Cpu Control - Spectravideo SVI 318 Service – Technical Manual

AHD
LOGIC UNIT (ALU)
The 8-b i t a r i t hme t i c. and l o g i c a l in s t r uc t ion of the CPU are execu t e d in the
ALU. Int e rna l l y t he ALU c omm un i c a t e s w i th the reg i s t e rs and t he e x t e rna l d a t a
b u s on t h e i n t e rn a l d a t a bus .
i nc l ude :
Add
Sub t r a c t
Log ic a l AND
Log i c a l OR
Logic a l Exc l u s i ve OR
Compa re
INSTRUCTION REGISTERS
As e a ch i n s t r uc t i o n i s f e t c he d f rom memory , i t i s p l a c e d in the i n s t ruc t i o n
reg i s t e r and d e co de d .
gene rat e s a n d supp l i e s a l l o f t h e cont ro l s i gna l s nec e s s a r
da ta f rom o r t o t h e reg i s t e rs , c on t r o l the ALU and p rovide a l l re q u i re d
e x t e rna l cont r o l s i g na l s .
The t yp e o f func t ions p e r f o rme d by t h e ALU
Le f t or r i ght sh i f t s or rot a t e s
(
a r i thme t i c a nd l og i ca l
Inc rement
Decrement
S e t b i t
Re s e t b i t
Te s t b i t
AN D

CPU CONTROL

T h e c on t r o l s e c t ions p e r f orms t h i s f unc t ion and t he n
4 . 6
)
y
to re a d or wr i t e