devices
A device
IS
a piece of equipment
on
the OL
to
which data can be sent (input) and from
which data can be output
Since the
system
makes no assumptions about the ultimate
1/0
(input/output) device
which
will
be used, the
1/0
device can be easily changed and the data diverted between
devices.
For
example, a program may have
to
output
to
a printer
at
some point during
ItS
run.
If
the printer
is
not available then the output can be diverted
to
a Microdrive
!lie and stored. The
file
can then be printed
at
a later
date.
1/0
on
the OL can be thought
of
as
being written
to
and read tram a logical file which
is
in
a standard device-
independent form.
All
device
speCitic
operations
are
performed
by
IndiVidual device drivers specially written
for each device
on
the OL. The
system
can automatically tind and include drivers for
peripheral devices which are fitted. These should be written
in
the standard OL device
driver format; see the concept
peripheral expansion
When a device
is
activated a channel
is
opened and linked
to
the device.
To
correctly
open a channel device basic information must sometimes be supplied. This extra
information
is
appended
to
the device
name.
The
file
name should conform
to
the rules
for
a SuperBASIC type name though
it
IS
also possible
to
build up the
file
name (device name)
as
a SuperBASIC stong expression.
tn
summary the general
form
of a
file
name
IS:
identifier [information]
where the complete
file
name (inclUding the extra information) conforms
to
the rules
for
a SuperBASIC
Identifier.
Each logical device
on
the
system
requires
ItS
own particular extra information' although
default parameters
will
be assumed
in
each case where possible:
define
device: = name
•
•
where the form
of
the device name
is
outlined
below.
example for console device
•
Select Console Device
Underscore
Window Width
Separator
Height
Separator - read as
AT
r----
Window X coordinate
/r--------
Separator
Window
Y coordinate
Separator
length of keyboard type
ahead buffer
Console
1/0
I
wXh]
[AxXy]
[k]
default:
example:
- window
Width,
height
- window
X,Y
coordinate
of
upper left-hand corner
- keyboard type ahead buffer length (bytes)
con_
448x180a32x16_128
OPEN
#4,
can
20x5000xO 32
OPEN
#8,
can
-20x50
-
OPEN
#7,con=20x50010x10
•
16
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