®

AS7C251MFT18A

12/24/04, v. 1.2

Alliance Semiconductor

6 of 19

Write enable truth table (per byte)

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

Write all bytes (a, b)

LX

X

X

H

LLL

Write byte a

H

L

L

H

Write byte b

H

L

H

L

Read

HHX

X

HL

H

H

Operation

ZZ

OE

I/O Status

Snooze mode

H

X

High-Z

Read

LL

Dout

LH

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

0 00 11 01 1

0 00 11 0

1 1

0 10 01 11 0

0 11 01 1

0 0

1 01 10 00 1

1 01 10 0

0 1

1 11 00 10 0

1 11 00 1

1 0