Difference between revisions of "VGAX49"

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[[File:tindie-mediums.png|link=https://www.tindie.com/products/land_boards/ps2-keyboardmouse-adapter-pcb-only-ps2x49/]]
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[[File:VGAX49_P901-cropped-720px.jpg]]
 
[[File:VGAX49_P901-cropped-720px.jpg]]
  
 
== Features ==
 
== Features ==
  
* Digital VGA adapter
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* Analog VGA adapter
* 16-bit digital video
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* Up to 16-bit digital video
** 5:6:5 (R:G:B) mapping (maximum)
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** 5:6:5 (R:G:B) mapping (maximum- 16 bits)
** 2:2:2 (R:G:B) mapping (option)
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** 3:3:2 (R:G:B) mapping (option - 8 bits)
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** 2:2:2 (R:G:B) mapping (option - 6 bits)
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** 1:2:1 (R:G:B) mapping (option - 4 bits)
 
* Uses summing resistors
 
* Uses summing resistors
 
* DB-15F connector
 
* DB-15F connector
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=== J1 - Digital Connections ===
 
=== J1 - Digital Connections ===
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 +
[[file:VGAX49_J1.PNG]]
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* Ex: R0 is the least significant Red bit (connects to 10K resistor)
  
 
=== P1 - VGA connector ===
 
=== P1 - VGA connector ===
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* Too much effort is put into using precision resistors - the human eye is not that picky
 
* Too much effort is put into using precision resistors - the human eye is not that picky
  
== VGA - Ideal Drive 2:2:2 Case ==
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== VGA - Ideal Drive 2 bit Case ==
  
 
* 3.3V driver requires less than 8 mA
 
* 3.3V driver requires less than 8 mA
** Some FPGAs need to have output configured as 3.3V LVTTL and 8mA drive current
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** Configure FPGAs output as 3.3V LVTTL and 8mA drive current
 
* Ideal case drive current
 
* Ideal case drive current
 
* Full scale video = 0.7V
 
* Full scale video = 0.7V
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[[File:VGA_Sim_2R_Current.PNG]]
 
[[File:VGA_Sim_2R_Current.PNG]]
  
=== 5:6:5 Resistor Simulation ===
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 +
== VGA - Ideal Drive 3 bit Case ==
 +
 
 +
* 3.3V driver requires less than 8 mA
 +
** Configure FPGAs output as 3.3V LVTTL and 8mA drive current
 +
* Ideal case drive current
 +
* Full scale video = 0.7V
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* VGA Termination resistor = 75 Ohms
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** 0.7V into 75 Ohms = 9.33 mA
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* R-2R values
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** 5% resistor values are 470 ohms, 1K ohms and 2.2K ohms
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*** Produces 0.697V
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[[file:VideoDAC_3bit_Voltage.PNG]]
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== 5:6:5 Resistor Simulation ==
  
 
* Assumptions
 
* Assumptions

Latest revision as of 13:43, 14 July 2022

Tindie-mediums.png

VGAX49 P901-cropped-720px.jpg

Features

  • Analog VGA adapter
  • Up to 16-bit digital video
    • 5:6:5 (R:G:B) mapping (maximum- 16 bits)
    • 3:3:2 (R:G:B) mapping (option - 8 bits)
    • 2:2:2 (R:G:B) mapping (option - 6 bits)
    • 1:2:1 (R:G:B) mapping (option - 4 bits)
  • Uses summing resistors
  • DB-15F connector
  • 49x49mm ODAS form factor
  • Mounting holes

Connectors

VGAX49.PNG

J1 - Digital Connections

VGAX49 J1.PNG

  • Ex: R0 is the least significant Red bit (connects to 10K resistor)

P1 - VGA connector

Simulation

  • Each color is independently driven and can be considered individually
  • Critical design criteria is output voltage and current capability of the driving part
  • Use common value, 5% resistors
  • Each resistor is about 2X the value of the previous resistor
  • 1V is drive level for VGA specification
    • VGA presents a 75 Ohm load
    • 1V at 75 Ohms is 13.3 mA
  • Series resistors present a voltage divider between the resistors on the card and the VGA load
  • The resistor with the smallest resistance value has larger current from the source device pin
  • Current switches from source to sink depending on the voltages on the other resistors
  • Each resistor is 2X the value of the previous resistor
  • Too much effort is put into using precision resistors - the human eye is not that picky

VGA - Ideal Drive 2 bit Case

  • 3.3V driver requires less than 8 mA
    • Configure FPGAs output as 3.3V LVTTL and 8mA drive current
  • Ideal case drive current
  • Full scale video = 0.7V
  • VGA Termination resistor = 75 Ohms
    • 0.7V into 75 Ohms = 9.33 mA
  • R-2R values
  • Voltage steps are:

VGA Sim 2R Voltage.PNG

  • Current steps are:

VGA Sim 2R Current.PNG


VGA - Ideal Drive 3 bit Case

  • 3.3V driver requires less than 8 mA
    • Configure FPGAs output as 3.3V LVTTL and 8mA drive current
  • Ideal case drive current
  • Full scale video = 0.7V
  • VGA Termination resistor = 75 Ohms
    • 0.7V into 75 Ohms = 9.33 mA
  • R-2R values
    • 5% resistor values are 470 ohms, 1K ohms and 2.2K ohms
      • Produces 0.697V

VideoDAC 3bit Voltage.PNG

5:6:5 Resistor Simulation

  • Assumptions
    • 3.3V Drive out of FPGA
    • 8 mA max drive current (typical FPGA drive current)
  • Using common value, 5% resistors
  • Model most significant bit resistor as 1/2 the full scale voltage (0.7V) single resistor value
  • 75 Ohm terminator in monitor
  • 0.7V at 75 Ohms = 9.33mA
  • Series resistor - single resistor value is (3.3V-0.7V)/9.33mA is 278.6 Ohms
  • First resistor is 2x 278.57 = 557.1 Ohms
  • Each resistor is 2x the previous resistor
  • Simulation uses the same 4 value steps (real case would have 2^5 or 2^6 steps)
  • Voltage steps

VideoDAC 6bit Voltage.PNG

  • Current steps

VideoDAC 6bit Current.PNG

Schematic

Assembly Sheet