Serial Protocols

The purpose of serial communication is to transfer information between devices while using fewer wires than parallel communication.

Synchronous/Asynchronous - Uses a clock signal/Doesn’t use a clock signal.
Half-duplex/Full-duplex - Only one device can send and receive data/Both devices can send and receive data at the same time.
Differential - Instead of using GND and +V which can get corrupted with noise, you use -V and +V with wires usually wrapped around each other, thus canceling out noise.

Other common terms	Name
ADC	Analog to digital converter
DAC	Digital to analog converter
PWM	Pulse width modulation

Protocol Names	Speed	Distance	Communication style	Wires	Sync/Aysnc	Half/Full
UART	Low	Short	Either device can send	2-3	Async	Half
I2C	Low	Short	Master multi-slave	3	Sync	Half
SPI	High	Short	Master multi-slave	4-5	Sync	Full
CAN	Medium	Medium	Network	2	Async	Half
USB	High	Short	Master-slave	4	Sync	Full
EtherCAT	Very high	Medium	Network	8	Sync	Full

UART - Universal Asynchronous Receiver/Transmitter
I2C - Inter Integrated Circuit
SPI - Serial Peripheral Interface
CAN - Controller Area Network
USB - Universal Serial Bus
EtherCAT - Ethernet for Control Automation Technology

UART - Universal Asynchronous Receiver/Transmitter

Simple asynchronous serial communication that sends data one bit at a time(baud rate) over two wires.

Wires	Name
GND	Ground
TX	Transmit
RX	Receive

TX from one device connects to the RX of the other device.

I2C - Inter Integrated Circuit

A two wire serial communication protocol for connecting multiple devices using a shared clock and data line.

Wires	Name
GND	Ground
SDA	Serial data line
SCL	Serial clock line

The master controls the clock and initiates the communication.
Each device requires a 7 or 10 bit address.

SPI - Serial Peripheral Interface

Full duplex synchronous serial protocol where a master communicates with one or more slaves using separate lines for data in, data out, clock, and chip select.

Wires	Name
GND	Ground
CS	Chip select
SCK	Serial clock signal
MOSI	Master out slave in
MISO	Master in slave out

CAN - Controller Area Network

CAN is a network serial protocol, not a master slave one. It is half duplex, asynchronous, differential pairs, and has error correction(CRC).

Wires	Name
CANH	CAN High
CANL	CAN Low

An ID is sent with the data, only the device with the ID processes the data.
- Devices don’t know which device sent the data.
All nodes must agree upon a baud rate.

USB - Universal Serial Bus

USB is a serial protocol that allows devices to connect and exchange info with a host using high speed differential bus.

Wires	Name
VBUS	5v power
GND	Ground
D+	Data positive
D-	Data negative

EtherCAT - Ethernet for Control Automation Technology

EtherCAT is a high performance real time ethernet based serial protocol for industrial automation.

4 twisted pairs of TX and RX wires.