Atari ST series Technical Reference Manual page 249

Send Character to Screen
Cconout()
T h is f u n c t i o n s e n d s a s in g le c h a r a c t e r to t h e c o n s o l e s c r e e n d e v i c e .
C macro format
c h a r c h ;
C c o n o u t ( c h ) ;
Machine language format
m o v e . w # c h a r , - ( s p )
m o v e . w # 2 , - ( s p )
tr a p # 1
a d d q .l # 4 , s p
Inputs
c h a r w o r d
Results
N o n e
See also
C c o n o s ( ) , C p m o u t ( ) , C a u x o u t ( )
Cconout
T h e lo w b y t e c o n t a i n s th e A S C I I v a l u e o f
th e c h a r a c t e r to w r i t e to t h e s c r e e n , th e
h i g h b y t e is 0 .
Opcode = 2 ($02)
241