M68AW511A datasheet(7/21 Pages) STMICROELECTRONICS

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M68AW511A

OPERATION

The M68AW511A has a Chip Enable power down

feature which invokes an automatic standby mode

whenever Chip Enable is de-asserted (E = High).

An Output Enable (G) signal provides a high

speed tri-state control, allowing fast read/write cy-

cles to be achieved with the common I/O data bus.

Operational modes are determined by device con-

trol inputs W and E as summarized in the Operat-

ing Modes table (Table 2).

Read Mode

The M68AW511A is in the Read mode whenever

Write Enable (W) is High with Output Enable (G)

Low, and Chip Enable (E) is asserted. This pro-

vides access to data from eight of the 4,194,304

locations in the static memory array, specified by

the 19 address inputs. Valid data will be available

at the eight output pins within tAVQV after the last

stable address, providing G is Low and E is Low.

If Chip Enable or Output Enable access times are

not met, data access will be measured from the

limiting parameter (tELQV or tGLQV) rather than the

address. Data out may be indeterminate at tELQX

and tGLQX, but data lines will always be valid at

tAVQV.

Write Mode

The M68AW511A is in the Write mode whenever

the W and E pins are Low. Either the Chip Enable

input (E) or the Write Enable input (W) must be de-

asserted during Address transitions for subse-

quent write cycles. Write begins with the concur-

rence of Chip Enable being active with W low.

Therefore, address setup time is referenced to

Write Enable and Chip Enable as tAVWL and tAVEH

respectively, and is determined by the latter occur-

ring edge.

The Write cycle can be terminated by the earlier

rising edge of E, or W.

if the Output is enabled (E = Low and G = Low),

then W will return the outputs 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 ris-

ing edge of Write Enable, or for tDVEH before the

rising edge of E, whichever occurs first, and re-

main valid for tWHDX or tEHDX.

Table 2. Operating Modes

Note: X = VIH or VIL.

Operation

DQ0-DQ7

Power

Output Disabled

VIL

VIH

Hi-Z

Active (ICC)

Read

VIL

VIH

VIL

Data Output

Active (ICC)

Write

VIL

Data Input

Active (ICC)

Deselect

VIH

Hi-Z

Standby (ISB)

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