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FUNCTIONAL DESCRIPTIONS
T h i s Tandy KFIT c u s t o m I C c o n s i s t s o f t h e f o l l o w i n g f u n c t i o n a l
b l o c k s :
-
Programmable P e r i p h e r a l I n t e r f a c e ( P P I )
-
Keyboard I n t e r f a c e L o g i c
-
F l o p p y D i s k I n t e r f a c e L o g i c
-
P r o g r a m m a b l e I n t e r r u p t ( e q u i v a l e n t t o I n t e l 8259A)
a n d s h a r i n g i n t e r r u p t l o g i c
-
P r o g r a m m a b l e Timer ( e q u i v a l e n t t o I n t e l 8254-2 a n d
C l o c k D i v i d e r
-
A d d r e s s D e c o d i n g L o g i c
P r o g r a m m a b l e P e r i p h e r a l I n t e r f a c e
T h i s s e c t i o n o f t h e KFIT
c u s t o m
i n t e g r a t e d c i r c u i t
replaces
t h e
I n t e l 8255A t h a t
was
u s e d
on
t h e o r i g i n a l Tandy 1 0 0 0
computer.
On
t h e b l o c k d i a g r a m
f o r
t h i s
s e c t i o n
o f l o g i c , t h e 8255A
i s
r e p r e s e n t e d by t h r e e 74LS244 b u f f e r s a d d r e s s e d by r e a d
A ( 0 0 6 0 ) ,
r e a d B ( 0 0 6 1 ) , r e a d C ( 0 0 6 2 ) . A l s o t h e
t w o
l a t c h e s a d d r e s s e d by
w r i t e
B ( 0 0 6 1 ) ,
w r i t e
C ( 0 0 6 2 ) w h i c h
a r e
p a r t
o f t h e o r i g i n a l
8255A l o g i c .
Keyboard I n t e r f a c e L o g i c
T h i s s e c t i o n of t h e KFIT
c u s t o m
i n t e g r a t e d
c i r c u i t
is d e s i g n t o
s u p p o r t Tandy 1 0 0 0 k e y b o a r d
or
Tandy 1 0 1 e n h a n c e d k e y b o a r d .
KYBDTYP s i g n a l
i s u s e d t o s e l e c t Tandy 1 0 0 0 k e y b o a r d when i s
LOW
or
Tandy 1 0 1 e n h a n c e d k e y b o a r d when
i s
HIGH.
The KYBDTYP
i s
b e i n g
r e a d i n
t o p o r t
FFEB(hex) b i t 7. The KBDDATA
-
k e y b o a r d d a t a
i s
s e r i a l
d a t a b i t
stream
a n d t h e n
is c o n v e r t e d
t o
8 b i t s
p a r a l l e l
d a t a by 74LS322, The
s e r i a l
d a t a
is
e n t e r e d
i n
t h e L O W
t o
H I G H
t r a n s i t i o n
of
t h e KBCLK,
F l o p p y D i s k
Interface
L o g i c
T h i s
s e c t i o n
o f t h e KFIT
c u s t o m
i n t e g r a t e d c i r c u i t
i s
d e s i g n
t o
s u p p o r t
F l o p p y D i s k D i g i t a l
O u t p u t R e g i s t e r
(DOR) f u n c t i o n . T h i s
r e g i s t e r
is
mapped
i n
a d d r e s s 03F2 h e x
-
d a t a b i t 0
t o
7
( w r i t e
o n l y )
t o
g e n e r a t e d r i v e
s e l e c t
DSOB,DSlB,DS2B;
FDCRST (FDC
r e s e t )
DMA/I
a n d MTRONB ( m o t o r ON) s i g n a l . The
DMA/I
s i g n a l
is
u s e d
t o
d i s a b l e FDCINTI, FDCDMRQ, a n d FDACKI s i g n a l s
for
a l l o w i n g t h e
u s e d
of
e x t e r n a l FDC c o n t r o l l e r .
1
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