4

FN8206.1

January 3, 2006

Principles of Operation

Serial Interface

SERIAL INTERFACE CONVENTIONS

The device supports a bidirectional bus oriented protocol.

The protocol defines any device that sends data onto the

bus as a transmitter, and the receiving device as the

receiver. The device controlling the transfer is called the

master and the device being controlled is called the slave.

The master always initiates data transfers, and provides the

clock for both transmit and receive operations. Therefore,

the X9520 operates as a slave in all applications.

SERIAL CLOCK AND DATA

Data states on the SDA line can change only while SCL is

LOW. SDA state changes while SCL is HIGH are reserved

for indicating START and STOP conditions. See Figure 1.

On power-up of the X9520, the SDA pin is in the input mode.

SERIAL START CONDITION

All commands are preceded by the START condition, which

is a HIGH to LOW transition of SDA while SCL is HIGH. The

device continuously monitors the SDA and SCL lines for the

START condition and does not respond to any command

until this condition has been met. See Figure 2.

SERIAL STOP CONDITION

All communications must be terminated by a STOP condition,

which is a LOW to HIGH transition of SDA while SCL is HIGH.

The STOP condition is also used to place the device into the

Standby power mode after a read sequence. A STOP

condition can only be issued after the transmitting device has

released the bus. See Figure 2.

18

A1

the use of an external “pull-up” resistor.

19

B2

V1RO V1/Vcc RESET Output. This is an active HIGH, open drain output which becomes active whenever V1/Vcc falls below

the use of an external “pull-up” resistor. The V1RO pin can be forced active (HIGH) using the manual reset (MR) input

pin.

20

A2

V1/Vcc Supply Voltage.

TSSOP

CSP

NAME

FUNCTION

SCL

SDA

Data Stable

Data Change

Data Stable

FIGURE 1. VALID DATA CHANGES ON THE SDA BUS

SCL

SDA

Start

Stop

FIGURE 2. VALID START AND STOP CONDITIONS

X9520