HP 13255 Manual page 15

Memory controller module

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13255

Memory Controller

13255-91252/13

REV

JUN-23-81

3.9.5

MEMRAS is

ANDed with BOARD SELECT the ORed with RFSH RAS to

torm the

row address strobe signal to the memory array (Ul4-11).

CAS is used to

latch data out;

in addition,

CAS is used to determine which module

memory is being addressed.

This is accomplished with a 74LS138, 3 to 8

line decoder.

This decoder uses ADDR18 and ADDR17 at the address pins

(Ul7-2,1)

determine

which

the tour memory modules is being ac-

cessed.

When the

decoder is enabled by

BOARD SELECT,

a CAS at

the

other enable input (U17-5) produces a similar pulse at one

four out-

puts;

this pulse is used as the column address strobe for the accessed

module.

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