Spectravideo MKI, Сервисное – Техническое руководство

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Whe n t h e re s e t i n pu t g o e s " h i gh " a l l po r t s w i l l be se t t o the i np u t
mode ( i . e . ,
a
l l 2 4 l i n e s w i l l be i n t he h i gh i mp endance s t a t e ) . Af t e r t he r e s e t i s r emoved
t h e 8 2 5 5A ca n rema i n i n t h e i n p u t mode w i th no a dd i t i ona l i n i t i a l i z a t i on
re q u i re d .
Du r ing t he e x e c u t i on o f the s y s t em p ro g r amme any o f t he o t her m o d e s
ma y b e s e l e c t e d u s i ng
a
s i ng l e ou t p u t i n s t r uc t i o n . Th i s a l l ow s a
s i ng l e 8 2 55A
to s e r v i ce a v a r i e t y of p e r iph e r a l d e v i c e s w i th
a
s im p l e s o f t w a re ma i n t enance
rou t i ne .
The m o d e s f o r P o r t
A and
P o r t
B
c a n b e
se p a ra t e l y
de f i n e d , wh i l e
P
o
r
t
C
i s
d i v ide d i n t o two
por t ions a s
re q u i re d
b y
t he P o r t A a n d P o r t
B
d e f in i t i on s .
A l l o f the ou t p u t reg i s t e r s , i nc l u d i ng
the
s t a t u s f l i p - f l o p s , w i l l b
e re s e t
wh e n e v e r t he mod e i s ch ange d . M o d e s may b e comb i ne d s o t h a t t h e i r f unc t i o na l
d e f i n i t i on c a n be " t a i l o r e d " t o a l mos t any
l / 0
s t r uc t u re . For i n s t ance , G r o
up
B
c a n be p ro g r amme d in M o d e
0
to mo n i t or s im p l e s w i tch c l o s ing s o r d i s p la y
compu t a t i o n a l re s u l t s , G ro u p A cou l d b e p r o g ramm e d in M o d e
1
t o mon i t o r
a
k e y bo a r d o r t a pe r ea d e r on a n i n t e r r u p t- d r iven b a s i s .
The m o d e d e f i n i t i ons and po s s i b l e mode comb i na t i o ns ma y s e em con f u s i ng
at f i rs t
b u t a f t e r a c u r s ory r e v iew o f t he comp l e te d e v i ce ope ra t i on a s imp l e , log
i c a l
I / 0 a p p ro a c h w i l l s u r f ac e . The d e s i g n o f t h e 8 2 5 5A h a s taken
i n t o account
th ing s
s uc h a s e f f i c i e n t P C b o a r d l a y ou t , cont r o l s igna l de f i n i t ion
vs PC
l a y o u t and comp l e t e func t i ona l f l e x i b i l i t y t o supp o r t
a l mo s t any p e r iphera l
d e v i ce w i th no e x t e rn a l l og ic . S uc h d e s ign r e p r e s e n t s t he max imum
use of the
ava i l ab l e
p i
ns
.
B i t S e t / Re s e t Fea t u re
Any
o f
the
e i gh t b i t s
of Por t C can be
S e t o r R e s e t us i ng
a s i ng l e OUTpu t
ins t r uc t i on . Th i s
f e a t u re
re duc e s
s o f twa re re q u i reme n t s
in Con t r o l -based
app l i c a t i o ns .
Whe n P o r t C
i s be i ng u s e d a s s t a t us
/
c on t r o l
for Port
A
or B , the s e b i t s can be
s e t o r res e t by us ing the B i t S e t / R e s e t ope rat i on j us t as if t hey w e re data
ou tput port s .
Con t ro l Func t ions
Whe n the 8 2 5 5A i s p rogrammed to ope rate in mode 1 o r mode 2 , con t r o l s igna l s
a re p rov ided that c a n be used a s i n t e rrupt re que st i npu t s t o t he CPU . The
i n t e r rup t re que s t s i gna l s , genera t e d f rom por t C , can be i nh ib i t e d o r enab l ed
by s e t t ing or rese t t ing the a s s o c i a te d INTE f l ip-f lop , u s ing t he b it s e t / re se t
func t i on of port C .
This func t i o n a l lows the P rog ramme r to d i s a l low or a l l ow a spec i f ic I / O device
to inte rrupt t he CPU w i thout a f f e c t ing any other device in t he int errupt
st rue t u re .
INTE f l i p- f l op de f i n i t i on :
( BI T-SET) - INTE i s SET - Inte rrup t enab le
( B IT- RE SET) - INTE i s RESET - Inte rrupt d i s ab l e
N o t e :
A l l Mas k f l ip-f l op s a r e a u toma t ica l l y re s e t du r ing mode se l ec t ion and
devi ce Re s e t .
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