CRTC DESCRIPT ION
( F i gu re S TM- 00 1 - I :
CRTC
B l ock D ia g r am)
The C RTC
cons i s t s of p rogrammab l e hor i zon t a l and ve r t ica l t i m i ng gene ra t o r s ,
p rog ramma b l e l i near add re s s re g i s t e r , p rog rammab l e cursor l o g i c , l ight pen
ca p t u re reg is t e r , and cont ro l c i rc u i t ry for in t e r face to a proc e s s o r bus .
A l l
C RTC
t im ing is der i v e d f rom CLK , us ua l l y the ou tpu t of an e x t e rna l dot rat e
coun t e r . Co i nc idence
( CO )
c i rc u i t s con t inuou s l y compa r e count e r con t e n t s to
the c o n t e n t s o f the p rog rammab l e reg i s t e r f i l e , RO-R1 7 . For ho r i z on t a l t im ing
gene r a t i on , comp a r i sons r e su l t in : ( 1 ) Ho r i z on t a l sync p u l se ( HS ) of a
f re q uency , pos i t i on , and du r a t i on d e t e rm i ne d by the reg i s t e rs .
The Hor i2on t a l coun t e r p roduce s H c l ock wh ich d r ives the Scan L i ne Counter and ,
Ve r t i c a l Con t rol . The conten t s of t he R a s t e r Counter are cont i nuou s ly compared
to t h e Max Scan Line Add re s s Reg i s t e r . A co inc i dence re s e t s the Ra s t e r Counter
and c l ock s t he Ve r t i c a l Coun t e r .
Compa r i s ons o f Ve r t i ca l Coun t e r cont e n t s and Ve r t ica l Reg i s t e r s res u l t in :
( 1 )
Ve r t i c a l s y nc p u l se ( V S ) o f a f re quency and pos i t i on de t e rm ined by the reg i s t e r
- t h e w id th i s f i xe d a t 1 6 ra s t e r l i ne s i n the ve rt ica l con t ro l s e c t i on and i s
n o t p ro g r ammab l e , ( 2 ) Ve r t i c a l D i sp lay o f a f re quency and po s i t i on d e t e rm ined
by the re g i s t e r s .
The Ve r t i c a l Co ntro l Log ic has othe r func t i ons .
( 1 ) Gene ra t e row se l e c t s , RAO-RA4 , f rom t he Ras ter Count for the correspond ing
in t e r lace or non- in t e r lace modes .
( 2 )
Extend the number o f scan l i ne s in the ve rt ica l to t a l by the amount pro
g r amme d in the Ve r t ic a l T o t a l Ad j us t Reg i s te r .
The L inear Add re s s Gene rator i s d r i ven by CLK and loc a t e s the re lat ive
pos i t io n s of cha racte rs in memory w i th the i r po s i t i ons on the s c r een .
Fou rt ee n l i ne s , MAO-MA 1 3 , are ava i l a b l e for addre s s i ng up to fou r page s
of 4K char
a
cte rs
,
8
pa g e s of 2K chara c t e rs , e tc . U s ing the S t a r t Add r e s s
Reg i s t e r , ha rdware scro l l i ng th rough 1 6K cha rac t e r s i s pos s i b l e . The Line a r
A dd re s s Gene ra t or repea t s t h e s ame se quence o f a dd r e s s e s f o r each s can l ine o f
a c ha rac t e r row.
The cu rsor logic determ ines the cursor locat ion , s i z e , and b l ink i ng rat e on the
scre en .
A l l a re prog rammab l e .
The l i gh t pen s t robe g o i ng h igh ca uses the cu rrent . content s o f the Addres s
C o unt e r t o be la tche d in the L i ght P en Reg i s t e r . The con t e n t s of the L i ght Pen
Reg i s t e r are subseque n t l y re a d by the Proce s s or .
I n t e rna l CRTC reg i s t e rs a re p rogrammed by t he p roce s s or th rough the d a ta b us ,
DO-D7 , and the contro l s i gna l s -
R/W,
CS , RS and
E .
4 . 69
Summary of Contents for MKI
Page 1: ...SERVICE TECHNICAL MANUAL VOL 1 l SVI318 328 MKI MKII COMPUTER SYSTEM SVI SPECTRAVIDEO ...
Page 7: ...4 Remove the seven retaining screens 5 Remove the cover 2 2 ...
Page 8: ...6 Remove the screens on the metal cover 7 Remove the metal cover 2 3 ...
Page 9: ...To r e assemble u se the above procedures in the rever se order 2 4 ...
Page 134: ...5 CIRCUIT SCHEMATIC AND COMPONENT LAYOUT 5 1 ...
