NV25256WF

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4

Pin Description

SI: The serial data input pin accepts op−codes, addresses

and data. In SPI modes (0,0) and (1,1) input data is latched

on the rising edge of the SCK clock input.

SO: The serial data output pin is used to transfer data out of

the device. In SPI modes (0,0) and (1,1) data is shifted out

on the falling edge of the SCK clock.

SCK: The serial clock input pin accepts the clock provided

by the host and used for synchronizing communication

between host and NV25256.

CS: The chip select input pin is used to enable/disable the

NV25256. When CS is high, the SO output is tri−stated (high

impedance) and the device is in Standby Mode (unless an

internal write operation is in progress). Every communication

session between host and NV25256 must be preceded by a

high to low transition and concluded with a low to high

transition of the CS input.

WP:

The write protect input pin will allow all write

operations to the device when held high. When WP pin is

tied low and the WPEN bit in the Status Register (refer to

Status Register description, later in this Data Sheet) is set to

“1”, writing to the Status Register is disabled.

HOLD: The HOLD input pin is used to pause transmission

between host and NV25256, without having to retransmit

the entire sequence at a later time. To pause, HOLD must be

taken low and to resume it must be taken back high, with the

SCK input low during both transitions. When not used for

pausing, it is recommended the HOLD input to be tied to

Functional Description

The NV25256 device supports the Serial Peripheral

Interface (SPI) bus protocol, modes (0,0) and (1,1). The

device contains an 8−bit instruction register. The instruction

set and associated op−codes are listed in Table 7.

Reading data stored in the NV25256 is accomplished by

simply providing the READ command and an address.

Writing to the NV25256, in addition to a WRITE command,

address and data, also requires enabling the device for

writing by first setting certain bits in a Status Register, as will

be explained later.

After a high to low transition on the CS input pin, the

NV25256 will accept any one of the six instruction op−codes

listed in Table 7 and will ignore all other possible 8−bit

combinations. The communication protocol follows the

timing from Figure 2.

The NV25256 features an additional Identification Page

(64 bytes) which can be accessed for Read and Write

operations when the IPL bit from the Status Register is set

to “1”. The user can also choose to make the Identification

Page permanent write protected.

Table 7. INSTRUCTION SET

Instruction

Opcode

Operation

WREN

0000 0110

Enable Write Operations

WRDI

0000 0100

Disable Write Operations

RDSR

0000 0101

Read Status Register

WRSR

0000 0001

Write Status Register

READ

0000 0011

Read Data from Memory

WRITE

0000 0010

Write Data to Memory

Figure 2. Synchronous Data Timing

CS

SCK

SI

SO

HI−Z

VALID

IN

VALID

OUT

HI−Z