Model 330 Processor Board
Introduction
The
Model 330 processor
board
has
the
following
major
parts:
• 16.17 MHz
MC68020CPU.
• 16.67 MHZ MC68881 Floating-Point Coprocessor.
• 16.67 MHz MC68851 Memory Management Unit
• 6840
Timer.
• Boot ROMs.
•
Self-Test LEDs.
• 4 Mbytes of RAM.
A comparison between
both
processor block diagrams shows
other
differences which
are
the
Paged Mernory Management Unit
and
4 Mbytes
of
RAM. Refer
to
Figure 3-16 for
the
following
descri ptions.
Central
Processing
Unit
An MC68020
CPU
is also used on
the
Model 330 processor board.
It
is
clocked
at
16 MHz.
Memory
Management
Unit
The
Model 330 processor
board
uses
the
MC68851 MMU for its memory management. No cache
is used on
the
Model 330 processor board.
l\1MU connections
to
the
CPU
are
through
the
coprocessor interface. All accesses
to
registers
within
the
PMMU
are done by use
of
coprocessor instructions
rather
than
memory
mapp~
registers.
Page
size is 4 Kbytes
or
larger.
The
TLB
is
a 64-entry CAM containing
the
most
recently used translations. When a miss in
the
TLB
occurs
the
MMU requests
the
bus from
the
MC68020
and
conducts its own
table
walks. When
the
translation
is retrieved
the
bus
is
returned
to
the
MC68020 which re-runs
the
cycle with
the
correct
translation
contained within
the
PMMU.
The
PMMU
can
address
the
8 Mbytes of physical address space
supported
on
l\1odel 330 computers.
For more information on tables within
the
PMMU
consult
the
MC68851 Users Guide.
Functional Description
79
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