I2C

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 • Developed by Philips Semiconductor (NXP) in 1982.

• Serial Communication

INTER- • Half-duplex communication.

INTEGRATED
CIRCUIT • Widely used for short-distance.

• Two Wired Interface.

•Multi-Master / Multi-Slave Configuration.

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CONNECTIONS

- Serial Data (SDA)

- Serial Clock (SCK)

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I2C COMMUNICATION MODES

I2C Mode Speed

Standard Mode 100 kbps
Fast Mode 400 kbps
Fast Mode Plus 1 Mbps
High Speed Mode 3.4 Mbps
Ultra-Fast Mode 5 Mbps

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DATA FORMAT

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START CONDITION
- A start condition always occurs at the start of the transmission and Initiated by
Controller (Master).
- SDA line switches from a high voltage level to a low voltage level.

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 REPEATED START CONDITION
 A start condition can be repeated during a transmission.
 This is a special case, called the repeated start, and is used for changing data transmission
direction.

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ADDRESS FRAME
The address frame contains a 7-bit or 10-bit sequence

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READ/WRITE BIT
A single bit specifying whether the master is sending data to the slave (low voltage level) or requesting data
from it (high voltage level).

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 ACK/NACK BIT
Each frame in a message is followed by an acknowledge/no-acknowledge bit.

If an address frame or data frame was successfully received, an ACK bit is returned to the sender from the receiving
device

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DATA FRAME
After the master detects the ACK bit from the slave, the first data frame is ready to be sent.

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 The data frame is always 8 bits long and sent with the most significant bit first

 Each data frame is immediately followed by an ACK/NACK bit to verify that the
frame has been received successfully.

 The ACK bit must be received by either the master or the slave (depending on who
is sending the data)

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 STOP CONDITION
- After all the data frames have been sent, the master can send a stop condition to the slave to halt the transmission.

- SDA line switches from a low voltage level to a high voltage level.

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I2C DATA
TRANSMISSION
1. The master sends the start condition
to every connected slave by switching
the SDA line from a high voltage level
to a low voltage level before
switching the SCL line from high to
low.

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2. The master sends each
slave the 7or 10-bit
address of the slave it
wants to communicate
with, along with the
read/write bit.

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3. Each slave compares the address
sent from the master to its own
address.
If the address matches, the slave
returns an ACK bit by pulling the SDA
line low for one bit.
If the address from the master does
not match the slave’s own address, the
slave leaves the SDA line high.

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4. The master sends or receives the
data frame.

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5. After each data frame has been
transferred, the receiving device returns
another ACK bit to the sender to
acknowledge successful receipt of the
frame.

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6. To stop the data transmission, the master sends a
stop condition to the slave by switching SCL high
before switching SDA high.

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SINGLE MASTER WITH
MULTIPLE SLAVES
Because I2C uses addressing, multiple slaves
can be controlled from a single master.

With a 7-bit address, 128 (2 ) unique address

are available.

Using 10-bit addresses is uncommon but

provides 1,024 (2 ) unique addresses.

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MULTIPLE MASTERS WITH
MULTIPLE SLAVES
Multiple masters can be connected to a single slave
or multiple slaves.

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ARBITRATION
• Bus arbitration occurs when two or more masters start a transfer at the same time.
• During the transfer, the master constantly monitor the SDA and SCL.
• If the SDA is found high when it was supposed to be low, it assumes that another
main is active and immediately stops its transfer.
• This process is called Arbitration.
•The arbitration mechanism ensures that only one device has control of the bus at any
given time, and that data is transmitted without any errors.

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CLOCK STRETCHING
• An I2C slave is allowed to hold down the clock if it needs to reduce the bus speed.

• A transfer is suspended until the slave releases the SCL line.

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PROS
Only uses two wires.

Supports multiple masters and multiple slaves.

ACK/NACK bit gives confirmation that each frame is transferred successfully.

Widely used protocol.

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CONS
The size of the data frame is limited to 8 bits.

Slower data transfer rate than SPI

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USE CASES
Sensors like TRH, Accelerometers, etc

Displays

Actuators

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SUMMARY
Wires 2
Standard Mode = 100 kbps
Speed Fast Mode = 400 kbps
Fast Mode Plus = 1 mbps
High Speed Mode = 3.4 mbps
Ultra-Fast Mode = 5 mpbs
Synchronous or Asynchronous? Synchronous
Serial or parallel Serial
No. Of Masters Unlimited
No. of Slaves 128 (7 bit) or 1024 (10 bit)

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