Note
that
the
98561-66519 processor does
not
have RAM,
I/O,
video circuits,
or
a keyboard
interface.
When
this
processor
is
used in
the
computer,
the
98651-66530
Human
Interface
Card
must
be
used
to
provide interfaces
to
monitors, keyboards,
and
other
peripherals.
An
upgrade
processor kit,
HP
98243A,
is
available for customers
to
upgrade
their
computer
system
from one
with
a MC68010
CPU
to
one
with
the
MC 68020
CPU.
This
upgrade
is
to
be
installed by qualified service personnel.
Central
Processing
Unit
A Motorola MC68020
CPU
functions as
the
main processor chip on this assembly.
It
functions
similar
to
the
MC68010
CPU,
but
has several improvements.
Its
asynchronous
data
bus
is
32-bits wide for
both
addresses
and
internal registers.
The
MC68020
CPU
can
address 4 G-bytes of
RAM
and
can directly address 7.5 M-byte of RAM.
Operating
at
16.6 MHz, it is significantly faster
than
the
MC68010
CPU.
The
CPU
has 57 instruction
types
and
handles 7 major
data
types.
It
also has
18
addressing
modes, 6 maskable
and
1 non-rnaskable
interrupt
levels. Six stack frames exist in
the
MC68020.
Coprocessor
A floating-point coprocessor
is
used
to
increase system performance when
certain
math
routines
are
part
of
the
application. An MC68881 chip performs these functions.
It
implements
the
required
IEEE
standard
capabilities. Performance
is
significantly
greater
than
the
HP
98635A
Floating-Point
Card.
Floating-point
instructions
become
part
of
the
language
of
the
CPU
in its operation.
Memory
Management
Unit
The
MMU provides
the
capability
to
map
any logical page
of
memory into any physical page.
Both
logical
and
physical pages are divided into 4 K-byte pages. A Translation Lookaside Buffer
(TLB)
is
used
to
store
MMU translations.
The
TLB
operates
like a cache
and
is
2K entries deep
split into two 1K
portions
with
one for
the
user
and
one for
the
supervisor.
Cache
Memory
Sub-System
A high-speed direct
mapped
16
K-byte cache memory is external
to
the
CPU
It
stores
both
instructions
and
data
accesses.
It
is set associative
with
a set size of one
and
a line size of two
32-bit words.
Operating
as a
virtual
cache instead
of
a physical cache, it has
greater
performance
than
earlier
HP
Series 200
computer
cache memory sub-systems.
Boot
ROMs
and
Self-Test
LEDs
The
98561-66519 processor
has
a
Boot
ROM whose
operation
is
like
the
98561-66511 processor.
LEDs are used for self-tests
and
their
operation
and
functions
are
the
same.
58
Functional Description
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