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SYSTEM DESCRIPTION
SCALL
UCALL
24.9 --
.MDOS
E~uate
File
execute a
branch
to
location
*+2.
The condition codes are changed as in
a
BlTA
instruction;
however,
the
branch
instruction
re~uires
only one
byte of memory.
To be used with a single argument
to
execute a software interrupt (SWI) to
the
MDOS
system
function
handler.
This
macro ensures that the sign bit
of the function byte is set to
zero.
The
symbols ror the system functions
are
defined later in the MDOS
equate
fi Ie.
To
be used with a single argument to
exe~ute
a software interTupt (SWI) to
the
user-defined
function
handler.
This macro ensures that the sign
bit
of
the
Tunction byte is set to one.
The UCALL macro only makes
sense
if
the
user
has
configured
an
SWl
handler.
All other macro definitions in the MOOS equate file
are
for
interna 1 use.
Follo~ing
the macro definitions is a list of names that
identifies all of the system
functions
accessible
via
the
SCALL
macro
(or
an
SWI instruction followed by a function
byte).
These equates are derined using a macro
that
allows
the
labels
to
sequence
themselves.
Thus,
if one label is
removed from the listl the numbers
aSSigned
to
the
labels
will
still
be
consecutive,
ascending integers.
The first
function is given the value
or
zero.
Subsequent
functions
are
assigned a number one higher than the previous function.
If the SCALL
macro
is
used
in
writing
programs,
it
is
suggested
that
the
system symbols ror the system functions
also be used.
After the definitions of the system function symbols
is
a
set
Or
equates
for
all of the ASCII control characters
including space and rub out
characters.
These
symbols
are
followed
by equates ror the special MDOS delimiters used ror
sUTfixes, options,
logical unit numbers,
device
names,
and
family indicators.
Next is a list of MDOS sector equates that defines where
the various system tables
are
located.
In
addition,
the
sector size and the sectors/cylinder,
etc.
I
are defined.
Then;
offsets
into
the
various
system
tables
are
defined.
These equates are followed
by
the
deFinitions
of
the
fie 1 d s i n the I /
a
can t r
0
1 b 1
0
c k (I
ac
B )
1
UI
h i c h ,
i
n t urn
I
Page
24-26
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