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AD9397KSTZ-100 Fiches technique(PDF) 11 Page - Analog Devices |
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AD9397KSTZ-100 Fiches technique(HTML) 11 Page - Analog Devices |
11 / 28 page AD9397 Rev. 0 | Page 11 of 28 TIMING The output data clock signal is created so that its rising edge always occurs between data transitions and can be used to latch the output data externally. Figure 3 shows the timing operation of the AD9397. tPER tDCYCLE tSKEW DATACK DATA HSOUT Figure 3. Output Timing HSYNC TIMING Horizontal sync (HSYNC) is processed in the AD9397 to eliminate ambiguity in the timing of the leading edge with respect to the phase-delayed pixel clock and data. The HSYNC input is used as a reference to generate the pixel sampling clock. The sampling phase can be adjusted, with respect to HSYNC, through a full 360° in 32 steps via the phase adjust register (to optimize the pixel sampling time). Display systems use HSYNC to align memory and display write cycles, so it is important to have a stable timing relationship between the HSYNC output (HSOUT) and data clock (DATACK). VSYNC FILTER AND ODD/EVEN FIELDS The VSYNC filter is used to eliminate spurious VSYNCs, maintain a consistent timing relationship between the VSYNC and HSYNC output signals, and generate the odd/even field output. The filter works by examining the placement of VSYNC with respect to HSYNC and, if necessary, slightly shifting it in time at the VSOUT output. The goal is to keep the VSYNC and HSYNC leading edges from switching at the same time, eliminating confusion as to when the first line of a frame occurs. Enabling the VSYNC filter is done with Register 0x21[5]. Use of the VSYNC filter is recommended for all cases, including interlaced video, and is required when using the HSYNC per VSYNC counter. Figure 4 and Figure 5 illustrate even/odd field determination in two situations. FIELD 1 FIELD 0 SYNC SEPARATOR THRESHOLD FIELD 1 FIELD 0 23 2 1 44 31 HSIN VSIN VSOUT O/E FIELD EVEN FIELD QUADRANT Figure 4. VSYNC Filter FIELD 1 FIELD 0 SYNC SEPARATOR THRESHOLD FIELD 1 FIELD 0 23 2 1 44 31 HSIN VSIN VSOUT O/E FIELD ODD FIELD QUADRANT Figure 5. VSYNC Filter—Odd/Even DVI RECEIVER The DVI receiver section of the AD9397 allows the reception of a digital video stream compatible with DVI 1.0. Embedded in this data stream are HSYNCs, VSYNCs, and display enable (DE) signals. DVI restricts the received format to RGB, but the inclusion of a programmable color space converter (CSC) allows the output to be tailored to any format necessary. With this, the scaler following the AD9397 can specify that it always wishes to receive a particular format—for instance, 4:2:2 YCrCb—regardless of the transmitted mode. If RGB is sent, the CSC can easily convert that to 4:2:2 YCrCb while relieving the scaler of this task. DE GENERATOR The AD9397 has an onboard generator for DE, for start of active video (SAV), and for end of active video (EAV), all of which are necessary for describing the complete data stream for a BT656-compatible output. In addition to this particular output, it is possible to generate the DE for cases in which a scaler is not used. This signal alerts the following circuitry as to which are displayable video pixels. |
Numéro de pièce similaire - AD9397KSTZ-100 |
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Description similaire - AD9397KSTZ-100 |
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