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MAX9273
22-Bit GMSL Serializer with Coax or
STP Cable Drive
27
Maxim Integrated
I2C Interface
In I2C-to-I2C mode, the serializer control-channel inter-
face sends and receives data through an I2C-compatible
2-wire interface. The interface uses a serial-data line
(SDA) and a serial-clock line (SCL) to achieve bidirec-
tional communication between master and slave(s). A FC
master initiates all data transfers to and from the device
and generates the SCL clock that synchronizes the data
transfer. When an I2C transaction starts on the local-side
device’s control-channel port, the remote-side device’s
control-channel port becomes an I2C master that inter-
faces with remote-side I2C peripherals. The I2C master
must accept clock stretching that is imposed by the seri-
alizer (holding SCL low). The SDA and SCL lines operate
as both an input and an open-drain output. Pullup resis-
tors are required on SDA and SCL. Each transmission
consists of a START condition (
Figure 6) sent by a mas-
ter, followed by the device’s 7-bit slave address plus a
R/W bit, a register address byte, one or more data bytes,
and finally a STOP condition.
START and STOP Conditions
Both SCL and SDA remain high when the interface is not
busy. A master signals the beginning of a transmission
with a START (S) condition by transitioning SDA from high
to low while SCL is high (
Figure 24). When the master has
finished communicating with the slave, it issues a STOP
(P) condition by transitioning SDA from low to high while
SCL is high. The bus is then free for another transmission.
Bit Transfer
One data bit is transferred during each clock pulse
SCL is high.
Acknowledge
The acknowledge bit is a clocked 9th bit that the recipient
uses to handshake receipt of each byte of data (
Figure 26).Thus, each byte transferred effectively requires nine bits.
The master generates the 9th clock pulse, and the recipi-
ent pulls down SDA during the acknowledge clock pulse.
The SDA line is stable low during the high period of the
clock pulse. When the master is transmitting to the slave
device, the slave device generates the acknowledge bit
Figure 23. Format Conversion Between GMSL UART and I2C with Register Address (I2CMETHOD = 1)
: MASTER TO SLAVE
SERIALIZER/DESERIALIZER
UART-TO-I2C CONVERSION OF READ PACKET (I2CMETHOD = 1)
UART-TO-I2C CONVERSION OF WRITE PACKET (I2CMETHOD = 1)
F
C
SERIALIZER/DESERIALIZER
F
C
SYNC FRAME
11
DEVICE ID + RD
REGISTER ADDRESS
NUMBER OF BYTES
SYNC FRAME
DEVICE ID + WR
REGISTER ADDRESS
NUMBER OF BYTES
DATA 0DATA NACK FRAME
ACK FRAME
DATA 0DATA N
DATA N
A
DATA 0
WA
DEV ID
S
AP
PERIPHERAL
S
11 18
88
1
17
11
8
11 1
7
DEV ID
RA
AA P
DATA 0DATA N
: SLAVE TO MASTER
S: START
P: STOP
A: ACKNOWLEDGE