Control Data Cyber 170 State Hardware Reference Manual page 184

CP Programming
Executive State
The executive s t a t e uses a combination of hardware, software, and microcode
to
handle t h e following items.
System i n i t i a l i z a t i o n .
Compare/move i n s t r u c t i o n s .
Software e r r o r s and unimplemented i n s t r u c t i o n s t h a t occur i n C Y B E R 170
monitor mode.
a
Processor-detected hardware e r r o r s .
a
Hardware i n t e g r i t y v e r i f i c a t i o n ( d i a g n o s t i c s ) .
I n g e n e r a l , executive s t a t e d e t e r m i n e s , t h e cause of an i n t e r r u p t and decides
whether t o r e t u r n t h e C P t o the i n t e r r u p t e d mode,
t o
h a l t t h e CP, o r t o
simulate a C Y B E R 170 exchange and r e t u r n c o n t r o l t o C Y B E R 170 monitor mode.
Refer t o E r r o r Response i n t h i s chapter.
Floating-point Arithmetic
Format
Floating-point a r i t h m e t i c expresses a number i n t h e form kBn.
k
=
C o e f f i c i e n t
B
=
Base number
n
Exponent o r power t o which t h e base number i s r a i s e d
B i s assumed t o be
2
f o r binary-coded q u a n t i t i e s . I n t h e 60-bit, f l o a t i n g -
point format ( f i g u r e 5-21, the binary point i s considered t o be t o the r i g h t of
t h e c o e f f i c i e n t . The lower
48 b i t s express the i n t e g e r c o e f f i c i e n t , which i s
t h e equivalent of 15 decimal d i g i t s . The s i g n of t h e c o e f f i c i e n t i s separated
from t h e r e s t of the c o e f f i c i e n t and appears i n t h e highest-order b i t
of
the
packed word. Negative numbers a r e represented i n one's complement n o t a t i o n .
The exponent i s biased by complementing the exponent s i g n b i t .