I2C
Inter-Integrated Circuit
Invented by: Philips Semiconductors (now NXP
Semiconductors) in 1982.
There are 5 modes of operations for the i2c they are
Standard Mode: 100 kbps
Fast Mode: 400 kbps
Fast Mode Plus: 1 Mbps
High-Speed Mode: 3.4 Mbps
Ultra-Fast Mode: 5 Mbps
I2C (Inter-Integrated Circuit):
The Inter-Integrated Circuit (I2C) Protocol is a
protocol intended to allow multiple "peripheral"
digital integrated circuits ("chips") to communicate
with one or more "controller" chips, used to connect
low-speed devices like sensors, EEPROMs, and
microcontrollers.
It uses only 2 wires:
1. SDA (Serial Data Line): For data transfer.
2. SCL (Serial Clock Line): For synchronization.
3. I2c is a synchronous protocol unlike the
UART .
It supports multi-master and multi-
slave communication.
Packet:
packet Structure:
o Start Bit: Indicates the beginning of
communication.
o Address Frame: 7-bit or 10-bit slave address
+ 1-bit (read/write).
o ACK/NACK: Acknowledgment bit after each
frame
o Data Frame: 8-bit data.
o ACK/NACK: Acknowledgment bit after each
frame.
o Stop Bit: Indicates the end of communication.
Timing diagram :
Keypoints to be taken care of :
1) In the ideal state sda and scl both will be high to
start first sda will be pulled down and followed by
the scl .
2) The data should be same during the positive level of
scl .
3) The data should be changed only at negative level
of scl .
4) Always master will decide the transaction .
5) If r/w bit is 0 then it indicate master writing the data
into the slave
1 indicates the master reading the data from
the slave.
6) Burst length transmission is possible in the i2c .
For stop condition sda will be pulled up to high when the
scl is high.
Differences :
What Are Pull-Up and Pull-Down Resistors?
1) Pull-Up Resistor:
a. A resistor connected between a signal line and
the positive supply voltage (VCC).
b. Ensures the signal line is at a HIGH (1) state
when no active device is driving it.
2) Pull-Down Resistor:
a. A resistor connected between a signal line
and ground (GND).
b. Ensures the signal line is at a LOW (0) state
when no active device is driving it.
3) Typical Value: 4.7 kΩ to 10 kΩ
4) The resistance values should in control if we increase
the resistance will decrease the raising time and
power consumption , increase the noise.
5) The lower resistance will be increase the raising time
and power consumption so need the balanced
resistance.
Advantages :
Simplicity and Low Pin Count:
I2C uses only two wires (SDA for data and SCL for
clock) for communication, regardless of the number of
devices on the bus, simplifying hardware design and
reducing wiring complexity.
Multi-Master, Multi-Slave Architecture:
I2C supports multiple master and slave devices on the
same bus, allowing for flexible and scalable system
designs.
Built-in Addressing:
Each device on the I2C bus has a unique address,
enabling efficient communication and reducing the need
for complex addressing schemes.
Error Handling:
I2C incorporates ACK/NACK (Acknowledge/Not
Acknowledge) functionality, allowing for error detection
and correction during data transmission.
Power Efficiency:
I2C peripherals can be powered down when not in use
without affecting the bus, contributing to overall system
power efficiency.
Disadvantages :
Slower: I2C is generally slower, especially for
high-speed data transfer.
Open-drain design: I2C uses open-drain design,
which limits its speed compared to push-pull
designs used in SPI.
Pull-up resistors: I2C requires pull-up resistors,
which can further limit clock speed and increase
power consumption.
Short distances: I2C is designed for short distances,
and signal integrity can become problematic over
longer distances.
Half-duplex communication: I2C is a half-duplex
communication protocol, meaning data can only
flow in one direction at a time.
