Difference between revisions of "Video DAC"

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(Added a note to the schematic and corrected the 74ls06 reference)
 
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[[File:mvs_viddac.jpg|right|thumb|Resistor array forming the video DAC on a 1FZS MVS board.]]
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[[File:mvs_viddac.jpg|right|thumb|Resistor array forming the video DAC on a [[MV1FZS]].]]
  
The NeoGeo video DAC was made by using digital latches and precision resistors.
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The NeoGeo uses a discrete video '''D'''igital-to-'''A'''nalog '''C'''onverter made of resistors fed by two [[74LS273|74LS273]] latches which store the color value from the [[palette RAM]] and [[74LS05|74LS05]] inverters. This is controlled by either {{Chipname|NEO-B1}}, {{Chipname|NEO-GRC}} or {{Chipname|NEO-GRZ}}.
  
TODO: Resistor values, schematic ?, "[[Dark bit]]"...
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[[File:aes_viddac.png|right|thumb|Video DAC on a AES board.]]
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[[File:aes_viddac_schematic.png]]
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Note: The schematic has a typo and shows a 74LS06 instead of [[74LS05|74LS05]] but both can be used.
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Each color component has its own set of 7 resistors. 6 of them are used for the actual color value (5 + 1 [[Colors|common bit]]). The last (SHADOW signal) is related to the {{Reg|REG_SHADOW}} and {{Reg|REG_NOSHADOW}} registers ([[system latch]]).
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==Arcade==
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The output isn't lowered like on the AES. It goes straight to the [[JAMMA connector pinout|JAMMA edge]] as a 0~3.5V signal for the high-impedance inputs on arcade monitors.
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==Home==
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The output is divided by 2200 / (6800 + 2200) = 4.1 to obtain a ~0.9Vp-p max signal, which feeds the [[video encoder]] for amplification and conversion to composite.
  
 
[[Category:Chips]]
 
[[Category:Chips]]
 
[[Category:Video system]]
 
[[Category:Video system]]

Latest revision as of 23:14, 16 May 2020

Resistor array forming the video DAC on a MV1FZS.

The NeoGeo uses a discrete video Digital-to-Analog Converter made of resistors fed by two 74LS273 latches which store the color value from the palette RAM and 74LS05 inverters. This is controlled by either NEO-B1, NEO-GRC or NEO-GRZ.

Video DAC on a AES board.

Aes viddac schematic.png

Note: The schematic has a typo and shows a 74LS06 instead of 74LS05 but both can be used.

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

Arcade

The output isn't lowered like on the AES. It goes straight to the JAMMA edge as a 0~3.5V signal for the high-impedance inputs on arcade monitors.

Home

The output is divided by 2200 / (6800 + 2200) = 4.1 to obtain a ~0.9Vp-p max signal, which feeds the video encoder for amplification and conversion to composite.