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APPENDIX
D
SIDES
$OOOD
Diskette Controller Entry Points
~ill
be set to one upon returning to
the
calling
program.
In
addition,
FDSTAT
will
contain
a
number
indicating
the
er,..or
type
($31 -
$39>'
The
error types
are explained in Chapter 28.
If no er,..or
occurs,
then
the
car,..y
bit
of
the
condition code register will
be
set
to
zero
and
FDSTAT
will contain the value
$30.
This byte contains an indication
of
type
of diskette that is in a drive.
the
sign bit (bit
7)
of this location
the
If
is
set
to
one
a~ter
a
diskette has been
accessed,
then
the
diskette
is
single-sided.
If
the
sign bit of this
location is set to zero after a
diskette
has
been
accessed,
then the
diskette is
double-sided.
In
earlier versions of the
diskette
controller
firmware
(EXORdisx
I I )
I
t his 1
0
cat ion UJ ill a
1
UJa
y
s
h
a v e t h e
sign bit set to one.
For
all
of
the firmware
entr~
points described belowl
the content of the registers is unspecified both
upon
e~try
and
exit
from the r.outine.
Each entry point is accessed by
executing a
n
Jump
to
subroutine"
instruction
(~SR).
The
parameters must
have
been set up in RAM as indicated for each
specific function.
It should be noted that the ROM
routines
for
the
diskette
functions run with the interrupt mask bit
set to one in the condition code register.
The routines also
use
the
NMI
vectoT.
Both the NMI vector and the interrupt
mask
are
restored before returning to the calling program.
Name
Address Function
OSLOAD
$E800
This entry point
initializes
the
drive
electTonics
and
loads
the Bootblack and
MDOS
retrieval information block
rrom the
diskette in drive zero.
The Bootblock is
given control after it
has.
been
loaded
from
the
diskette.
Itl
in turn,
causes
the rest of the operating
system
to
be
loaded
into
memory.
No parameters
are
required
for
this
entry
point.
This
function
does
not return control to the
calling
program.
If
an
error
occurs
during
the
Bootblock
load processl
the
error
number
will
be
displa~ed
on
the
sqstem
console and control passed to the
resident debug monitor.
At
ieast
$120
bytes
of memory are
re~uired
starting at
location zero.
If
less
memory
exists,
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