7

LTC1669

1669f

Serial Digital Interface

The LTC1669 communicates with a host (master) using

the standard 2-wire interface. The Timing Diagram 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

these lines.

The LTC1669 is a receive-only (slave) device. The master

can communicate with the LTC1669 using the Quick

Command, Send Byte or Write Word protocols as ex-

plained 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 communica-

tion to a slave device by transmitting a START condition.

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)

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 LTC1669

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

Write Bit (Wr) = 0. The LTC1669 acknowledges and the

master delivers the command byte. The LTC1669 ac-

knowledges and latches the command byte into the com-

mand byte input register. The master then delivers the

least significant data byte. Again the LTC1669 acknowl-

edges and the data is latched into the least significant data

byte input register. The master then delivers the most

significant data byte. The LTC1669 acknowledges once

more and latches the data into the most significant data

byte input register. Lastly, the master terminates the

communication with a STOP condition. On the reception

of the STOP condition, the LTC1669 transfers the input

register information to output registers and the DAC

output is updated.

Slave Address (MSOP Package Only)

The LTC1669 can respond to one of eight 7-bit addresses.

The first 4 bits (MSBs) have been factory programmed to

0100. The first 4 bits of the LTC1669-8 have been factory

programmed to 0011. The three address bits, AD2, AD1

and AD0 are programmed by the user and determine the

LSBs of the slave address, as shown in the table below:

LTC1669

LTC-1669-8

AD2

AD1

AD0

0100 xxx

0011 xxx

L

L

L

0100 000

0011 000

L

L

H

0100 001

0011 001

L

H

L

0100 010

0011 010

L

H

H

0100 011

0011 011

H

L

L

0100 100

0011 100

H

L

H

0100 101

0011 101

H

H

L

0100 110

0011 110

H

H

H

0100 111

0011 111

Write Word Protocol Used by the LTC1669

Command Byte

A

Slave Address

A

Wr

LSData Byte

A

MSData Byte

A

P

S

81

71

18

1

8

1669 TA03

11

1

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