Spectravideo MKI, Сервисное – Техническое руководство

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The c u rs o r i s p o s i t i oned by changing the con t e n t s
of
reg i s t e rs
R 1 4 and Rl S .
The c u rs o r can be p l a c e d a t any o f 1 6K charac t e r pos i t ions , thus fac i l i t a t i ng
ha r dware pag ing and scro l l i ng thr ough memory wi t hou t loss o f the cu rso r ' s
orig i n a l pos i t i on .
INTERLACE / NON- INTERLACE DIS PLAY MODES
An i l l u s t ra t i on o f the
3
ra s t e r scan modes of ope ra t ion is hown in Figure 4-1 2
No rma l
s ync
mode i s non- in t e r lace . In th i s mode , each scan l i ne is re f reshed
a t the ve r t i c a l f i e ld ra t e
(
e . g . , 50 o r 60 Hz ) . Frame t ime i s div i d e d into
ev en and odd al t e rna t i ng f i e l d s . The ho r i z on t a l and ve rt i c a l t i ming re l a t i on­
sh i p r e s u l t s in · t he d i s p l aceme nt of scan l ines in t he odd f i e ld w i t h r e spect to
th e
even
f i e l d . Whe n the same in fo rma t ion is pa i n t e d in bo t h f i e l d s , the mode
i s
c a l l e d
" I nt e r lace Sy nc , " t h i s is a use ful mode f or enhanc ing readab i l i t y by
f i l l i ng
in
a cha rac te r . Whe n the even l i ne s o f a charac t e r are d i s p l a y e d i n
t he even f i e ld and t h e o dd l in e s in t he o dd f ie l d , the mode i s c a l l e d
" In t e r l a ce Sync and Video " . Th i s l a s t mode e f f ec t ive ly doub l es the charac t e r
d e n s i t y
on
a
mon i t or of
a
g iven bandw i d t h . T he d i sa dvantage o f both i n te r l ace
modes i s an appa r ent f l icker e ff ec t , wh ich can be re duced by ca re ful mon i t or
de s ign .
The re
a r e
re s t r i c t i ons on the por gramm ing o f CRTC re g i s t e r s for int e r lace
ope r a t i on :
( 1 ) Hor i zont a l t o t a l cha rac t e r count , N ht mus t be odd ( i . e . , an even numbe r
o f cha rac t e r t imes )
( 2 ) For In t e r l ace Sync and V ideo mode on l y , the
max
scan l i ne addres s , N8a
must be odd
(
i . e . , an even number o f scan l ines
)
( 3 )
For I n t e r l ace Sync and V ideo mode on ly , the Ve r t ica l D i sp l a yed Tot a l
cha r ac t e rs must be even .
The p rog ramme d number , Nvd • must be one-ha l f
the ac tua l number re qui re d .
( 4 ) For I n t e r l a ce Sync &
Video
mode
on l y , the
Cu rsor
START and
Cursor End
Reg i s t e rs must bo th be even or bo th odd .
L I GHT PE�
The cont e n t s o f the CRTC Add re s s Counter are s t robed into R 1 6 /R1 7 L ight Pen
Reg i s te r s on the next high to low CLK t rans i t i on a f ter LPSTB goes h igh . In
mo s t syst ems , the l ight pe n signa l wou l d also ca use a p roc e s s o r int errupt
rou t i ne to r ead Rl6 /R1 7 . S low l ight pen re sponse re qu i res t he p roces sor
so f tware to modify the cap ture d add re s s read f rom R1 6 / R1 7 by a ca l ib ra t i on
f a c t o r .
4.
73.