Other Reg Isters - Spectravideo SVI 318 Service – Technical Manual

OTHER REG ISTERS

Cu rsor S ta r t Reg ister ( R l O)
Cu rsor End Reg i ste r ( R1 1 )
S ta rt Add re ss Reg i ste r
( R1 2 , R 1 3 )
Light Pen Reg i s ter
( R1 6 , R1 7 )
Cu rsor Reg i s t e r ( H
( R1 4 , R1 5 )
CURSOR
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
he ight 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 o r 3 2 t imes the f ie ld pe r iod .
non-di s p l a y modes can a l so be se l ec t e d .
cha racte rs is re q u i re 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 synchron i z e d .
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 inve rt ing the vi deo s i gna l with an exc lus ive-OR .
This
ve r t ic a l f ie ld ra te , and when b i t 5 is
ve r t i c a l f ie ld ra t e .
Th is 5 b i t wri t e-on l y reg i s t e r se t s the
&
L )
( H
S tart Add re s s Reg i s t e r is a 1 4 b i t wri t e­
only reg i s t e r wh ich d et erm ines the f i rs t
add re s s pu t ou t a s a re f resh addres s a ft e r
ver t i c a l b lank ing .
b i t lowe r reg is te r , and a 6 b i t highe r
&
( H L )
This 1 4 b i t read-on l y reg is t er is use d to
Th is reg i s te r cons i s ts of an 8 b i t lower
and 6 b i t h i ghe r reg i s t e r .
&
L )
Th is 1 4 b it read/w ri t e reg i s t e r stores the
cursor l ocation .
an 8 b it l ower and 6 b i t h ighe r reg iste r .
4 . 72
b i t wri t e-on l y reg i s t e r con t ro l s the
7
cursor forma t ( see F igure 4-8 ) .
the b l ink t im ing contro l .
low , the b l ink f requency is 1 / 1 6 of the
h igh , the b l i nk f requency is 1 /3 2 of the
�
enab le b l ink . The cu rsor start scan
l ine is se t by the lowe r 5 b i t s .
cu rsor end scan l ine .
reg i s te r .
s to re t he contents of the Address Reg i s t e r
&
( H L ) when the LPSTB input pul se s h igh .
When an external 2X b l ink on
Note tha t an inve r t /non­
B i t 5 is
When bit 5 is
B i t _6 is use d to
I t con s i sts of an
Th is . reg i s te r cons i s t s o f
Opt ional- non-b l ink and
8