Control Data Cyber 170 State Hardware Reference Manual page 56

InputlOutput Unit
Q Register
The 16-bit Q r e g i s t e r holds d a t a f o r s e v e r a l functions such a s t h e address of
t h e operand during d i r e c t addressing and i n d i r e c t addressing, t h e p e r i p h e r a l
address of d a t a used during 1-word c e n t r a l read o r w r i t e i n s t r u c t i o n s , t h e
upper 6 b i t s during constant mode i n s t r u c t i o n s , the channel number on a l l I/O
and channel i n s t r u c t i o n s , t h e s h i f t count, and the r e l a t i v e jump d e s i g n a t o r .
A t d e a d s t a r t , each rank of t h e Q r e g i s t e r i s s e t t o a corresponding PP number
-
Rank 0 i s s e t t o PPO, rank 2 is
s e t t o PP2, and so on.
K
Register
The 7-bit K r e g i s t e r
i s
v i s i b l e t o t h e programmer through t h e maintenance
channel only. This r e g i s t e r holds t h e o p e r a t i o n code f i e l d of
an
i n s t r u c t i o n
f o r d i s p l a y on the
IOU
d e a d s t a r t console and f o r d e a d s t a r t console
i n t e r r o g a t i o n .
When a PP
i s
h a l t e d ( i d l e d ) , t h i s r e g i s t e r c o n t a i n s a l l 1 ' s .
PP Numbering
PPs a r e numbered a s follows:
B a r r e l PPs
1 05 t o
1 1
( o c t a l )
2 20 t o 24 ( o c t a l )
3
25 t o 31 ( o c t a l )
The d e a d s t a r t sequence i s used t o determine PP numbering w i t h i n a b a r r e l . The
sequence a s s i g n s b a r r e l numbers according t o t h e
IOU
b a r r e l r e c o n f i g u r a t i o n
parameter. During t h e f i r s t minor cycle a f t e r d e a d s t a r t , t h e sequence l o a d s a
0
i n t o the Q r e g i s t e r i n b a r r e l 0 .
This d e f i n e s a l l the d a t a i n t h a t rank
of
t h e b a r r e l a s belonging t o PPO, and s i n c e Q i s t h e channel s e l e c t o r , i t a s s i g n s
P P O t o channel 0.
During t h e next minor c y c l e , Q loads with a 1. This d e f i n e s
PP1 and a s s i g n s i t t o channel 1. This process occurs i n p a r a l l e l i n a l l
b a r r e l s u n t i l the I O U a s s i g n s each rank of each b a r r e l with
a
PP number and a
channel number. Reassignment can be done only during a d e a d s t a r t .