Difference between revisions of "Video DAC"

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[[File:mvs_viddac.jpg|right|thumb|Resistor array forming the video DAC on a 1FZS.]]
 
[[File:mvs_viddac.jpg|right|thumb|Resistor array forming the video DAC on a 1FZS.]]
  
The NeoGeo uses a discrete video DAC made of resistors and two 74LS273 latches which store the color value from the [[palette RAM]] while the pixel has to be displayed. This is controlled by either [[NEO-B1]], [[NEO-GRC]] or [[NEO-GRZ]].
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The NeoGeo uses a discrete video Digital-to-Analog Converter made of resistors and two 74LS273 latches which store the color value from the [[palette RAM]] while the pixel has to be displayed. This is controlled by either {{Chipname|NEO-B1}}, {{Chipname|NEO-GRC}} or {{Chipname|NEO-GRZ}}.
  
 
[[File:aes_viddac.png|right|thumb|Video DAC on a AES board.]]
 
[[File:aes_viddac.png|right|thumb|Video DAC on a AES board.]]
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Each color component has its own set of 7 resistors. 6 of them are used with the actual color value (5 + 1 [[Palettes|common bit]]). The last (SHADOW signal) is related to the {{Reg|REG_SHADOW}} and {{Reg|REG_NOSHADOW}} registers (74HC259 latch).
 
Each color component has its own set of 7 resistors. 6 of them are used with the actual color value (5 + 1 [[Palettes|common bit]]). The last (SHADOW signal) is related to the {{Reg|REG_SHADOW}} and {{Reg|REG_NOSHADOW}} registers (74HC259 latch).
  
The output voltage is then divided by 5 to obtain a 1Vp-p max signal, which can be fed to the [[CXA1145]] encoder.
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The output voltage is then divided by 2200 / (6800 + 2200) = 4.1 (considered Voh of 74LS ?), to obtain a 1Vp-p max signal, which can be fed to the [[video encoder]].
  
 
[[Category:Chips]]
 
[[Category:Chips]]
 
[[Category:Video system]]
 
[[Category:Video system]]

Revision as of 07:36, 17 January 2016

Resistor array forming the video DAC on a 1FZS.

The NeoGeo uses a discrete video Digital-to-Analog Converter made of resistors and two 74LS273 latches which store the color value from the palette RAM while the pixel has to be displayed. This is controlled by either NEO-B1, NEO-GRC or NEO-GRZ.

Video DAC on a AES board.

Aes viddac schematic.png

Each color component has its own set of 7 resistors. 6 of them are used with the actual color value (5 + 1 common bit). The last (SHADOW signal) is related to the REG_SHADOW and REG_NOSHADOW registers (74HC259 latch).

The output voltage is then divided by 2200 / (6800 + 2200) = 4.1 (considered Voh of 74LS ?), to obtain a 1Vp-p max signal, which can be fed to the video encoder.