Atari ST series Technical Reference Manual page 230

Set a Bit on Sound Chip I/O Port
Ongibit()
A t o m i c a l l y s e t s a s in g le b it o f t h e P o r t A I /O r e g i s t e r o n t h e P S G s o u n d
c h ip .
C macro format
i n t b i t n u m ;
O n g i b i t ( b i t n u m ) ;
Machine language format
m o v e . w
m o v e . w
t r a p
a d d q .l
Inputs
b i tn u m
Results
N o n e
See also
O f fg ib it(
222
# b i t n u m , - (s p )
# 3 0 , - ( s p )
# 1 4
# 4 , s p
w o r d
Ongibit
T h e n u m b e r o f th e b it ( 0 - 7 ) to c h a n g e .
Opcode = 30