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Apple Lisa - Video Display; Memory

Apple Lisa
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Confidential
Lisa
Hardware
Reference
Manual
7-Jul-81
VIDEO
DISPLAY
The
bit
mapped
display
has
360'
dots
vertically
and
720'
dots
horizontail
y
•
It
is
refreshed
from system
~~.
Since
the
video
circuit
cannot
wait
for
a long bus
cycle
to
complete,
the
Memory
Bus
provides
a
direct
path
from system
RAM
to
the
video
refresh
"circuit.
The
CPU
board
synchronizes
CPU
access
to
system
RAM
with
that
of
the
video
circuit.
MEMORY
The
Lisa
memory
management
unit
addresses
16
megabytes of
memory.
Hardware
on
the
CPU
board
divides
this
address
space
into
128
segments, each
with
128 KBytes. This hardware,
called
the
Memory
Management
Unit
(MMU),
takes
a
logical
address
generated
by
the
680'0'0'
and
transforms
it
into
a phYSical
address
indicating
a
poSition
in
RAM
or
I/O.
The
transformation
involves
relocation;
therefore
the
physical
location
of a segment
in
memory
is
unimportant
to a program.
During
the
transformation,
the
MMU
performs
access
checks so
that
the
segment
is
used
only
for
its
intended
purpose.
The
access
checks
help
insure
that
a runaway
process
does
not
destroy
too
much
data
before
being
caught.
There
are
three
physical
address
spaces:
main
memory,
I/O,
and
special
I/O.
The
main
memory
can
contain
up
to
two
megabytes of
RAM.
The
I/O
memory
addresses
all
system
I/O
devices
and
expansion
slots.
The
special
I/O
address
space
is
~eserved
for
the
Boot
ROM
and
MMU
registers.
It
is
used
only
when
starting
the
machine and
when
modifying
the
contents
of
the
MMU
registers.
SYSTEM
MEMORY
MAP
Address
Range
Address Space
Function
-
_
.....
_---.
-----
..
-
..
-
$0'0'0'0'0'0'
- $lFFFFF
Main
Memory
System
Main
Memory
(RAM)
$0'0'0'0'0'0'
-
$QQIFFF
I/O
Slot
0'
Low
Decode
$0'0'20'0'0'
-
$QQ3FFF
I/O
Slot
0'
High Decode
$0'0'40'0'0'
-
$QQ5FFF
I/O
Slot
1
Low
Decode
$0'0'60'0'0'
-
$QQ7FFF
I/O
Slot
1 High Decode
$0'0'80'0'0'
-
$QQ9FFF
I/O
Slot
2
Low
Decode
$QQAOQQ
-
$QQBFFF
I/O
Slot
2
High Decode
$xxOQQQ
- $xx3FFF
Special
I/O Boot
and
self-test
ROM
$~QCOQQ
-
$QQCFFF
I/O Floppy
disk
controller
shared
memory
$QQDOQQ
-
$QQDFFF
I/O
I/O
Board Devices
$OOEQQQ
-
$QQFFFF
I/O
CPU
Board Devices
Page 5

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