Atari ST series Technical Reference Manual page 202

Get Screen RAM Logical Base Address
Logbase()
T h is f u n c t i o n r e t u r n s t h e b e g i n n i n g a d d r e s s o f lo g ic a l s c r e e n d i s p l a y m e m ­
o r y . T h e lo g ic a l s c r e e n is t h e a r e a in m e m o r y t h a t T O S g r a p h i c s f u n c t i o n s
w r i t e s t o . T h is is u s u a l l y t h e s a m e a r e a a s t h e p h y s i c a l d i s p l a y , b u t c a n b e
c h a n g e d t o u p d a t e a g r a p h i c s d i s p l a y w i t h o u t l e t t i n g t h e u s e r s e e t h e u p ­
d a t e p r o c e s s .
C macro format
l o n g l o g s c r a d d r ;
l o g s c r a d d r = L o g b a s e ( );
Machine language format
m o v e . w # 3 , - (s p )
t r a p # 1 4
a d d q .l # 2 , s p
Inputs
N o n e
Results
DO l o g s c r a d d r l o n g
See also
P h y s b a s e ( ) , S e t s c r e e n ( )
194
Logbase
T h e s t a r t i n g a d d r e s s o f th e lo g ic a l s c r e e n ( t h e
3 2 K m e m o r y a r e a t o w h i c h g r a p h i c s f u n c t i o n s
w r i t e ) .
Opcode = 3