Spectravideo MKI, Service – Technical Manual

Page: 73 / 134

The
3 2
S p r i t e P l anes a re u s e d f o r the 3 2 s p r i t e s in the Mu l t i co l our and
Gra p h i c s modes . The y a r e no t used i n the Text mode and are a u toma t ica l l y
t r an s pa re nt . E ach of t h e sp r i t e s c an cover
an
8
x 8 ,
1 6
x
1 6 ,
or 3 2 x 3 2 p ixe l
a r e a on i t s p l a n e . Any p a r t o f the p l ane no t cove r e d by the sp r i t e i s trans­
pa re nt . A l l or pa r t of e a c h spr i te ma y a l s o
be
t ra n s p a r e n t . Sp r i te 0 is on
the ou t s i d e o r h i ghe s t p l a nP , and sp r i t e
3 1
i s on the p l a ne imme d i a te l y
a d j ace nt t o Pa t t e rn P lane . Whenever a p i xe l i n a S p r i t e P l a ne i s t ransparent ,
the co l ou r of the ne x t p l a n e can be s e e n through that p l ane . I f , howeve r , the
sp r i t e p i x e l is non-t ranspa ren t , t he c o l ou r s
o f
t he low e r p l a nes a re au tom a t i­
ca l l y re p l a c e d by the sp r i t P co l ou r . The re i s a l s o a r e s t r i c t ion on the numbe r
o f sp r i t e s on a l i ne . On ly f ou r sp r i t e s c a n
be
ac t i ve on any hor i z on t a l l ine .
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 automa t i c a l l y made t ra n s p a r e n t for 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
on
t he d i s p l ay w i l l cause the
co inc i d ence f l ag to se t . The VDP s t a t u s reg i s t e r p rov i d e s a f l a g b i t and the
numb e r of t he f i f th spr i t e whe never t h i s occu rs . The Pa t t e rn P l a ne i s u s e d in
the Tex t , Mu l t i c o l ou r , and G raph i c s modes
fo r
d i s p l a y of t h e g rap h i c pat t e rns
o f cha r a c t e rs . Whenever a p i x e l on the P a t t e rn P l a ne i s non- t r a nspa re n t , the
ba ckd rop co l ou r i s automa t i c a l l y rep l a c e d by t h e Pa t t e rn P l ane co l ou r . When a
p i xe l in the Pa t t e rn P la ne i s t ransparen t , t he b ackd rop c o l ou r can be seen
through the Pa t t e rn p l a ne .
The VDP ha s fou r v i d ed co lour d i s p l a y mod e s t h a t appe a r on the Pa t t e rn P l ane :
G r ap h i c s
I
mode , G r aph i c s
I I
mod e , Text mod e , and Mu l t i c o l ou r mod e . G raph ics I
and G raph i c s
I I
modes c a u s e the Pa t t e rn P l ane to be broken up i n t o g roups o f
8 x 8 p i x e l s , ca l l e d pat t e rn p o s i t i ons . S i n ce t he fu l l i ma g e i s 2 56 x 1 92
p i xe l s , there a r e 3 2
x
3 4 pa t t e rn po s i t i on s on the s c r e e n i n the g raph ic modes .
In
G r aph i cs I mod e , 2 56 pos s i b l e pat t e rns may be de f ined for the 768 pa t t e rn
p o s i t i ons wi t h two un ique co lours a l l owe d for each pa t t e r n de f in i t i on .
G r aph i c s
I I
mode p rov id e s , t h rough a un ique mapp ing scheme ,
768
pa t t e rn
d e f i na t i o ns for the 768 pa t t e rn po s i t ions . G rap h ic s I I mode a l s o a l l ow s the
se l e c t i on of two uniq�e co l ou rs for e ach l i ne of a pa t t e rn de f i n i t i on . Thus ,
a l l 1 5 co l ou rs p l us t u anspa rent ma y be u s e d in a s in g l e pa t te rn pos i t ion . In
Text mod e , t he P a t t e rn P l ane i s broken i n to g r oups of
6
x 8 p ixe l s , c a l l e d text
po s i t i ons . The re are 40
x
2 4 text po s i t i on s on the screen in th i s mode . In
Tex t mode , sp r i t e s do not appe ar on t he s c r e en and two c o l ou r s are de f ined for
the ent i re s c r e e n . I n Mul t i c o l ou r mode , t h e s c r e e n i s broken i n t o a g r i d o f
64 x
48
pos i t i o ns , e a¢h o f wh ich i s a 4 x 4 p ixe l . W i th in each p o s i t i on , one
un ique c o lou r
is
a l l owed .
rhe VDP reg is t e r s de f i ne th e ba se add r e s s e s for seve ra l sub-b l ocks w i t h in VRAM .
The se sub-b l ocks f o rm t ab l es wh ich a re used to p roduce the de s i re d image on the
TV sc r e e n . The Pa t t e tn Name Tab l e , the P a t t e rn Gene ra tor Tab l e and the S p r i t e
Gene r a t or Tab l e a re u � e d to f o rm t he sp r i t e s . The cont e n t s of t h e s e t ab l e s
mus t a l l b e p rovided b y the micropro ce s s o r . Anima t i on i s ach ieved by a l t e r i ng
t he cont e n t s o f
VRAH
ln
re a l t i me .
4 . 4 0