By replacing complex parallel interfaces with a straightforward yet powerful serial

format to carry data one bit at a time. It performs inter-chip addressing, selection,

control, and data transfer. Speeds are up to 400 kHz (Fast-mode), 1 MHz (Fast-mode

Plus), 3.4 MHz (High Speed-mode), or 5 MHz (Ultra Fast-mode).

copper traces are needed, it enables a smaller PCB, reduces design complexity, and

lowers system cost.

SDA

SCL

uC

New function address

1010011 R/W

New function address

as assigned

New

function

MCU

MCU

RTC

LCD

I/O

A/D

D/A

address pins set high (1) or low (0). Information is transmitted byte by byte, and each byte is acknowledged by the receiver.

There can be multiple devices on the same bus, and more than one IC can act as master. The master role is typically played by a

microcontroller.

Parallel Interface

Master

Write data

Slave

SDA

SCL

transmitter

P

W

S

data

slave address

data

A

A

A

receiver

SDA

SCL

transmitter

receiver

Read data

P

R

S

data

slave address

data

A

A

A

<

n data bytes

>

last data byte

S = Start condition

R/W = read/write

A = Acknowledge

A = Not acknowledge P = Stop condition

The master always sends the clock

< n data >

bytes