Serial communication protocols - what are the differences?

Summary

In this video, the presenter breaks down various embedded communication protocols, explaining their unique features and use cases. Starting with the basics of serial communication, the video covers UART, TTL, RS-232, SPI, and I2C. It highlights the differences in data transmission methods, such as synchronous vs. asynchronous communication, and examines the pros and cons of each protocol. For instance, while SPI offers high-speed, full-duplex communication, I2C is more cost-effective with fewer wires but limited to half-duplex. The video helps viewers understand which protocol suits their needs for different applications.

Takeaways

• 😀 Serial communication sends data one bit at a time on a single line, used widely in embedded systems.
• 😀 A UART (Universal Asynchronous Receiver Transmitter) is a hardware device that transmits and receives data asynchronously without a clock signal, relying on matching baud rates.
• 😀 TTL (Transistor to Transistor Logic) refers to a 5V source used to operate a UART and is not a communication protocol.
• 😀 RS-232 is an active-low communication protocol using voltage levels of -3V to -15V for '1' and 3V to 15V for '0', improving reliability over long transmission lines.
• 😀 RS-232 systems step up and invert the voltage to match the UART's operating range while ensuring signal integrity over long cables.
• 😀 A UART with synchronous communication capability can transmit data more quickly by using an additional clock line, though it's not required.
• 😀 SPI (Serial Peripheral Interface) is a synchronous, full-duplex communication protocol that requires at least four wires: MOSI, MISO, clock, and chip select.
• 😀 SPI's main advantage is its speed and ability to communicate with multiple slave devices, each using its own chip select line.
• 😀 A drawback of SPI is the increasing number of wires (chip select lines) when adding more slave devices, which can make the system more expensive and complex.
• 😀 I²C (Inter-Integrated Circuit) is a synchronous protocol using only two wires (data and clock), simplifying the system, but limiting communication to half-duplex (one-way at a time).
• 😀 I²C allows communication with multiple devices by sending each device's address before data transmission, making it cost-effective but slower than SPI due to half-duplex communication.

Q & A

What does 'serial communication' mean?

Serial communication refers to transmitting data one bit at a time over a single communication line.

What is a UART and how does it function?

A UART (Universal Asynchronous Receiver Transmitter) is a hardware device that allows asynchronous communication, typically using two wires: TX (Transmit) and RX (Receive). It doesn't rely on a clock signal and requires both devices to agree on the baud rate for communication.

What does TTL stand for, and how is it used in embedded communication?

TTL stands for Transistor-to-Transistor Logic, which is a 5V voltage standard used for operating UART communication. It is not a protocol but refers to the voltage levels that are often used in serial communication systems.

How does RS-232 differ from TTL in terms of voltage levels?

RS-232 uses voltage levels between -15V to -3V for logical '1' and +3V to +15V for logical '0', which is more suitable for long-distance communication. In contrast, TTL uses a 5V logic level.

What is the main advantage of using RS-232 over TTL for long-distance communication?

RS-232 is preferred for long-distance communication because its higher voltage levels are more robust against signal degradation over long cables, making it more reliable than TTL for extended distances.

What makes SPI (Serial Peripheral Interface) fast and efficient?

SPI is fast because it is a synchronous protocol, meaning both the master and the slave devices share a clock signal for synchronization. It also supports full-duplex communication, allowing data to flow in both directions simultaneously.

What is the primary drawback of SPI when using multiple devices?

The main drawback of SPI is the need for a dedicated chip select line for each slave device. As the number of devices increases, the wiring complexity and cost also increase, which can be a limiting factor in large systems.

How does I2C differ from SPI in terms of communication lines?

I2C uses only two communication lines: a data line (SDA) and a clock line (SCL), compared to SPI, which requires at least four lines (MISO, MOSI, Clock, Chip Select). This makes I2C a more cost-effective solution for connecting multiple devices.

Why is I2C considered half-duplex, and how does this affect its speed?

I2C is considered half-duplex because it can only transmit data in one direction at a time (either from master to slave or slave to master). This makes it slower than full-duplex protocols like SPI, which can send and receive data simultaneously.

What is the key benefit of I2C’s address-based system?

The key benefit of I2C’s address-based system is that it allows multiple devices to share the same data and clock lines. Each device is uniquely identified by its address, which simplifies wiring and reduces the number of required connections.