Control Data Cyber 170 State Hardware Reference Manual page 233

Maintenance Channel Programming
MCH Function Words
The MCH f u n c t i o n word c o n s i s t s of t h e connect, opcode, and type f i e l d s , which
a r e used a s described I n t h e next t h r e e paragraphs and t a b l e s 5-11 and
5-12.
The connect f i e l d s p e c i f i e s t h e u n i t t o which t h e
MCH i s
connected (CP, CM, or
IOU), c o n t r o l l i n g s e l e c t i o n w i t h i n t h e I O U only.
The u n i t remains c o m e c t e d
u n t i l another connect code s e l e c b s a d i f f e r e n t u n i t . Connect codes 10 t o
178 l e a v e t h e MCB unconnected; i n t h i s s t a t e , t h e i n t e r f a c e can be u s e s f o r
PP t o PP communications.
The OPCODE f i e l d c o n t r o l s t h e u n i t s e l e c t e d by t h e connect code, p r e p a r i n g the
u n i t f o r a coming read/write/echo o p e r a t i o n o r causing t h e u n i t t o h a l t , s t a r t ,
c l e a r , o r d e a d s t a r t .
The use of t h e
TYPE
f i e l d depends on t h e connected u n i t . When t h e C P
i s
t h e
connected u n i t , type codes 1 through 7
s p e c i f y t h e d a t a t y p e i n t h e o p e r a t i o n
t o
be performed.
Also, f o r t h e CP, type code 0 s p e c i f i e s t h a t t h e i n t e r n a l
address of t h e C P r e g i s t e r t o be connected is s p e c i f i e d i n a c o n t r o l word,
which
i s
s e n t
as 2
d a t a words immediately following t h e f u n c t i o n word.
When
IOU i s t h e connected u n i t , type codes 0 through 7 s p e c i f y t h e s t a r t i n g byte
number f o r r e a d l n r i t e operations. The exceptions a r e r e a d i n g t h e o p t i o n s
i n s t a l l e d and element i d e n t i f i e r r e g i s t e r s . CM u s e s A 1 6 t o a c c e s s t h e
maintenance- r e g i s t e r s .