HP 9030 Service Manual page 38

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