Spectravideo SVI 318 Service – Technical Manual page 104

VERT ICAL TIM ING REG ISTE� R'4 , R5 , R6 , R 7 , R8 and R9
The po i n t of re f er e nce f o r ve r t i c a l re g i s t e r s is the top cha r ac t e r pos i t i o n
d i sp l a y e d . Ve r t i c a l reg i s t e r s are p ro g r amme d in cha ra c t e r row t ime s o r scan
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i ne t imes .
Ve r t i c a l To t a l Reg i s t e r ( R4 ) and
Ve r t ic a l T o t a l Adj u s t Reg i s t er
( R5 )
Ve r t i c a l D i sp layed Reg i s t e r
( R6 )
y
Ve r t i c a l S nc Pos i t i on ( R7 )
In t e r l a ce Mode Reg i s t e r ( R8 )
Max imum S c an L i ne A dd re ss
Reg is t e r ( R9 )
The ve r t i ca l f re qu ency of VS is d e t e rm ined
by bo t h R4 and RS .
o f chara c t e r l i ne t ime s i s usua l l y an
i n t e g e r p l u s a f ra c t i on to g e t exac t l y a
50 o r 6 0 ve r t i c a l re f r e sh r a t e .
Hz
i n t e g e r numb e r of cha ra c t e r l ine t imes
m inus o ne is prog rammed in the 7 b i t wr i te­
on l y Ve r t i c a l To ta l Re g i s t e r ; the f rac t io n
i s p ro g ramme d in the 5 b i t wr i te-only
Ve r t i c a l Scan Ad j u s t Reg i s t e r a s a numb e r
o f scan l i ne t i mes .
Th i s 7 b i t wri t e- on l y reg i s t e r dete rm i ne s
t he numb e r o f d i s p l ayed cha ra c te r rows on
the CRT s c r e e n , and is p rog ramme d in
cha r a c te r row t i me s .
Th i s 7 b i t wr i t e - on l y re g i s t e r d e t e rm i ne s
the ve r t i c a l s y nc po s i t i on w i th r e s p ect t o
the re f e rence .
cha r a c t e r row t i mes .
Th i s 2 b i t wr i t e-on l y re g i s t e r con t ro l s the
ra s t e r s c an mode ( s e e F i g u re 4-9 ) .
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b i t and b i t
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and b i t se t , the non- i n t e r l ace r a s t e r
scan mode i s se l ec t e d .
a re ava i l ab l e .
ra s t e r scan mode i s se l ec t e d .
b i t 0 and b i t
and v i d eo ra s t e r scan mo de is se l ec t e d .
Th i s 5 b i t w r i t e - on l y reg i s t e r de t e rm ine s
t he numb e r o f scan l i nes p e r cha rac t e r row
inc l ud ing spa c ing .
i s a max a dd re s s and i s one l e s s t han the
numbe r of scan l i ne s .
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4 .
The c a l c u l a t e d numbe r
I t i s p rog ramme d i n
a re r e s e t , o r b i t 0 is re s e t
Tw o i n t e r l ac e mode s
B o th a re i n t e r l aced sync
A l s o when
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a re s e t , t he i n te r l ace sync
The p ro g ramme d va l ue
The
When