Theory
of
Operation
2-23
Memory Organization - 1 Megabyte
RAM
Board
The 1 Megabyte
RAM
board
is
a polyimide board which uses thirty-nine 256K by 1 bit chips. This
allows an organization consisting of 256K words (four bytes per word) which can
be
addressed
without the use of chip select lines, or
"blocks" of
RAM
(Figure 2-13). The word stored
in
the
RAM
is
32
bits
in
length with 7 check
bits.
The
MC
on
the
RAM
board develops eighteen physical address bits from the logical address bits
on
the
MPB,
nine X address bits
and
nine Y address bits. The multiplexed physical addresses are
routed to each chip by the Memory Address Bus. The X address
is
output
first,
with the the Y
address following. Three control lines go to each
RAM
chip: Row Address Select (NRAS) - X
address, Column Address Select (NCAS) -
Y address,
and
Read/Write status (NRW).
MEMORY
ADDRESS
BUS
AND
CONTROL
(9
ADDRESS
AND
3 CONTROL-
NRAS,NCAS,NWR)
12
MPB
32
MC
MEMORY
DATA
BUS
RAM
CHIPS
ARE
256K
X 1
BIT
Figure 2-13. 1 Megabyte Memory Organization
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