Spectravideo MKI, Сервисное – Техническое руководство

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OTHER REG ISTERS
Cu rsor S ta r t Reg ister ( Rl O)
Cu rsor End Reg ister ( R1 1 )
S ta rt Add re ss Reg ister ( H
&
L )
( R1 2 , R 1 3 )
Light Pen Reg i s ter ( H
&
L )
( R1 6 , R1 7 )
Cu rsor Reg i s t e r ( H
&
L )
( R1 4 , R1 5 )
CURSOR
This
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b i t write-on ly reg i ster con t ro l s the
cursor forma t ( see F igure 4-8 ) . B i t 5 is
the b l ink t iming contro l . When bit 5 is
low , the b l ink f requency is 1 / 1 6 of the
ve r t ic a l f ie ld ra te , and when bit 5 is
h igh , the b l i nk f requency is 1 /3 2 of the
ve rtical f ie ld ra t e . Bit _6 is use d to
enab le
�
b l ink . The cu rsor start scan
l ine is se t by the lowe r 5 b i t s .
Th is 5 b i t write-only reg ister se t s the
cu rsor end scan l ine .
S tart Add re s s Register is a 1 4 b i t write­
only reg i s t e r wh ich determ ines the f i rs t
add ress pu t ou t a s a re f resh addres s after
vertical b lank ing . I t consi sts of an
8
bit lowe r reg is te r , and a 6 b i t highe r
reg i s te r .
This 1 4 b i t read-only reg ister is use d to
s tore the contents of the Address Reg i s t e r
( H
&
L ) when the LPSTB input pul ses h igh .
Th is reg i s te r cons i s ts of an 8 b i t lower
and 6 b i t highe r regis t e r .
Th is 1 4 b it read/write reg ister stores the
cursor location . Th is . reg i s te r cons ists of
an 8 b it lower and 6 bit h ighe r registe r .
The Cu rs or S ta rt and End Reg i s te r s a l low a cu rsor o f up to 3 2 scan l ines in
height to be p la ce d on any scan l ines of t he cha racter b lock as shown in Figure
1 0 .
Using B i t s 5 and 6 of the Cursor S tart Regi s te r , the cu rsor is programme d
w.f th b l ink pe r iod s o f 1 6 or 3 2 t imes the f ie ld pe r iod . Opt ional- non-b l ink and
non-di splay modes can a l so be se l ec t e d . When an external 2X b l ink on
cha racte rs is re quire d , it may be neces sary to perform cu rsor b l ink exte rna l ly
as we l l so that both b l i nk ra tes are synchronized. Note tha t an inve r t /non­
inve rt cu rsor is eas i ly imp l emented by p rogramm ing the CRTC for b l ink ing cursor
and exte rna l l y invert ing the vi deo s i gna l with an exc lus ive-OR .
4 . 72