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Interfaces

Serial Communications (USB, CSI & More)

Serial Communication: An Introduction

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Serial communication involves the sequential transmission of data one bit at a time. It requires two lines: a transmitter line (TX) and receiver (RX) line. All serial communication interfaces are built on the processor’s UART (Universal Asynchronous Receiver/Transmitter) or USART (Universal Synchronous/Asynchronous Receiver/Transmitter) module.

UARTs & USARTs

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UART is a hardware device or microchip that translates data between parallel and serial forms. It is used for asynchronous communication, meaning it doesn't require a clock signal to synchronize the output of bits from the transmitting UART to the sampling of bits by the receiving UART. Instead, the sender and receiver agree on a baud rate (bits per second) before communication begins. UARTs are commonly used in applications like GPS receivers, Bluetooth modules, and wireless radio frequency modules.

USART is similar to UART, but it can also operate synchronously. In synchronous mode, data transfer is synchronized by a clock signal generated by the USART hardware. This allows for higher data rates than asynchronous communication as it eliminates the need for start and stop bits. USARTs are often used in applications that require high-speed wired communication. Both UART and USART require careful configuration of parameters like baud rate, parity, stop bits, and data length. The specific configuration depends on the requirements of the devices being connected.

USB: The Universal Serial Bus

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The Universal Serial Bus (USB) is a wiring and physical connectivity standard for connecting peripherals to computers. It's used for both data transfer and power supply. For example, a digital camera might connect to a computer via a USB interface to transfer photos.

USB ports connect peripheral devices like mice, keyboards, printers, media devices, network adapters, and more. The bus is plug-and-play and hot-swappable, meaning you can connect or disconnect a device without shutting down the computer.

USB comes in various versions, each with different capabilities:

USB 1.0: Released in 1996, it supports a maximum transfer rate of 12 Mbps (Megabits per second) and is largely obsolete today.

USB 2.0: Released in 2000, it supports a high-speed transfer rate of 480 Mbps. It's backward compatible with USB 1.0.

USB 3.0: Released in 2008, it's also known as SuperSpeed USB, and supports a transfer rate of 5 Gbps (Gigabits per second). It's backward compatible with USB 2.0 and USB 1.0.

USB 3.1: Released in 2013, it doubles the transfer rate of USB 3.0 to 10 Gbps.

USB 3.2: Released in 2017, it doubles the transfer rate of USB 3.1 to 20 Gbps.

USB 4.0: Released in 2019, it supports a maximum transfer rate of 40 Gbps and is compatible with Thunderbolt 3.

USB also comes in different connector types:

Type A (most common)

Type B

Mini USB

Micro USB

Type C (reversible and can carry more power for charging).

The maximum recommended length of a standard USB cable (for high speed and above) is 5 meters; beyond this, the signal begins to drop off. For longer distances, active (repeater) cables or hubs can be used.

CSI: The Camera Serial Interface

The Camera Serial Interface (CSI) is a specification of the

Mobile Industry Processor Interface⁠

(MIPI) Alliance. It defines an interface to serve as a bridge between processing units (microprocessors, FPGAs, ASICs) and camera sensors With low power consumption and high bandwidth, CSI ensures real-time image and video processing.

It's the most commonly used camera connection protocol in smartphones and other devices with embedded imaging requirements, such as the Raspberry Pi camera module.

Some of the important technical specifications of the CSI format are as follows:

Physical Interface: CSI typically employs a ribbon type cable and connector for the transmission of data and control signals between the camera and the host processor.

Data Transmission: CSI is a serial interface and therefore, transfers data as a series of data packets.

Data Format: CSI interfaces supports various data formats including RAW Bayer, YUV.

Data Control: Apart from data transfer, CSI also communicates camera control signals for configuring camera parameters and settings.

CSI Versions: There are three commonly used variants of CSI available namely CSI-1, CSI-2, and CSI-3.

Clock Signals: CSI interfaces may include clock signals to synchronize the data transfer between image sensor and processor.

Other Serial Interfaces

R S-485

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RS-485 is a standard for serial communication that is used in industrial control systems. It's often used for long-distance communication. For example, a building automation system might use RS-485 to connect various sensors and actuators throughout a large building.

RS-232

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RS-232 is a standard for serial communication that is used for connecting computers and peripheral devices. It's often used in older or industrial systems-a point of sale system might use an RS-232 interface to connect a cash drawer to a computer. DB-9 connectors are often used for RS-232 serial communication; a vintage computer might use a DB-9 connector to connect to a modem.

Sources:

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https://en.wikipedia.org/wiki/Serial_communication⁠

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https://www.howtogeek.com/811390/how-long-can-a-usb-cable-be/⁠

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https://en.wikipedia.org/wiki/Camera_Serial_Interface⁠

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https://www.supertekmodule.com/csi-cameras-a-comprehensive-guide-to-camera-serial-interface-technology/⁠

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