Basic
Disk
Operating System (BDOS) Functions
4-2
The
CP/M
-80 BDOS requires an "information address" as input to various func-
tions. This address usually provides buffer
or
File Control Block information used
in the system call.
In
CP/M-86, however, the information address
is
derived from
the current DS register combined with the offset in the
DX
register.
That
is, the
DX
register in
CP/M-86
performs the same function as the
DE
pair
in
CP/M-80,
assuming
that
DS
is
properly set. This poses no particular problem for programs
which use only a single data segment, as
is
the case for programs converted from
CP/M-80. However, when the
data
group
exceeds a single segment, you must
ensure
that
the DS register
is
set to the segment containing the
data
area related
to
the call. Zero values are returned for function calls which are
out
of
range.
BDOS
FUNCTION CODES
Table 4-2 lists the
CP
/M-86 BDOS function calls. The individual BDOS functions
are described in the following three sections
of
this chapter. The function calls are
grouped into simple functions, file operations,
and
memory management
and
program loading functions.
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