M68AR024D datasheet(11/19 Pages) STMICROELECTRONICS

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M68AR024D

Write Mode

The M68AR024D, when Chip Select (E2) is High,

is in the Write Mode whenever the W and E1 are

Low. Either the Chip Enable Input (E1) or the Write

Enable input (W) must be de-asserted during Ad-

dress transitions for subsequent write cycles.

When E1 or W is Low, and UB or LB is Low, write

cycle begins on the W or E1 falling edge. When E1

and W are Low, and UB = LB = High, write cycle

begins on the first falling edge of UB or LB. There-

fore, address setup time is referenced to Write En-

able, Chip Enables and UB/LB as tAVWL, tAVEL and

tAVBL respectively, and is determined by the latter

occurring falling edge.

The Write cycle can be terminated by the earlier

rising edge of E1, W, UB and LB.

If the Output is enabled (E1 = Low, E2 = High, G =

Low, LB or UB = Low), then W will return the out-

puts to high impedance within tWLQZ of its falling

edge. Care must be taken to avoid bus contention

in this type of operation. Data input must be valid

for tDVWH before the rising edge of Write Enable,

or for tDVEH before the rising edge of E1 or for tD-

VBH before the rising edge of UB/LB, whichever

occurs first, and remain valid for tWHDX, tEHDX and

tBHDX respectively.

Figure 10. Write Enable Controlled, Write AC Waveforms

AI05991

tAVAV

tWHAX

tDVWH

DATA INPUT

A0-A19

DQ0-DQ15

VALID

tAVWH

tAVEL

tWLWH

tAVWL

tWLQZ

tWHDX

tWHQX

tBLBH

UB, LB

tELWH

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