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ZiLOG System 8000 Hardware Reference Manual

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HRM
2ilog
HRM
M1
is
used
for
translating
program
memory
references
while
M2
and
M3
translate
all
other
memory
references.
The
selec-
tion
between
M2
and
M3
is
based
on
a
comparison
between
the
logical
address
and
the
contents
of
the
System
Break
Regis-
ter
(SBR),
a
program
addressable
hardware
register.
Logical
addresses
with
values
lower
than
the
SBR
are
treated
as
data
addresses
and
are
directed
to
MMU
M2
(data).
Logical
addresses
that
are
equal
to
or
greater
than
the
SBR,
are
treated
as
stack
addresses
and
are
directed
to
MMU
M3
(stack)
.
A
non-segmented
user
program
runs
in
segment
63;
however,
the
hardware
will
allow
any
segment
between
2
and
63
to
be
used.
As
in
the
nan-segmented
operating
system,
Segment
Descriptor
Register
number
63
in
M1,
M2
and
M3
is
used
to
provide
separate
code,
data,
and
stack
areas,
respectively.
The
only
difference
is
that
the
Normal
Break
Register
(NBR),
also
a
program
addressable
hardware
register,
is
used
to
distinguish
between
code,
data,
and
stack
references
instead
of
the
System
Break
Register.
4.9.2.
MMU
Operation
(Segmented):
A
segmented
operating
system
uses
MMU
M1
(code)
to
provide
an
address
space
con-
sisting
of
up
to
63
segments,
e.g.,
segments
0
to
62.
Seg-
ment
Q3
is
used
to
run
non-segmented
user
programs.
Since
the
attribute
flags
in
the
segment
descriptor
registers
of
MMU
M3
(stack)
are
used
to
configure
different
segments,
no
separation
between
code,
data
or
stack'
references
is
required.
A
segmented
user
program
uses
M2
and
M3
to
provide
an
address
space
consisting
of
124
or
128
segments,
without
separating
code,
data,
and
stack
areas.
If
the
operating
system
is
non-segmented,
then
segment
numbers
0,1
and
64,65
are
reserved
for
the
operating
system
since
it
requires
SDR
number
0
of
M2
and
M3.
In
a
segmented
operating
system,
all
128
segments
are
usable.
4.9.3.
MMU
Configurations:
The
MMU
configuration
is
set
by
hardware
jumpers
on
the
CPU
board
and
by
the
operating
sys-
tem
software.
The
jumpers
are
used
to
configure
the
MMU
select
logic
for
either
a
segmented
or
nonsegmented
operat-
ing
system.
The
operating
system
software
configures
the
System
Configuration
Register
(SCR)
for
running
segmented
or
non
segmented
user
processes
(programs).
Refer
to
Table
4-5
for
possible
jumper
configurations.
4-67
2ilog
4-67

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ZiLOG System 8000 Specifications

General IconGeneral
BrandZiLOG
ModelSystem 8000
CategoryDesktop
LanguageEnglish

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