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ZiLOG System 8000 Hardware Reference Manual

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HRM
Zilog
HRM.
A
segmented
user
program
can
run
in
this
configuration,
although
the
Nonsegmented
as,
Segmented
USER
configuration
is
intended
for
that
purpose.
Such
a
user
program
has
a
potential
address
space
of
62
code
and
data
segments.
Nonsegmented
as,
Segmented
USER
This
configuration
is
intended
to
run
exactly
as
the
previ-
ous
configuration,
provided
that
the
CPU
is
in
system
mode
and
the
operating
system
is
running
in
memory
segment
o.
In
addition,
code,
data,
and
stack
references
are
directed
to
M1,
M2,
and
M3
respectively,
and
the
contents
of
the
SBR
are
used
to
select
between
data
and
stack
references.
However,
if
the
CPU
is
in
normal
mode,
MMU
M2
is
enabled
for
segment
numbers
2
to
63,
and
MMU
M3
is
enabled
for
segment
numbers
65
to
127.
If
a memory
reference
is
made,
a
segment
trap
violation
is
generated
and
the
three
MMUs
are
disabled.
Also,
the
suppress
signal
is
generated
by
the
CPU
to
protect
the
system
data
and
stack
areas
from
being
accessed
by
the
user
program.
In
system
mode,
if
the
segment
number
of
a
user
segment
is
generated
(segments
1
to
63,
or
66
to
127),
the
address
translation
is
the
same
as
in
normal
mode.
Separation
of
code,
data,
and
stack
spaces
are
deactivated;
MMU
M2
is
enabled
for
segments
2
to
63;
and
MMU
M3
is
enabled
for
segments
66
to
127.
This
allows
the
operating
system
to
directly
access
any
~ser
segment.
4.9.5.
System
Access
to
User
Space:
To
access
a
user
seg-
ment,
the
operating
system
can
use
a
free
segment
slot
and
set
its
Segment
Descriptor
Register
to
point
at
the
same
memory
area
as
the
target
user
segment's
SDR.
A
nonsegmented
operating
system
running
a non
segmented
user
program
can
directly
access
the
user'
data
and
stack
areas
by
switching
to
system
mode
and
using
the
user
segment
number.
To
access
the
user
code
segment,
one-
of
the
unused
segment
slots
is
set
to
point
at
the
code
segment;
for
example,
number
62.
The
SDRs
for
this
segment
slot
in
M2
and
M3
are
both
set
to
point
at
the
code
segment,
negating
the
contents
of
the
NBR.
A
nonsegmented
operating
system
running
a
segmented
user
program
can
directly
access
any
prot
ion
of
the
user
space
by
switching
directly
into
segmented
mode.
4-69
Zilog
4-69

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ZiLOG System 8000 Specifications

General IconGeneral
BrandZiLOG
ModelSystem 8000
CategoryDesktop
LanguageEnglish

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