2-20
Theory
of
Operation
HEALER CAM
HEALER RAM
(ADDRESS)
(DATA)
o
31
0
31
32
39
1 a
I
DATA
I
CHECK
1 a
BITS
A
rl"--""
,
1-HEALED
LOCATION
11
•
•
•
•
•
•
1
31
.......
.......
.......
.......
.......
.......
.......
.......
.......
.......
.......
.......
.......
10
11
12
13 14 15
21
22
2930
Y
ADDRESS
X
ADDRESS
CS3
(7
BITS)
(8
BITS)
~
PHYSICAL
MEMORY
ADDRESS
~
~
(19
BITS)
~
X-DON'T
CARE
Figure 2-11. 256K Memory Healing
X
Memory Organization - 512K Byte
RAM
Board
1 1
1
31
J
The 512K
RAM
board
is
similar to the 256K
RAM
finstrate. The board itself
is
a polyimide board
instead of a finstrate. It contains twice as many
RAM
chips
on
the board as the 256K
RAM
finstrate
(Figure 2-12). The
RAM
chips are the same as used on the 256K byte board.
The
Me
on
the
RAM
board develops eight chip select lines, four even
and
four
odd
chip select
lines. Each chip select line selects
one
row of 16K word
RAM
(note that a chip select line in Figure
2-12 goes to every other chip
in
each row. The effect
is
for a
five
chip row instead of ten chips,
and
the chip select goes to either the
odd
numbered chips or the even numbered chips.) Each word
is
still
32
data bits
and
7 check bits,
and
the specific word that
is
addressed
is
selected within the block,
by the X
and
Y address bits.
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