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AD9984A Datasheet(PDF) 9 Page - Analog Devices |
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AD9984A Datasheet(HTML) 9 Page - Analog Devices |
9 / 44 page AD9984A Rev. 0 | Page 9 of 44 Table 5. Pin Function Descriptions Mnemonic Function Description RAIN0 Analog Input for the Red Channel 0 GAIN0 Analog Input for the Green Channel 0 B B AIN0 Analog Input for the Blue Channel 0 RAIN1 Analog Input for the Red Channel 1 GAIN1 Analog Input for the Green Channel 1 B B AIN1 Analog Input for the Blue Channel 1 These high impedance inputs accept the red, green, and blue channel graphics signals, respectively. The three channels are identical and can be used for any colors, but colors are assigned for convenient reference. They accommodate input signals ranging from 0.5 V to 1.0 V full scale. Signals should be ac-coupled to these pins to support clamp operation. Refer to Figure 4 and Figure 5. HSYNC0 Horizontal Sync Input Channel 0 HSYNC1 Horizontal Sync Input Channel 1 These inputs receive a logic signal that establishes the horizontal timing reference and provides the frequency reference for pixel clock generation. The logic sense of these pins can be automatically determined by the chip or manually controlled by Serial Register 0x12, Bits[5:4] (Hsync polarity). Only the leading edge of Hsync is used by the PLL; the trailing edge is used in clamp timing. When Hsync polarity = 0, the falling edge of Hsync is used. When Hsync polarity = 1, the rising edge is active. These inputs include a Schmitt trigger for noise immunity. VSYNC0 Vertical Sync Input Channel 0 VSYNC1 Vertical Sync Input Channel 1 These inputs for vertical sync provide timing information for generation of the field (odd/even) and internal coast generation. The logic sense of this pin can be automatically determined by the chip or manually controlled by Serial Register 0x14, Bits[5:4] (Vsync polarity). SOGIN0 Sync-on-Green Input Channel 0 SOGIN1 Sync-on-Green Input Channel 1 These inputs help process signals with embedded sync, typically on the green channel. These pins connect to a high speed comparator with an internally generated threshold. The threshold level can be programmed in 8 mV steps to any voltage between 8 mV and 256 mV above the negative peak of the input signal. The default voltage threshold is 128 mV. When connected to an ac-coupled graphics signal with embedded sync, a noninverting digital output is produced on SOGOUT. This output is usually a composite sync signal, containing both vertical and horizontal sync information that must be separated before passing the horizontal sync signal for Hsync processing. When not used, these inputs should be left unconnected. For more details about this function and how it should be configured, refer to the Sync-on-Green section. CLAMP External Clamp Input (Optional) This logic input can be used to define the time during which the input signal is clamped to ground or midscale. It should be exercised when the reference dc level is known to be present on the analog input channels, typically during the back porch of the graphics signal. The CLAMP pin is enabled by setting the control bit clamp function to 1, (Register 0x18, Bit 4; default is 0). When disabled, this pin is ignored and the clamp timing is determined internally by counting a delay and duration from the trailing edge of the Hsync input. The logic sense of this pin can be automatically determined by the chip or controlled by clamp polarity (Register 0x1B, Bits[7:6]). When not used, this pin can be left unconnected (there is an internal pull-down resistor) and the clamp function programmed to 0. EXTCK/COAST External Clock (EXTCK) This pin has dual functionality. EXTCK allows the insertion of an external clock source rather than the internally generated, PLL locked clock. EXTCK is enabled by programming Register 0x03, Bit 2 to 1. This EXTCK function does not affect the COAST function. Optional Coast Input to Clock Generator (COAST) COAST can be used to cause the pixel clock generator to stop synchronizing with Hsync and continue to produce a clock at its current frequency and phase. This is useful when processing signals from sources that fail to produce Hsync pulses during the vertical interval. The coast signal is generally not required for PC-generated signals. The logic sense of this pin can be determined automatically or controlled by coast polarity (Register 0x18, Bits[7:6]). When this function and the EXTCK function are not used, this pin can be grounded and coast polarity programmed to 1. Input coast polarity defaults to 1 at power-up. This COAST function does not affect the EXTCK function. PWRDN Power-Down Control (PWRDN) PWRDN allows for manual power-down control. If manual power-down control is selected (Register 0x1E, Bit 4),and this pin is not used, it is recommended to set the pin polarity (Register 0x1E, Bit 2) to active high and hardwire this pin to ground with a 10 kΩ resistor. REFLO, REFHI Input Amplifier Reference REFLO and REFHI are connected together through a 10 μF capacitor. These are used for stability in the input ADC circuitry. See Figure 6. |
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