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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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