Spectravideo MKI, Сервисное – Техническое руководство, Страница: 104 / 134

VERTICAL TIMING REG ISTE� R'4 , R5 , R6 , R7 , R8 and R9
The po i n t of re ference for ve r t ica l reg i s t e r s is the top cha r ac t e r pos i t ion
di sp l a y e d . Ve r t ical reg i s t e r s are p rogramme d in cha ra c t e r row t ime s or scan
1
i ne t imes .
Ve r t ic a l Total Reg i s t e r ( R4 ) and
Ve r t ic a l Total Adj ust Reg i s t er
( R5 )
Ve r t ic a l D i sp layed Reg i s t e r
( R6 )
Ve r t i c a l S
y
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 )
4 .
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The ve r t i ca l f re qu ency of VS is dete rm ined
by bo t h R4 and RS . The c a l c u l a t e d numbe r
o f chara c t e r l ine t ime s is usua l ly an
integer p l u s a f ract i on to get exac t ly a
50 o r 60
Hz
ve r t i c a l re f resh rate . The
integer numb e r of cha ra c t e r l ine t imes
m inus one is prog rammed in the 7 b i t wr i te­
on ly Ve r t ica l Tota l Reg i s t e r ; the f rac t ion
is p rog ramme d in the 5 b i t wr i te-only
Ve r t ica l Scan Ad j ust Reg i s t e r as a numb e r
o f scan l i ne t imes .
Th is
7
b i t wri t e- on l y reg i s t e r dete rmine s
the numbe r of d i s p l ayed cha rac te r rows on
the CRT screen , and is p rog ramme d in
characte r row t i mes .
Th i s
7
b i t wri te-on l y re g i s t e r determine s
the ve r t ic a l sync po s i t i on w i th respect t o
the re ference .
I t i s p rog ramme d in
cha racter row t i mes .
Th is 2 b it wr i t e-on l y reg is t e r con t ro l s the
ras t e r scan mode ( se e Figure 4-9 ) . When
b i t and b i t
1
a re rese t , or b i t 0 is res e t
and b i t
1
se t , the non- i n t e r l ace ras t e r
scan mode i s se l ec t e d . Tw o inter l ac e modes
a re ava i lab l e . Both a re inter laced sync
ra s t e r scan mode i s se l ec t e d . Also when
b i t 0 and b i t
1
a re se t , t he inte r l ace sync
and video ra s t e r scan mode is se l ec t e d .
Th is 5 b i t write-on l y reg i s t e r det e rm ine s
t he numbe r o f scan l i nes per cha rac ter row
inc l ud ing spa c ing . The p rogramme d va l ue
i s a max a dd re ss and i s one l ess than the
numbe r of scan l ine s .