INTRODUCTION
I . I N T R O D U C T I O N
T h e D S - 2 0 2 i s a d u a l c h a n n e l R S - 4 2 2 a s y n c h r o n o u s
s e r i a l c o m m u n i c a t i o n s a d a p t e r f o r s y s t e m s i m p l e m e n t i n g
a n I S A c o m p a t i b l e I / O b u s . D a t a i s c o m m u n i c a t e d
t h r o u g h t w o s h i e l d e d D - 9 c o n n e c t o r s w h i c h p r o v i d e
g r e a t e r s h i e l d i n g f r o m e n v i r o n m e n t a l n o i s e . T h e D S - 3 0 2
is an RS-485 version of the adapter.
The serial interface is implemented with a pair of
1 6 4 5 0 A s y n c h r o n o u s C o m m u n i c a t i o n E l e m e n t s ( A C E s ) . T h e
1 6 4 5 0 i s c o m p a t i b l e w i t h t h e 8 2 5 0 A C E f o u n d i n t h e
o r i g i n a l I B M P C / X T m o d e l s . T h e o p t i o n a l 1 6 5 5 0 A C E
p r o v i d e s a n a d d i t i o n a l F I F O m o d e o f o p e r a t i o n w h i c h
reduces CPU overhead at higher data rates.
The DS-202 / DS-302 allows independent addressing
o f e a c h c h a n n e l t h r o u g h a p a i r o f a d d r e s s d e c o d e
s w i t c h e s ( S W 1 a n d S W 2 ) . T h e s e s w i t c h e s a l l o w e a c h
c h a n n e l t o b e a d d r e s s e d i n t h e I / O a d d r e s s r a n g e 0 0 0 0 H
t h r o u g h 0 7 F F H . E a c h c h a n n e l i s a l s o c a p a b l e o f
s e l e c t i n g a n d / o r s h a r i n g o n e o f s i x p o s s i b l e
interrupt request lines (IRQ 2,3,4,5,6,7).
I I . B O A R D D E S C R I P T I O N
A component diagram of the DS-202 / DS-302 showing
t h e l o c a t i o n s o f t h e 1 6 4 5 0 A C E s , c o n f i g u r a t i o n j u m p e r s ,
a d d r e s s s e l e c t i o n s w i t c h e s , a n d o u t p u t c o n n e c t o r s i s
s h o w n i n f i g u r e 1 . T h e f i r s t c o m m u n i c a t i o n c h a n n e l i s
c o n t r o l l e d b y t h e A C E l a b e l e d U 7 , s w i t c h S W 1 f o r
a d d r e s s i n g , j u m p e r s J 2 a n d J 5 f o r i n t e r r u p t r e q u e s t
selection, jumpers J7 and J8 for output signal control,
a n d i s o u t p u t t h r o u g h c o n n e c t o r C N 1 . T h e s e c o n d
channel is controlled by the ACE labeled U8, switch SW2
for addressing, jumpers J3 and J6 for interrupt request
s e l e c t i o n , j u m p e r s J 8 a n d J 1 0 f o r o u t p u t s i g n a l
control, and is output through connector CN2.
I I I . 1 6 4 5 0 / 1 6 5 5 0 F U N C T I O N A L D E S C R I P T I O N
The 16450 is an improved specification version of
t h e 8 2 5 0 A s y n c h r o n o u s C o m m u n i c a t i o n s E l e m e n t ( A C E )
f o u n d i n t h e o r i g i n a l I B M P C a n d P C / X T s y s t e m s a n d i s
functionally equivalent to the 8250. This ACE performs
s e r i a l - t o - p a r a l l e l c o n v e r s i o n o n r e c e i v e d d a t a a n d
p a r a l l e l - t o - s e r i a l c o n v e r s i o n o n d a t a o u t p u t f r o m t h e
C P U .
iii
Содержание DS-202
Страница 5: ...Figure 1 DS 202 DS 302 component layout ...