Tandy 600 Programmer's Reference Manual page 37

FUNCTION
40h
-
Write
to File
AX
BX
CX
DX
SP:
BP:
SI:
Dl:
IP:
FLG
CS
DS
SS
ES
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Entry:
AH =
40h
(function
code)
BX =
File
handle
CX =
Bytes
to write
DS:DX =
Buffer
address
Exit:
AX
=
status
code
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Function
40h
writes
a block
of
data
to a
file.
On
entry,
BX
contains the
file
handle
of
a
file
opened
with write
access,
CX
contains the
number
of
bytes
to transfer,
and
DX
contains the
offset,
from the
segment
in
DS,
of the buffer containing the
data
to write.
On
return
the carry
flag
will
be
reset
if
no
errors
occurred.
If
the
Carry
flag
is
set,
an
error
occurred
and
the status
code
is in
AX.
Error
Returns:
32