Control Data Cyber 170 State Hardware Reference Manual page 58

InputlOutput Unit
The d i s p l a y s t a t i o n c o n t r o l l e r (DSC) i s a t t a c h e d t o CYBER 170 c h a n n e l
lo8.
The D S C i s t h e
I O U
i n t e r f a c e between t h e PPs and t h e s y s t e m c o n s o l e , s e r v i c i n z
b o t h t h e keyboard and t h e cathode-ray t u b e (CRT). It t r a n s m i t s f u n c t i o n words
and d i g i t a l symbol s i z e / p o s i t i o n d a t a t o t h e s y s t e m c o n s o l e , and r e c e i v e s
d i g i t a l c h a r a c t e r codes from t h e keyboard. It a l s o r e c e i v e s d i g i t a l symbol
codes from t h e PPs and c o n v e r t s t h e s e t o a n a l o g s i g n a l s t o t h e CRT.
Real-Time Clock
The r e a l - t i m e c l o c k i s a 1 2 - b i t , f r e e - r u n n i n g c o u n t e r , i n c r e m e n t i n g a t a
1-MHz r a t e .
It
i s permanently a t t a c h e d t o c h a n n e l 148. T h i s c h a n n e l may
be r e a d a t any t i m e b e c a u s e i t s a c t i v e and f u l l f l a g s a r e a l w a y s s e t .
Two-Port Multiplexer
The two-port m u l t i p l e x e r p r o v i d e s communication c a p a b i l i t y between a PP and two
a t t a c h e d t e r m i n a l s .
One p o r t i s r e s e r v e d f o r m a i n t e n a n c e p u r p o s e s , and t h e
o t h e r p o r t i s r e s e r v e d f o r f u t u r e u s e . The two-port m u l t i p l e x e r i s p e r m a n e n t l y
a t t a c h e d t o c h a n n e l 158.
Maintenance Channel
The m a i n t e n a n c e c h a n n e l i s used f o r i n i t i a l i z a t i o n of t h e CP and CM m a i n t e n a n c e
r e g i s t e r s and m o n i t o r i n g o f e r r o r s t a t u s .
The maintenance c h a n n e l c o n s i s t s o f t h e maintenance c h a n n e l i n t e r f a c e on
c h a n n e l 178, a m a i n t e n a n c e a c c e s s c o n t r o l i n e a c h s y s t e m e l e m e n t , and a set
o f i n t e r c o n n e c t i n g c a b l e s .
Central Memory Access
Any PP c a n a c c e s s CM. During a w r i t e from t h e I O U t o CM, t h e I O U a s s e m b l e s
f i v e s u c c e s s i v e 12-bit PP words i n t o a 6 4 - b i t C M word w i t h t h e l e f t m o s t 4 b i t s
u n d e f i n e d , During a CM r e a d , t h e IOU d i s a s s e m b l e s t h e r i g h t m o s t 60 b i t s of t h e
6 4 - b i t C M word i n t o f i v e PP words. To f i n d t h e CM a d d r e s s , a PP r e a d s t h e A
r e g i s t e r . I f b i t 17 o f t h e A r e g i s t e r i s c l e a r , t h e PP u s e s t h e c o n t e n t s o f
t h e A r e g i s t e r f o r t h e C M a d d r e s s . If b i t
17
o f t h e A r e g i s t e r i s s e t , t h e PP
adds t h e r e l o c a t i o n a d d r e s s from t h e R r e g i s t e r t o t h e A r e g i s t e r t o form t h e
CM a d d r e s s .
A
maximum o f 20 PPs i n v a r i o u s s t a g e s o f a s s e m b l y / d i s a s s e m b l y c a n s i m u l t a -
n e o u s l y r e a d CM words, and f i v e PPs c a n w r i t e CM words.