HP 9020 User Manual

Theory of Operation 2-17
Each row of memory is logically divided into four blocks of 4K words per block, 32-bits per word
(Figure 2-9). Thus selecting a mapper
CAM register selects a particular block of 4K words. The X
and Y address bits then select a particular word in the block. Because the 256K byte RAM board
has 64K words, only
16 mapper CAM registers are used. As shown in Figure 2-9, the registers that
are used are
0-3,8-11,16-19, and 24-27. The remaining registers (4-7,12-15,20-23, and 28-31)
are not used
and their Map Out bits (bit 0) should be set. The Map Out bit is described in a following
paragraph.
Y ADDRESS
MAPPER CAM CS SELECTED
REGISTER SELECTED BLOCK
ADDRESS
o
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
ROW
3
3
3
3
2
o
NUMBER
o
2
3
o
2
3
o
1
2
3
o
1
2
3
X AND Y ADDRESS SELECTS WORD
WITHIN THE BLOCK
4K WORDS 4K BYTES
4K WORDS 4K BYTES
4K WORDS 4K BYTES
4K WORDS 4K BYTES
4K BYTES 4K BYTES 4K BYTES
4K BYTES 4K BYTES 4K BYTES
4K BYTES 4K BYTES 4K BYTES
4K BYTES _ .. 4_K_B ... Y_T .. E""""Sr_ 4K BYTES
~{I~ ------------~
4K WORDS
4K WORDS 16K BYTE
4K WORDS RAM
4K WORDS
16K BYTE
RAM
16K BYTE
RAM
16K BYTE
RAM
~{I~------------------------~
4K WORDS
4K WORDS 16K BYTE
4K WORDS RAM
4K WORDS
16K BYTE
RAM
16K BYTE
RAM
16K BYTE
RAM
~{I~------------------------~
4K WORDS
4K WORDS 16K BYTE
4K WORDS RAM
4K WORDS
16K BYTE
RAM
16K BYTE
RAM
16K BYTE
RAM
~~{I~--------------------------~
Figure 2-9. 256K Memory Mapping Organization
The 32-bit memory address word on the MPB is shown in Figure 2-10. Bits 0-2 contain the function
code,
and bits 30 and 31 are used for half-word and byte modes, respectively. Bits 3-29 are the 27
bits that specify the logical memory address. The least significant 12 bits of the incoming address are
not mapped. These point to individual locations within the 4K blocks. Eight of the 12 bits
(MPB bits
22-29) comprise the X address. The remaining four bits
(MPB bits 18-21) comprise bits 4-7 of the Y
address. The 15 most significant bits are gated into the MC address mapper.

HP 9020 Specifications

General

Brand	HP
Model	9020
Category	Desktop
Language	English