Basic Disk Operating System (BDOS) Functions
where:
dmaad
= current user
DMA
address
dmabase=
current user
DMA
base
curdsk = current user disk, 0-15 (A-P)
usrcode = current user area,
0-15
control_pJlag,
0 means
do
not
echo console
output
to
the printer.
FF
means echo
to
the printer.
DIRECT
BIOS
CALL
ENTRY
RETURN
CL: 32H
FUNCTION
50
AH: Keyboard
Input
Status
DX: BIOS
Descriptor
Offset
DIRECT
BIOS
CALL
or
(no value)
The
Direct BIOS Call function provides a direct BIOS call
and
transfers control
through
the BDOS
to
the BIOS. The
DX
register addresses a five-byte memory area
containing the
BIOS call parameters:
8-bit
16-bit 16-bit
Func
value (CX) value (DX)
]
where
Func
is a BIOS function
number
(see Table 5-1),
and
value (CX)
and
value
(DX)
are the 16-bit values which would normally be passed directly in the
CX
and
DX
registers with the BIOS call.
The
ex
and
DX
values are
loaded
into the 8086
registers before the BIOS call
is
initiated.
NOTE
If
the
eON
IN BIOS subroutine
is
called by this
function, the keyboard input status signal
is
returned in register
AH,
indicating which latch
key
(GRPH1,
GRPH2,
ALT,
etc.)
is
pressed.
(See Appendix E, Keyboard
Input
Status.)
4-31
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