Datasheet

DS4420
I
2
C Programmable-Gain Amplifier
for Audio Applications
_____________________________________________________________________ 9
Byte Read: A byte read is an 8-bit information transfer
from the slave to the master plus a 1-bit ACK or NACK
from the master to the slave. The 8 bits of information
that are transferred (most significant bit first) from the
slave to the master are read by the master using the bit
read definition above, and the master transmits an ACK
using the bit write definition to receive additional data
bytes. The master must NACK the last byte read to ter-
minate communication so the slave will return control of
SDA to the master.
Slave Address Byte: Each slave on the I
2
C bus
responds to a slave address byte sent immediately fol-
lowing a start condition. The slave address byte con-
tains the slave address in the most significant 7 bits
and the R/W bit in the least significant bit.
The DS4420’s slave address is determined by the state
of the A0, A1, and A2 address pins as shown in Figure
2. Address pins connected to GND result in a ‘0’ in the
corresponding bit position in the slave address.
Conversely, address pins connected to V
CC
result in a
‘1’ in the corresponding bit positions.
When the R/W bit is 0 (such as in A0h), the master is indi-
cating it will write data to the slave. If R/W is set to a 1,
(A1h in this case), the master is indicating it wants to read
from the slave.
If an incorrect (nonmatching) slave address is written,
the DS4420 will assume the master is communicating
with another I
2
C device and ignore the communication
until the next start condition is sent.
Memory Address: During an I
2
C write operation to the
DS4420, the master must transmit a memory address to
identify the memory location where the slave is to store
the data. The memory address is always the second
byte transmitted during a write operation following the
slave address byte.
I
2
C Communication
Writing a Single Byte to a Slave: The master must gen-
erate a start condition, write the slave address byte (R/W
= 0), write the memory address, write the byte of data,
and generate a stop condition. The master must read the
slave’s acknowledgement during all byte write operations.
Reading a Single Byte from a Slave: Unlike the write
operation that uses the specified memory address byte
to define where the data is to be written, the read oper-
ation occurs at the present value of the memory
address counter. A dummy write cycle can be used to
force the address pointer to a desired location. To do
this, the master generates a start condition, writes the
slave address byte (R/W =0), writes the memory
address where it desires to read, generates a repeated
start condition, writes the slave address byte (R/W = 1),
reads the data byte with a NACK to indicate the end of
the transfer, and generates a stop condition.
See Figure 4 for I
2
C communication examples.
Applications Information
Power-Supply Decoupling
The DS4420 has separate supply voltages for its ana-
log and digital circuitry. For best noise and distortion
performance, place a 0.1µF or 0.01µF capacitor from
V
CC
to GND and from AV
CC
to AGND. These capaci-
tors should be placed as close as possible to the sup-
ply and ground pins of the device.
XXXXXXXX
101 0 A
0
0A
1
A
2
111 1 0001
101 0 A
0
0A
1
A
2
111 1 0001
101 0 A
0
1
A
1
A
2
COMMUNICATIONS KEY
WRITE THE GAIN SETTING F8h
READ THE GAIN SETTING F8h
8-BITS ADDRESS OR DATA
NOTE 2: THE FIRST BYTE SENT AFTER A START CONDITION IS
ALWAYS THE SLAVE ADDRESS FOLLOWED BY THE
READ/WRITE BIT.
START ACK
NOT
ACK
S
S
S
A
A
AA
P
ASr
AN
P
REGISTER SETTING
REGISTER SETTING
A
PN
Sr
STOP
REPEATED
START
NOTE 1: ALL BYTES ARE SENT MOST SIGNIFICANT BIT FIRST.
SHADED BOXES INDICATE THE SLAVE IS
CONTROLLING SDA
WHITE BOXES INDICATE THE MASTER IS
CONTROLLING SDA
Figure 4. I
2
C Communication Examples