®

AS7C251MNTD18A

12/23/04, v.2.2

Alliance Semiconductor

P. 6 of 18

Burst order

Key: X = Don’t Care, H = HIGH, L = LOW.

more byte write signals are LOW.

Notes:

1 CONTINUE BURST cycles, whether READ or WRITE, use the same control inputs. The type of cycle performed (READ or WRITE) is chose in the initial

BEGIN BURST cycle. A CONINUE DESELECT cycle can only be entered if a DESELECT CYCLE is executed first.

2 DUMMY READ and WRITE ABORT cycles can be considered NOPs because the device performs no external operation. A WRITE ABORT means a

WRITE command is given, but no operation is performed.

3 OE may be wired LOW to minimize the number of control signal to the SRAM. The device will automatically turn off the output drivers during a WRITE

cycle. OE may be used when the bus turn-on and turn-off times do not meet an application’s requirements.

4 If an INHIBIT CLOCK command occurs during a READ operation, the DQ bus will remain active (Low-Z). If it occurs during a WRITE cycle, the bus will

remain in High-Z. No WRITE operations will be performed during the INHIBIT CLOCK cycle.

5

enables WRITEs to byte “d” (DQd pins).

6 All inputs except

7 Wait states are inserted by setting

8 This device contains circuitry that will ensure that the outputs will be in High-Z during power-up.

9 The device incorporates a 2-bit burst counter. Address wraps to the initial address every fourth BURST CYCLE.

10 The address counter is incremented for all CONTINUE BURST cycles.

11 ZZ pin is always Low in this truth table.

Interleaved burst order (LBO = 1)

Linear burst order (LBO = 0)

A1A0

A1A0

A1A0

A1A0

A1A0

A1A0

A1A0

A1A0

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

0 0

0 1

1 0

CE0 CE1 CE2 ADV/LD R/W

BWn

OE CEN

Address

source

CLK

Operation

DQ

Notes

H

X

X

L

X

X

X

L

NA

L to H

DESELECT Cycle

High-Z

X

X

H

L

X

X

X

L

NA

L to H

DESELECT Cycle

High-Z

X

L

X

L

X

X

X

L

NA

L to H

DESELECT Cycle

High-Z

X

X

X

H

X

X

X

L

NA

L to H

CONTINUE DESELECT Cycle

High-Z

1

L

H

L

L

H

X

L

L

External L to H

READ Cycle (Begin Burst)

Q

X

X

X

H

X

X

L

L

Next

L to H

READ Cycle (Continue Burst)

Q

1,10

L

H

L

L

H

X

H

L

External L to H NOP/DUMMY READ (Begin Burst) High-Z

2

X

X

X

H

X

X

H

L

Next

L to H

DUMMY READ (Continue Burst)

High-Z 1,2,10

L

H

L

L

L

L

X

L

External L to H

WRITE CYCLE (Begin Burst)

D

3

X

X

X

H

X

L

X

L

Next

L to H

WRITE CYCLE (Continue Burst)

D

1,3,10

L

H

L

L

L

H

X

L

External L to H NOP/WRITE ABORT (Begin Burst) High-Z

2,3

X

X

X

H

X

H

X

L

Next

L to H

WRITE ABORT (Continue Burst)

High-Z

1,2,3,

10

X

X

X

X

X

X

X

H

Current L to H

INHIBIT CLOCK

-

4