F i gu re
e i gh t e e n 8-b i t re g t e r s an d fou r 1 6-b i t r e g i s t e r s .
impl emen t e d us i n g s t a t i c
g e n e r a l p u r p o s e reg i s t e r s that ma y b e us e d i n d i v i d u a l l y a s 8-b i t re g i s t e r s
o r i n pa i r s a s 1 6 -bi t re g i s t e r s .
a n d f la g reg i s t e rs .

SPECIAL PURPOS E REGISTERS

( 1 ) P ro g r amme Coun t e r ( PC ) .
The p ro g ramme cou n t e r ho l d s the 1 6-b i t a dd re s s o f the c u r r e n t
i n s t r u c t i on b e ing f e t che d f rom memo r y .
increme n t e d a f t e r i t s con t e n t s have been t r a n s f e r r e d to t h e a dd r e s s
l i n e s . Wh e n a p r o g r amme j ump occu r s t he new va l ue i s a u toma t i c a l l y
p l a c e d in the PC , ove r r i d i ng
( 2 ) S t ack P o i n t e r ( S P ) .
The s t a ck po i n t e r ho l ds the 1 6-b i t a dd re s s o f the c u r r e n t top o f a
s t ack l oc a t e d anywhe re in ex t e rn a l s y s t em RAM memory .
s t ack memo r y i s o r i g an i z e d a s a la s t- i n f i r s t - ou t ( L I FO ) f i l e .
c a n b e p u s he d o n t o t he s t ack f rom s p e c i f ic C P U reg i s t ers o r p o p p e d o f f
o f t h e s t ack in t o s p e c i f i c CPU reg i s t e r s th rough the e
and POP i n s t r u c t i o ns .
l a s t data p u s h e d on t o i t .
mu l t i p l e l e ve l i n t e r r up t s , un l im i te d s u b r ou t i ne n e s t ing and
s i mp l i f i c a t i on o f many t yp e s of data man i p u l a t i on .
MA IN REG SET
ACCUMULATOR
B
D
H
-
R /W memory tha t a re ac c e s s a b l e to the
i l l us t ra tes how th i s me mory is con f i gu r e d i n t o
4-3
RAM .
The reg i s t e r s inc l u d e t w o s e t s o f s i x
The r e a r e a l s o two se t s o f accumu l a t o r
the incrementer.
The d a ta popped f rom the s t ack i s a lway s t h e
The s t a c k a l l ows s imp l e imp l eme n t a t i o n o f
FLAG S
F
c
E
L
4 . 3
A l l Z-80 r e g i s t e r s a r e
The P C i s a u toma t i c a l ly
ALTERNATE REG SET
ACCUMULATOR FLAGS
A '
B'
D'
H '
The e x t e r n a l
D a t a
�
e c u t i on o f P USH
F '
C '
GENERAL
E '
P URPOSE
REG I STER
L '