memory
map
The OL contains a Motorola 68008 microprocessor, which can address 1 Megabyte
ot memory,
Ie. from 00000
to
FFFFF Hex. The use ot addresses
Within
this range are
defined
by
Sinclair Research
to
be
as
tollows'
•
FFFFF
coooo
40000
28000
20000
18000
ocooo
00000
RESERVED
RESERVED
RAM
96
Kbytes
RAM
32
Kbyles
I/O
ROM
16
Kbyles
ROM
48
Kbytes
expansion
1/0
addon
RAM
main
RAM
screen
RAM
OLI/O
system
ROM
•
PhYSical
Memory Map
The screen RAM
is
organised
as
a senes
of
sixteen bit words starting
at
address Hex
20000 and progressing
In
the order of the raster scan,
I.e.
from
leK
to
nght with each
display line and then from the top
to
the bottom
of
the picture. The bits
Within
each
word are organised
so
that a pixel
to
the
leK
IS
always more significant than a pixel
to
the right
(i,e,
the
pixel
pattern on the screen looks
the
same
as
the
binary
pattern).
However
the organisation of the colour informaflon
,n
the two screen modes
IS
different:
high
byte
low
byte
mode
AO~O
AO~1
GGGGGGGG
RRRRRRRR
512
mode
(high
res)
GFGFGFGF
RBRBRBRB
256
mode
(low
res)
G-green
B-blue
R-red
F-flash
•
30
Setting the Flash bit toggles the flash
state
and freezes the backgound colour for fhe
flash
to
the value given by
R,
G,
and B for that pixel. Flashing
is
always reset
at
the
beginning of each display
line.
In
high resolution mode, red and green specified together
is
interpreted
by
the hardware
as white,
warning
Use of reserved areas
in
the memory
map
may cause incompatibility
With
tuture Sinclair
products. Spurious output
to
addresses defined
to
be peripheral
I/O
addresses can cause
unpredictable behaviour.
It
is
recommended that these areas are
NOT
wntten
to
and
not used for any other purpose. Poking areas
in
use as Microdnve buffers can corrupt
Microdrive data and can result
in
a loss of Information. Poking areas
in
use such
as
system
tables can cause the system
to
crash and can result
in
the loss of data and
programs,
All
I/O
should be performed using either the relevant Super
BASIC
commands or the
Odos operating system traps,
12/84
•
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