Spectravideo SVI 318 Service – Technical Manual page 73

The S p r i t e P l a n e s a re u s e d f o r t h e 3 2 s p r i t e s in t h e Mu l t i c o l o u r a n d
3 2
Gra p h i c s mod es . The y a r e no t u s e d i n t h e T e x t mode a n d a r e a u toma t i c a l l y
t r a n s p a re n t . E ac h of t h e s p r i t e s c an c o v e r
a r e a on i t s p l a n e .
pa re nt . A l l or pa r t of e a c h s p r i t e ma y a l s o
t h e ou t s i d e o r h i gh e s t p l a n P , a n d sp r i t e
a d j a c e nt t o Pa t t e rn P l a n e .
t h e co l ou r of t h e ne x t p l a n e c a n be s e e n t h r o u g h t h a t p l ane .
sp r i t e p i x e l is non- t r a n s p a r e n t , t he c o l ou r s
ca l l y re p l a c e d by the sp r i t P co l o u r .
o f s p r i t e s on a l i ne .
Add i t i o n a l sp r i t e s on a l i n e w i l l be a u t oma t i c a l l y made t r a n s p a r e n t f o r tha t
l i ne . On ly t ho s e sp r i t e s t h a t a re a c t i ve
co i n c i d en c e f l ag t o s e t .
numb e r o f t he f i f t h s p r i t e whe n e v e r t h i s o c cu r s .
the T e x t , Mu l t i c o l ou r , and G raph i c s m o d e s
o f cha r a c t e rs . Wh e ne v e r a p i x e l on t h e P a t t e rn P l a ne i s non- t r a n s p a r e n t , t h e
ba ckd rop co l o u r i s a u t oma t i c a l l y rep l a c e d by t h e Pa t t e r n P l a n e co l ou r .
p i xe l in t he Pa t t e rn P l a ne i s t ra n s p a r en t , t he b ackd rop c o l ou r c a n be s e e n
t h r o ugh t h e Pa t t e rn p l a n e .
The VDP ha s fou r v i d ed c o l o u r d i s p l a y mo d e s t h a t appe a r on the P a t t e rn P l ane :
G r ap h i c s I mode , G r aph i c s
and G raph i c s I I mo d e s c a u s e t h e Pa t t e rn P l a n e to be brok e n up i n t o g ro u p s o f
8 x 8 p i x e l s , c a l l e d p a t t e rn p o s i t i o ns .
p i xe l s , t h e r e a r e 3 2
In G r ap h i c s I mod e , 2 5 6 p o s s i b l e p a t t e r ns may be de f i n e d f o r the 7 6 8 pa t t e rn
p o s i t i o n s wi t h t wo un ique c o l o u r s a l l owe d f o r each pa t t e r n de f i n i t i o n .
mode p rov i d e s , t h rough a un i que m a p p ing s c h eme ,
G r aph i c s
I I
d e f i n a t i o n s for the 7 6 8 pa t t e rn po s i t i ons .
se l e c t i on o f two u n i q�e co l ou r s for e ac h l i ne o f a p a t t e rn de f i n i t i on .
a l l 1 5 co l ou rs p l u s t u ans p a r e n t ma y be u s e d in a s i n g l e pa t t e rn p o s i t i o n .
T e x t mod e , t he P a t t e rn P l a ne i s b roken i n t o g r ou p s o f
po s i t i o n s . The r e a r e 40
Te x t mode , sp r i t e s do n o t appe a r on t he s c r e e n and t wo c o l ou r s are d e f ined f o r
t h e e n t i r e s c r e e n .
6 4 x p o s i t i o ns , e a¢h o f wh i c h i s a 4 x 4 p i xe l .
48
is
un ique c o l o u r a l l owe d .
rhe V DP reg i s t e r s de f i ne th e ba se a dd r e s s e s f o r s e ve r a l sub-b l oc k s w i t h i n VRAM .
The s e sub-b l oc k s f o rm t ab l e s wh ich a re u s e d t o p roduce t he de s i re d i mage on the
TV sc r e e n .
The Pa t t e tn Name Tab l e , the P a t t e r n Gene ra t o r Tab l e and the S p r i t e
G e ne r a t or T ab l e a re u � e d t o f o rm t he s p r i t e s .
mus t a l l b e p ro v i d e d b y the m i c r o p ro ce s s o r .
VRAH
t he c o n t e n t s o f
Any p a r t o f t h e p l a n e no t cove r e d by t h e sp r i t e i s t r a n s ­
Wh e n e v e r a p i x e l i n a S p r i t e P l a ne i s t r a n s p a r e n t ,
On l y f ou r sp r i t e s c a n
The VDP s t a t u s r e g i s t e r p rov i d e s a f l a g b i t and the
mod e , T e x t mo d e , and M u l t i c o l ou r mod e .
I I
x
3 4 pa t t e rn po s i t i on s on t h e s c r e e n i n the g raph i c mode s .
x
2 4 t e x t p o s i t i on s on t h e s c r e e n i n th i s mode .
I n Mul t i c o l ou r mode , t h e s c r e e n i s b r o k e n i n t o a g r i d o f
ln
re a l t i me .
4 . 4 0
an
1 6
8
x 8 ,
be
t r a n s p a r e n t .
i s o n t h e p l a n e imme d i a t e l y
3 1
o f
t he l ow e r p l a n e s a re a u t om a t i ­
The r e i s a l s o a r e s t r i c t i o n on the numbe r
be
a c t i ve on any h o r i z o n t a l l ine .
on
t he d i s p l a y w i l l c a u s e the
The Pa t t e rn P l a ne i s u s e d in
fo r
d i s p l a y o f t h e g ra p h i c p a t t e r n s
S i n c e t he fu l l i ma g e i s 2 56 x 1 9 2
G r ap h i c s I I mode a l s o a l l ow s the
6
W i th i n e a ch p o s i t i on , one
T he c o n t e n t s o f t h e s e t ab l e s
Anima t i on i s ach i e v e d by a l t e r i ng
1 6 ,
x or 3 2 x 3 2 p ix e l
S p r i t e 0 i s o n
I f , howeve r , the
W h e n a
G r aph i c s I
7 6 8
p a t t e rn
Thus ,
x 8 p i x e l s , c a l l e d t e x t
I n
I n