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CS4955-CQ Fiches technique(PDF) 11 Page - Cirrus Logic |
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CS4955-CQ Fiches technique(HTML) 11 Page - Cirrus Logic |
11 / 56 page CS4954 CS4955 DS278PP4 11 The CS4954/5 is designed to function as a video timing master or video timing slave. In both Master and Slave Modes, all timing is sampled and assert- ed with the rising edge of the CLK pin. In most cases, the CS4954/5 will serve as the video timing master. HSYNC, VSYNC, and FIELD are configured as outputs in Master Mode. HSYNC or FIELD can also be defined as a composite blanking output signal in Master Mode. In Master Mode, the timing of HSYNC, VSYNC, FIELD and Compos- ite Blank (CB) signals is programmable. Exact hor- izontal and vertical display timing is addressed in the Operational Description section. In Slave Mode, HSYNC and VSYNC are typically configured as input pins and are used to initialize independent vertical and horizontal timing genera- tors upon their respective falling edges. HSYNC and VSYNC timing must conform to the ITU- R BT.601 specifications. The CS4954/5 also provides a ITU R.BT656 Slave Mode in which the video input stream contains EAV and SAV codes. In this case, proper HSYNC and VSYNC timing are extracted automatically without any inputs other than the V [7:0]. ITU R.BT656 input data is sampled with the leading edge of CLK. In addition, it is also possible to output HSYNC and VSYNC signals during CCIR-656 Slave Mode. 4.2. Video Input Formatter The Video Input Formatter translates YCbCr input data into YUV information, when necessary, and splits the luma and chroma information for filter- ing, scaling, and modulation. 4.3. Color Subcarrier Synthesizer The subcarrier synthesizer is a digital frequency synthesizer that produces the appropriate subcarri- er frequency for NTSC or PAL. The CS4954/5 generates the color burst frequency based on the CLK input (27 MHz). Color burst accuracy and stability are limited by the accuracy of the 27 MHz input. If the frequency varies, then the color burst frequency will also vary accordingly. For environments in which the CLK input varies or jitters unacceptably, a local crystal frequency refer- ence can be used on the XTAL_IN and XTAL_OUT pins. In this instance, the input CLK is continuously compared with the external crystal ref- erence input and the internal timing of the CS4954/5 is automatically adjusted so that the color burst fre- quency remains within tolerance. Controls are provided for phase adjustment of the burst to permit color adjustment and phase com- pensation. Chroma hue control is provided by the CS4954/5 via a 10-bit Hue Control Register (HUE_LSB and H_MSB). Burst amplitude control is also made available to the host via the 8-bit burst amplitude register (SC_AMP). 4.4. Chroma Path The Video Input Formatter delivers 4:2:2 YUV outputs into separate chroma and luma data paths. The chroma path will be discussed here. The chroma output of the Video Input Formatter is directed to a chroma low-pass 19-tap FIR filter. The filter bandwidth is selected (or the filter can be bypassed) via the CONTROL_1 Register. The passband of the filter is either 650 KHz or 1.3 MHz and the passband ripple is less than or equal to 0.05 dB. The stopband for the 1.3 MHz selection begins at 3 MHz with an attenuation of greater than 35 dB. The stopband for the 650 KHz selection be- gins around 1.1 MHz with an attenuation of greater than 20 dB. The output of the chroma low-pass filter is connect- ed to the chroma interpolation filter in which up- sampling from 4:2:2 to 4:4:4 is accomplished. Following the interpolation filter, the U and V chroma signals pass through two independent vari- able gain amplifiers in which the chroma amplitude |
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