2-20
Theory
of
Operation
Memory Mapping
The Memory Controller has the same memory mapping capability of translating logical addresses
on
the MPB to physical addresses
in
RAM
as the 256K
RAM
Memory Controller. The difference
is
in
the number of mapper
CAM
registers that are used to produce Chip Select signals for row
selection,
and
the use of the most significant Y bit for determining whether the row
is
odd
or
even.
The 256K
RAM
used
16
of the
32
mapper
CAM
registers to produce chip select lines for selecting
rows. The 512K
RAM
uses
all
32
mapper
CAM
registers for selecting 8 rows instead of 4 rows
(Figure
2-10). This
is
accomplished by multiplexing the Chip Select output of the
mapper
CAM,
and
using the most significant bit of the Y address to determine whether the multiplexed output
is
an
odd
numbered row or
an
even numbered row (Figure 2-11). The
RAM
chips
still
do
not use the
most significant bit of the
Y address. It
is
only used by the multiplexer inside the Memory Controller.
MAPPER
CAM
CS
REGISTER
SELECTED
ADDRESS
RON
0
7
1
7
2
7
3
7
4
5
6
6
7
8
9
5
10
11
12
13
4
14
15
16
17
18
3
19
20
21
2
22
23
24
25
1
26
27
28
29
0
30
31
Y
ADDRESS
SELECTED
BLOCK
NUMBER
0
4-K
WORDS
1
4K
WORDS
2
4-K
WORDS
3
4K
WORDS
0
4K
WORDS
1
4K
WORDS
2
4K
WORDS
3
4-K
WORDS
0
4-K
WORDS
1
4-K
WORDS
2
4-K
WORDS
3
4-K
WORDS
0
4-K
WORDS
1
4K
WORDS
2
4K
WORDS
3
4K
WORDS
0
4-K
WORDS
1
4K
WORDS
2
4K
WORDS
3
4-K
WORDS
0
4-K
WORDS
1
4-K
WORDS
2
4-K
WORDS
3
4K
WORDS
0
4K
WORDS
1
4-K
WORDS
2
4-K
WORDS
3
4-K
WORDS
0
4-K
WORDS
1
4K
WORDS
2
4K
WORDS
3
4-K
WORDS
)(
AND
4K
BYTES
4-K
BYTES
4K
BYTES
4K
BYTES
16K
BYTE
RAM
16K
BYTE
RAM
16K
BYTE
RAM
16K
BYTE
RAM
16K
BYTE
RAM
16K
BYTE
RAM
16K
BYTE
RAM
Y
ADDRESS
SELECTS
WORD
WITHIN
THE
BLOCK
4-K
BYTES
4K
BYTES
4-K
BYTES
4K
BYTES
4K
BYTES
4K
BYTES
4-K
BYTES
4K
BYTES
16K
BYTE
16K
BYTE
RAM RAM
16K
BYTE
16K
BYTE
RAM
RAM
16K
BYTE
16K
BYTE
RAM
RAM
16K
BYTE
16K
BYTE
RAM
RAM
16K
BYTE
16K
BYTE
RAM RAM
16K
BYTE
16K
BYTE
RAM
RAM
16K
BYTE
16K
BYTE
RAM
RAM
Figure 2-10. 512K Memory Mapping Organization
4K
BYTES
4-K
BYTES
4K
BYTES
4K
BYTES
16K
BYTE
RAM
16K
BYTE
RAM
16K
BYTE
RAM
16K
BYTE
RAM
16K
BYTE
RAM
16K
BYTE
RAM
16K
BYTE
RAM
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