Atari ST series - Page 187

Rwabs
Read/Write Disk Sectors
Rwabs() Opcode = 4
T his fu nctio n allo w s y o u to re a d o r w rite to th e disk , a se cto r at a tim e.
C macro format
in t m o d e , se cto rs, s ta rt, d riv en u m ;
lo n g bu ffer, sta tu s;
sta tu s = R w a b s(m od e, b uffer, se cto rs , sta rt, d riv en u m );
Machine
m o v e .w
m o v e.w
m o v e.w
m o v e.l
m o v e .w
m o v e.w
tra p
ad d q.l
Inputs
d riv e n um
sta rt
se cto rs
bu ffer
m o d e
language format
# d r iv e n u m , - (sp )
# s ta r t, - (sp )
# s e c to r s , - (sp )
b uffer, - (sp )
# m o d e , - (sp )
# 4 , - (sp )
# 1 3
# 1 4 ,s p
w o rd T h e n u m b er o f th e driv e to us e for th e
re ad o r w rite o p era tio n (0 = d riv e A :,
1 = d riv e B :, an d so o n ),
w o rd T h e startin g se cto r n u m b er for th e tran s
fer
w o rd T h e n u m b e r of se cto rs to be tra n sfe rred
lo n g A p o in te r to th e m e m o ry are a u se d as a
d isk se cto r bu ffer. T his bu ffer sh ou ld
sta rt at an ev e n a d d re ss , a n d sh o u ld h av e
5 1 2 b y te s allo cated to it for ea ch se cto r to
b e re ad o r w ritte n ,
w o rd A flag th at in dica tes w h e th er yo u w ish to
rea d o r w rite secto rs:
0 = R ea d secto rs
1 = W rite secto rs
2 = R ead se cto rs w ith o u t affectin g m e 
d ia ch an ge sta tu s
3 = W rite se cto rs w ith o u t affectin g m e
dia c h a n g e statu s
Results
DO statu s
lo n g A n er r o r c o d e th at in d icate s w h e th er th e tran sfe r w a s
su cce ss fu l. A ze ro sta tu s m e an s n o erro r o ccu rre d .
O th e rw ise , a n eg ativ e G EM D O S e rro r n u m b er is re 
tu rn ed . S ee A p p e n d ix D for a list o f G E M D O S erro r
co d es.
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