Control Data Cyber 170 State Hardware Reference Manual page 231

Two-Port Multiplexer Programming
Output Data
The multiplexer a c c e p t s a maximum d a t a block length of
64
c h a r a c t e r s per
terminal. During t h e block d a t a t r a n s f e r , the m u l t i p l e x e r t e r m i n a t e s t h e
output o p e r a t i o n e i t h e r when it r e c e i v e s an i n a c t i v e s i g n a l from t h e channel or
when t h e output b u f f e r
i s
f u l l .
When t h e output b u f f e r i s f u l l , t h e multi-
p l e x e r sends back an i n a c t i v e s i g n a l i n s t e a d of an empty s i g n a l t o t h e channel
on t h e l a s t output word.
The s i g n a l i n d i c a t e s t h e output b u f f e r a c c e p t s t h e
l a s t output word and i t cannot r e c e i v e anymore d a t a from t h e PP. The multi-
p l e x e r does not allow output t o a f u l l b u f f e r .
The m u l t i p l e x e r sends back a n
i n a c t i v e s i g n a l t o d e a c t i v a t e channel 15 a f t e r t h e m u l t i p l e x e r decodes t h e
previous f u n c t i o n code, which i s
OZXX
(PB w r i t e output b u f f e r ) , and r e c e i v e s a n
a c t i v a t e s i g n a l from t h e PP.
Input Data
The multiplexer does not s t o r e t h e i n p u t d a t a from t h e t e r m i n a l . A l o s t d a t a
c o n d i t i o n e x i s t s i f t h e PP does not i n p u t t h e previous d a t a before t h e new d a t a
a r r i v e s from t h e terminal. The multiplexer allows i n p u t from an empty i n p u t
b u f f e r
.
Request to Send and Data Terminal Ready
The hardware b r i n g s up r e q u e s t t o send and d a t a t e r m i n a l ready a u t o m a t i c a l l y
under t h e following c o n d i t i o n s r e g a r d l e s s of the software RTS and D T R b i t s .
Data i n t h e U A R T output r e g i s t e r .
0
Data i n t h e FIFO output r e g i s t e r .
When no d a t a i s i n t h e FIFO o r UART, t h e software b i t determines RTS and DTR.