Spectravideo MKI, Сервисное – Техническое руководство, Страница: 72 / 134

THE
VIDEO DISPLAY PROCESSOR TMS-·9918A OR 992.9
TMS-99 18A or 9929
·
vo P gene r a t e s a l l con t ro l , s ynch ro n i z a t ion and compos i t e
v i d eo s i g na l s . I t a l so co n t ro l s the s t ora ges , re t r i eva l and re f re s h o f the
d i sp l a y d a t a s to re d i n t he s c r e e n memo r y .
The VDP u s e s
a 1 0 . 738
MHz c r y s t a l . I t gene r a t e s a l l requ i re d in t e rn a l c l o ck
s i g na l . The CPU C l ock i s s u pp l i e d b y the VDP and i s ob t a i n e d b y
dividing
the
1 0 . 7 3 8
MH z C l ock by
3 .
The r e
a re
t h r ee con t ro l s ig na l s , CSW , CSR and ' MODE ' , f rom t he MPU . The s e
inp u t s a r e us e d to c o n t ro l t h e ope r a t i ng mode o f t h e VDP . C SW
i s
the MPU -
to V DP w r i te se l e c t s ig n a l .
i s the MPU - t o - VDP r e a d se l e c t s ig na l .
' MOD E ' i s t h e s i gna l wh i c h d e t e rm in e s the s o u r c e or de s t i na t ion o f a rea d
or
wr i te
da ta
t ra ns f e-r re d t o t he d i s p la y memory RAM .
V id eo Mod e s
The V DP
d i sp lays
an image on t h e s c r e e n tha t can be s t
be env i s ione d as a s e t of
d i sp la y
p lanes
s andw i ched toge t he r . F i gu re 4-4 show s t he de f i n i t i on of
each of
t h e p l a n e s . Obj ec t s o n p l an e s c l o s e s t to t h e v i e wer have h ighe r
p
r
i
o
r i
t y
.
I n
c a s e whe re t w o e n t i t i e s o n t w o
d i
f f e
r
e
nt p l anes a re occupy ing t he s ame
s po t o n
t h e sc r e e n , t h e e n t i t y o n t h e h ighe r
p r i o r i t y p l ane w i l l show at
tha t p o i n t .
F o r an e n t i t y on a spec i f ic
p la n e
t o show t h roug h , a l l p l an e s
i n f r ont of that
p l ane mus t be t r an s p a r e n t at tha t p o i n t . The f i r s t
32
p l ane s ( F i g u re 4-5 ) each
may c on t a i n
a s in
g l e s p r i t e .
( S p r i te a re
p a t te rn ob j e c t s whose po s i t i ons
on
the sc r e e n are de f i ne d b y ho r i z ont a l and ve r t i c a l coo r d i na t e s in VRAM . ) The
a r e a s of t he S p r i te P l ane s ,
ou t s ide of
t he
sp r i te i
t s
e l f , a re t ransparent .
S ince t h e c o o r d i na t e s o f t h e
s p r i t e are
i n te rms of p i xe l s , the
sp r i t e can be
p o s i t i o ne d and move d about v e r y a c cu ra t e l y . S p r i te s a re
ava i l ab l e in t h ree
s i z e s :
8 x 8
p i xe l s , 16
x
1 6
p i xe l s , and 32
x
32 p i xe l s . Beh ind the S p r i t e
P l a ne i s t he P a t t e rn P l a ne . The P a t t e rn P l a ne
i s use d for t e x t u a l a n d g raph ics
ima g e s g e n e ra t e d
by
the Text , Grap h i c s
I, Graph i c s
I I ,
or Mul t i c o l ou r mode s .
Beh i n d t he P a t t e rn P l ane i s
the backd rop , wh ich i s l a rger i n a rea t han the
o t he r p l a n e s so t h a t i t form s a
bo rder aroun d the other p la ne s . The
l a s t
and
l owe s t
p r i o r i ty
p la ne
is t he Ex t e rnal V ideo P l ane . I ts i mage is de f ined by the
e
x
te r
n
a
l v i d eo i npu t p i n .
The backdrop cons i s t s of a s in g l e co l ou r use d for
t he
d i sp lay bord e r s and as t he de fau l t co l ou r f o r t he a c t ive d i s p l ay a rea . The
d e f a u l t
co l ou r
is s t o re d in
the VDP reg i s t e r 7 . Whe n the backdrop co l o u r
reg i s t er
con t a i ns t he t r an spare nt cod e , t he back d r op au toma t i ca l ly de f au l t s to
b l a ck i f
the e x t e rn a l vi d eo mode is no t s e l ec t e d .
4 . 39