LTC6903/LTC6904

10

69034fa

generated by the slave lets the master know that the latest

byte of information was received. The Acknowledge re-

lated clock pulse is generated by the master. The master

releases the SDA line (HIGH) during the Acknowledge

clock pulse. The slave-receiver must pull down the SDA

line during the Acknowledge clock pulse so that it remains

a stable LOW during the HIGH period of this clock pulse.

Write Word Protocol

The master initiates communication with the LTC6904

with a START condition and a 7-bit address followed by the

Write Bit (Wr) = 0. The LTC6904 acknowledges and the

master delivers the most significant data byte. Again the

LTC6904 acknowledges and the data is latched into the

most significant data byte input register. The master then

delivers the least significant data byte. The LTC6904

acknowledges once more and latches the data into the

least significant data byte input register. Lastly, the master

terminates the communication with a STOP condition.

Slave Address

The LTC6904 can respond to one of two 7-bit addresses.

The first 6 bits (MSBs) have been factory programmed to

001011. The address pin, ADR (Pin 4) is programmed by

the user and determines the LSB of the slave address, as

shown in the table below:

ADR (Pin 4)

LTC6904 Address

0

0010111

1

0010110

TYPICAL APPLICATIO S

Write Word Protocol Used by the LTC6904

Slave Address

A

Wr

MS Data Byte

A

LS Data Byte

A

P

S

71

18

1

8

6903 AI01

11

1

S = Start Condition, Wr = Write Bit = 0, A = Acknowledge, P = Stop Condition

The LTC6904 communicates with a host (master) using

shows the timing relationship of the signals on the bus.

The two bus lines, SDA and SCL, must be high when the

bus is not in use. External pull-up resistors or current

sources, such as the LTC1694 SMBus Accelerator, are

to ensure that the SDA line is released during the ACK

cycle to prevent bus contention.

The LTC6904 is a receive-only (slave) device. The master

can communicate with the LTC6904 using the Write Word

protocols as explained later.

The START and STOP Conditions

When the bus is not in use, both SCL and SDA must be

high. A bus master signals the beginning of a communi-

cation to a slave device by transmitting a START condi-

tion. A START condition is generated by transitioning SDA

from high to low while SCL is high.

When the master has finished communicating with the

slave, it issues a STOP condition. A STOP condition is

generated by transitioning SDA from low to high while

SCL is high. The bus is then free for communication with

another SMBus device.

Acknowledge

The Acknowledge signal is used for handshaking between

the master and the slave. An Acknowledge (active LOW)