Embedded video camera interface

August 23, 2023

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There are various video interfaces, including input and output. In this issue, we will summarize the commonly used camera interfaces. The use of analog cameras on the arm generally needs to be converted into digital signal acquisition through the interface. Only digital cameras are considered here. Generally speaking, it is divided into two categories: parallel port, serial port and USB port.

1.USB interface

One of the most common and widely used CMOS image interfaces, also known as UVC interfaces. The most compatible. Linux systems support the best. Use the USB drive-free UVC protocol to access at any time. It is also normal to use this kind of interface to pull a 5-meter cable. Generally use a 720P or 1080P camera. Because the video streaming rate is far below the transfer rate of USB2.0, there is no need to consider the issue of USB2.0 or 3.0.

2. MIPI-CSI interface

The MIPI-CSI (MIPI Camera Serial Interface) interface is a dedicated interface for cameras and image sensors, capable of high-speed, high-resolution image transmission. Data transmission is performed in the form of differential signals, which can support multiple differential signal lines, such as 2 or 4 differential signal lines, to meet different bandwidth requirements. Each differential signal line is used to transmit a specific data channel, such as pixel data, clock signal, control signal and so on. An upgraded MIPI CSI-2 is now also introduced.

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3. DVP interface

DVP (Digital Video Port) interface is a digital video interface standard used to transmit image and video data. The DVP interface uses a parallel transmission method, that is, each data bit is transmitted using a signal line. Common DVP interfaces include 8-bit DVP and 16-bit DVP, where 8-bit DVP uses 8 signal lines for data transmission and uses the BT656 protocol, while 16-bit DVP uses 16 signal lines and uses the BT1120 protocol.

Clock signal: DVP interface uses a clock signal (Pixel Clock) to synchronize data transmission. The clock signal determines the sampling moment of each pixel data, so that the receiving end can accurately restore the image.
Data channel: DVP interface supports multiple data channels, usually including pixel data channel and synchronous signal channel. The pixel data channel is used to transmit the pixel value of the image, and the synchronization signal channel is used to transmit the line synchronization signal and the field synchronization signal to help the receiving end determine the beginning and end of each line and each frame. There are also two ways of internal synchronization and external synchronization. Internal synchronization and data contain synchronous signals, and external synchronization has separate line synchronization and field synchronization.
Data format: DVP interface can support different data formats, such as RGB, YUV, etc. The specific data format depends on the support capabilities of the connected image sensor and image processor.
Transmission rate: The transmission rate of the DVP interface is limited by the clock frequency and data bit width. Higher clock frequency and data bit width can achieve higher data transfer rate, thus supporting higher image resolution and frame rate.
This interface can also collect video data of the CIF protocol. I have always been confused here, whether to use CIF as an interface or a protocol. But I think CIF is an agreement in essence.