X25021

2

PIN DESCRIPTIONS

Serial Output (SO)

SO is a push/pull serial data output pin. During a read

cycle, data is shifted out on this pin. Data is clocked out

by the rising edge of the serial clock.

Serial Input (SI)

SI is the serial data input pin. All opcodes, byte ad-

dresses, and data to be written to the memory are input

on this pin. Data is latched by the falling edge of the serial

clock.

Serial Clock (SCK)

The Serial Clock controls the serial bus timing for data

input and output. Opcodes, addresses, or data present

on the SI pin are latched on the falling edge of the clock

input, while data on the SO pin change after the rising

edge of the clock input.

Chip Select (

CS)

When

CS is HIGH, the X25021 is deselected and the SO

output pin is at high impedance and unless an internal

write operation is underway, the X25021 will be in the

standby power mode.

CS LOW enables the X25021,

placing it in the active power mode. It should be noted

that after power-up, a HIGH to LOW transition on

CS is

required prior to the start of any operation.

Write Protect (

WP)

When

WP is LOW, nonvolatile writes to the X25021 are

disabled, but the part otherwise functions normally.

When

WP is held HIGH, all functions, including nonvola-

tile writes operate normally.

WP going LOW while CS is

still LOW will interrupt a write to the X25021. If the

internal write cycle has already been initiated,

WP going

LOW will have no affect on a write.

Hold (

HOLD)

HOLD is used in conjunction with the CS pin to select the

device. Once the part is selected and a serial sequence is

underway,

HOLD may be used to pause the serial

communication with the controller without resetting the

serial sequence. To pause,

HOLD must be brought LOW

while SCK is HIGH. To resume communication,

HOLD is

brought HIGH, again while SCK is HIGH. If the pause

feature is not used,

HOLD should be held HIGH at all

times.

PIN CONFIGURATION

PIN NAMES

Symbol

Description

CS

Chip Select Input

SO

Serial Output

SI

Serial Input

SCK

Serial Clock Input

WP

Write Protect Input

Ground

Supply Voltage

HOLD

Hold Input

6615 PGM T01

6615 FHD F02

CS

SO

WP

VSS

1

2

3

4

8

7

6

5

VCC

HOLD

SCK

SI

DIP/SOIC

X25021