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Interfacing Processors to Audio and Video Devices


Connecting to video sources
Figure 8 shows how a CMOS imager can connect to an embedded processor. Here, the TWI control channel connects to a Micron CMOS image sensor's I²C bus for device configuration, while the image data flows straight into the Blackfin 8-bit PPI (which could be configured for 10, 12 or even 16 bits, depending on the resolution of the sensor).


8. CMOS imager connection to Blackfin processor

While Blackfin's PPI is, in the generic sense, a high speed parallel port with a straightforward interface (16 data lines, up to three frame syncs, and a clock), the port does incorporate some video-friendly features that work hand in hand with the processor's DMA engine. The details of the PPI are too numerous to articulate in this article, but they are readily available on the Analog Devices website.

The imager in this example provides the pixel clock as well as video framing: Horizontal sync demarcates the valid line region and the Vsync serves as a "frame valid" signal. Other sensors support the ITU-R BT.656 standard, in which case these synchronization signals are not needed. The Blackfin EZ-Extender cards and EZ-KITs support connection to a wide range of CMOS sensors from leading vendors including Micron, Omnivision, and Kodak, as illustrated in Figure 9.


9. Micron camera board connected to Blackfin EZ-KIT
If a video-in application comes from an analog source—an analog camcorder, for example—the signal must first pass through a video decoder. In the example of Figure 10, the processor configures the decoder via I²C and the TWI interface, and its PPI receives an 8-bit digital data stream and line-locked pixel clock from the video decoder.


(Click to enlarge)

10. Processor connection to video decoder from analog source

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