
I
2
C Interface
In I
2
C to I
2
C Mode, the serializer’s control channel inter
-
face sends and receives data through an I
2
C-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 µC
master initiates all data transfers to and from the device
and generates the SCL clock that synchronizes the data
transfer. When an I
2
C transaction starts on the local side
device’s control channel port, the remote side device’s
control channel port becomes an I
2
C master that interfac
-
es with remote side I
2
C peripherals. The I
2
C master must
accept clock-stretching which is imposed by the serializer
(holding SCL low). The SDA and SCL lines operate as
both an input and an open-drain output. Pullup resistors
are required on SDA and SCL. Each transmission con
-
sists of a START condition (
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 (see
). When the mas
-
ter 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
(
). The data on SDA must remain stable while
SCL is high.
Figure 31. START and STOP Conditions
Figure 32. Bit Transfer
SDA
SCL
START
CONDITION
STOP
CONDITION
S
P
SDA
SCL
DATA LINE STABLE;
DATA VALID
CHANGE OF DATA
ALLOWED
MAX9277/MAX9281
3.12Gbps GMSL Serializers for Coax or
STP Output Drive and LVDS Input
www.maximintegrated.com
Maxim Integrated │
37