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INPUi/QUi?UT FUNCTIONS
25.2 --
D~vice
Dependent
1/0
Functions
the function byte indicates the runction to be
executed
and
can
be
obtained
from
the
MDOS
equate
file.
All system
functions that
perform
input/output
operations
require
a
stac
k
in
the user program area.
The size of the stac
k
must
be at least
80
bl.Jtes (decimal>.
Each
system
function
call
pushes seven bytes on the stack.
Since function calls
ma~
be
nested
~ithin
MDOSI
a large stack is required.
It should
be
no~ed
that
EXbug
does
not
have
sufficient
stack
space
available;
the stack
area
must
be
provided
by
the
user
elseUlhere.
The
device
dependent functions for the console and the
line printer use the device
independent
functions
(section
25.3)
via parameter tables held in the MOOS variable section
of memory.
Any error conditions
detected
by
these
system
runctions
will
cause
the
calling pl'cgT'am to be aborted:
a
standard system
be given to the
these parameter
except
"Buffer
fatal error.
error message to be displayed, and control to
MDOS command interpreter.
Since MDOS manages
tables (reserving,
opening,
etc.), any
error
Overflow"
during
a console input will be a
If}
while accessing the console or the
line
pi'interJ
the
errors
are
to be
handled
b~
the
~alling
program,
the device
irrdependent
I/O
runctio~s
(section
25.3)
must
be
used
instead.
25.
2.
1
Con sol e in put -- .
KEY IN
The
.KEYIN
function
inputs
a
specified
number
or
characters Trom the system console keyboard.
All
characters
entered
(with
the
rollowing exceptions) are stored into"an
input
buffer.
The
function
does
not
return
until
a
terminating carriage return is supplied from the keyboard.
The
following characters are treated as special control
characters when encountered by the
~KEYIN
runction:
Character
Value
RUB OUT
or
DEL
$7F
Function
Removes
entered
last
character
into
buffer
unless
bUTfer is empty.
The removed
character is displayed on the
system
console
to
indicate
that it has been removed
rrom
the burrel'.
No
action occurs
if the .buffer is empty.
\
.j
Page
25-02
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