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AS7C251MPFD32A

AS7C251MPFD36A

Alliance Semiconductor

6 of 19

Write enable truth table (per byte)

Key: X = don’t care, L = low, H = high, n = a, b, c, d;

Asynchronous Truth Table

Notes:

1. X means “Don’t Care”

2. ZZ pin is pulled down internally

3. For write cycles that follows read cycles, the output buffers must be disabled with OE, otherwise data bus contention will occur.

4. Snooze mode means power down state of which stand-by current does not depend on cycle times

5. Deselected means power down state of which stand-by current depends on cycle times

Burst sequence table

Function

GWE

BWE

BWa

BWb

BWc

BWd

Write All Bytes

L

X

X

XXX

H

L

LL

LL

Write Byte a

H

L

L

H

H

H

Write Byte c and d

H

L

H

H

L

L

Read

HH

XX

X

X

H

L

H

HHH

Operation

ZZ

OE

I/O Status

Snooze mode

H

X

High-Z

Read

L

L

Dout

L

H

High-Z

Write

L

X

Din, High-Z

Deselected

L

X

High-Z

Interleaved burst address (LBO = 1)

Linear burst address (LBO = 0)

A1 A0

A1 A0

A1 A0

A1 A0

A1 A0

A1 A0

A1 A0

A1 A0

Starting Address

0 0

0 1

1 0

1 1

Starting Address

0 0

0 1

1 0

1 1

First Increment

0 1

0 0

1 1

1 0

First Increment

0 1

1 0

1 1

0 0

Second Increment

1 0

1 1

0 0

0 1

Second Increment

1 0

1 1

0 0

0 1

Third Increment

1 1

1 0

0 1

0 0

Third Increment

1 1

1 0

0 1

1 0