LTC1669
U
W U U
APPLICATIONS INFORMATION
Write Word Protocol Used by the LTC1669
1
7
1
1
8
1
8
1
8
1
1
S
Slave Address Wr
A
Command Byte
A
LSData Byte
A
MSData Byte
A
P
1669 TA03
S = Start Condition, Wr = Write Bit = 0, A = Acknowledge, P = Stop Condition
Serial Digital Interface
Write Word Protocol
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
as the LTC1694 SMBus/I2C Accelerator, are required on
these lines.
The master initiates communication with the LTC1669
withaSTARTconditionanda7-bitaddressfollowedbythe
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.
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.
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:
When the master has finished communicating with the
slave, it issues a STOP condition. A STOP condition is
generatedbytransitioningSDAfromlowtohighwhileSCL
is high. The bus is then free for communication with
another SMBus device.
LTC1669
0100 xxx
0100 000
0100 001
0100 010
0100 011
0100 100
0100 101
0100 110
0100 111
LTC-1669-8
0011 xxx
0011 000
0011 001
0011 010
0011 011
0011 100
0011 101
0011 110
0011 111
Acknowledge
AD2
L
AD1
L
AD0
L
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.
L
L
H
L
H
L
L
H
H
H
L
L
H
L
H
H
H
L
H
H
H
1669f
7
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