Control Data Cyber 170 State Hardware Reference Manual page 211

PP Programming
Channel Active/lnactive Flag
A
channel i s normally a c t i v a t e d by a f u n c t i o n ( 7 6 o r 7 7 ) i n s t r u c t i o n o r by
a n
a c t i v a t e channel ( 7 4 ) i n s t r u c t i o n . An e x t e r n a l device can a l s o a c t i v a t e the
channel.
.
A f u n c t i o n i n s t r u c t i o n conditions t h e external. device f o r a coming d a t a o r
s t a t u s information t r a n s f e r .
The i n s t r u c t i o n p l a c e s a 12-bit function word
plus p a r i t y i n the channel r e g i s t e r and s e t s t h e a c t i v e and f u l l f l a g s . The
f u n c t i o n word and a f u n c t i o n s i g n a l a r e s e n t t o t h e e x t e r n a l device. N o a c t i v e
o r f u l l s i g n a l s a r e s e n t during a f u n c t i o n i n s t r u c t i o n . The e x t e r n a l device
a c c e p t s t h e f u n c t i o n word and sends an i n a c t i v e s i g n a l , which c l e a r s t h e
channel a c t i v e and f u l l f l a g s , c l e a r i n g the channel r e g i s t e r .
An a c t i v a t e channel i n s t r u c t i o n prepares a channel f o r d a t a t r a n s f e r and sends
an a c t i v e s i g n a l t o the e x t e r n a l device. Subsequent i n p u t o r output
i n s t r u c t i o n s t r a n s f e r data.
A
disconnect channel (75) i n s t r u c t i o n a f t e r a d a t a
t r a n s f e r r e t u r n s t h e channel t o an i n a c t i v e s t a t e , and an i n a c t i v e s i g n a l i s
s e n t t o the e x t e r n a l device.
Register FulVEmpty Flag
A r e g i s t e r i s f u l l when it contains a f u n c t i o n o r d a t a word f o r an e x t e r n a l
device
o r
c o n t a i n s a ward received from t h e e x t e r n a l device. The r e g i s t e r i s
empty when t h e f l a g c l e a r s . The f l a g i s turned on o r o f f a s t h e r e g i s t e r
changes s t a t e . A channel can only be f u l l when i t i s a c t i v e .
O n d a t a o u t p u t , t h e processor places
a
word i n t h e channel r e g i s t e r ( t h e
channel should be a c t i v e and empty) and s e t s
a
f u l l f l a g .
The d a t a word plus
p a r i t y and a £ 3 1 s i g n a l a r e s e n t t o t h e e x t e r n a l device. The e x t e r n a l device
a c c e p t s the word and sends an empty s i g n a l t o t h e channel, which c l e a r s t h e
,
f u l l f l a g , c l e a r i n g the channel r e g i s t e r . The a c t i v e and empty s t a t u s of the
channel s i g n a l s the PP t o send t h e next word t o t h e r e g i s t e r .
O n d a t a i n p u t , the e x t e r n a l device sends a word and a f u l l s i g n a l t o the d a t a
channel. The word i s placed i n t h e channel r e g i s t e r , and the f u l l f l a g s e t s .
The PP s t o r e s the word and c l e a r s t h e f u l l f l a g , c l e a r i n g t h e d a t a r e g i s t e r .
An
empty s i g n a l i s s e n t t o t h e e x t e r n a l device, s i g n a l i n g i t t o send t h e next
d a t a word.