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IS25C128-3PA3

128K-bit/ 256K-bit SPI SERIAL ELECTRICALLY ERASABLE PROM

Integrated Silicon Solution 

IS25C128

IS25C256

ISSI ®

DEVICE OPERATION

The operations of the IS25C128/256 are controlled by a set of instructions that are clocked-in serially SI pin. (See

Table 3). To begin an instruction, the chip select (CS) should be dropped Low. Subsequently, each Low-to-High

transition of the clock (SK) will latch a stable value on the SI pin. After the 8-bit op-code, it may be appropriate to

continue to input an address or data to SI, or to output data from SO. During data output, values appear on the falling

edge of SK. All bits are transferred with MSB first. Upon the last bit of communication, but prior to any following Low-

to-High transition of SK, CS should be raised High to end the transaction. The device then would enter Standby Mode

if no internal programming were underway.

Table 3. Instruction Set

Name Op-code

Operation

Address

Data(SI)

Data (SO)

WREN 0000 X110

Set Write Enable Latch

-

-

-

WRDI

RDSR

WRSR

READ

WRITE

0000 X100

0000 X101

0000 X001

0000 X011

0000 X010

Reset Write Enable Latch

Read Status Register

Write Status Register

Read Data from Array

Write Data to Array

-

-

-

A15-A0

A15-A0

-

-

D7-D0

-

D7-D0,...

-

D7-D0,...

-

D7-D0,...

-

Notes:

1. X = Don’t care bit. For consistency, it is best to use “0”.

2. Some address bits are don’t care. See Table 5.

3. If the bits clocked-in for an op-code are invalid, SO remains high impedance, and upon CS going High there is no affect. A

valid op-code with an invalid number of bits clocked-in for address or data will cause an attempt to modify the array or

Status Register to be ignored.

WRITE ENABLE (WREN)

When Vcc is initially applied, the device powers up with

both status register and entire array in a write-disabled

state. Upon completion of Write Disable (WRDI), Write

Status Register (WRSR), or Write Data to Array

(WRITE), the device resets the WEN bit in the Status

Register to 0. Prior to any data modification, a WREN

instruction is necessary to set WEN to 1. (See Figure 2

for timing).

WRITE DISABLE (WRDI)

The device can be completely protected from modifica-

tion by resetting WEN to 0 through the WRDI instruc-

tion. (See Figure 3 for timing).

READ STATUS REGISTER (RDSR)

The Read Status instruction tells the user the status of

Write Protect Enable, the Block Protection setting (see

Table 2), the Write Enable state, and the RDY status.

RDSR is the only instruction accepted when a write

cycle is underway. It is recommended that the status of

Write Enable and RDY be checked, especially prior to

an attempted modification of data. The 8 bits of the

Status Register can be repeatedly output on SO after

the initial Op-code. (See Figure 4 for timing).

Integrated Silicon Solution, Inc. — 1-800-379-4774

5

AdvancedInformation Rev. 00E

06/13/06

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