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I'm working on a hardware project where I want my board to act as a VGA monitor, so it has a female VGA connector on it. Everything I can find online says that pins 11, 12, 4, 15, are used to identify what resolutions and frequencies the monitor supports (or that pins 12 and 15 are an I2C connection).

I just want my project to act as a boring VGA monitor, with resolution 640 x 480 @ 60Hz, but I can't find anything on what specific resistors or connections I need to apply to those pins so a computer would see it as a VGA monitor and start streaming the HSYNC, VSYNC, and RGB lines.

Is there anywhere I can find a standard on what the monitor ID pins are and what pull-up or pull-down resistors I need to connect to them?

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  • \$\begingroup\$ 640 x 480 may be the default setting when none of the pins are connected \$\endgroup\$
    – jsotola
    Commented Aug 26, 2023 at 21:50
  • \$\begingroup\$ Yup. That was the original, one-and-only VGA back in the day. \$\endgroup\$
    – TimWescott
    Commented Aug 26, 2023 at 21:51
  • \$\begingroup\$ I suggest that you just try a VGA output, looking at the lines with an oscilloscope. \$\endgroup\$
    – TimWescott
    Commented Aug 26, 2023 at 21:53
  • \$\begingroup\$ what-when-how.com/display-interfaces/… \$\endgroup\$
    – jsotola
    Commented Aug 26, 2023 at 21:59

1 Answer 1

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The ID pins have not been used as static ID pins for ages.

The I2C pins have been used for a long time for DDC bus, which can be used to read an I2C EEPROM for a data structure known as EDID.

The EDID in the monitor provides a list of supported video formats to PC.

DDC and EDID are standards that are available for reading so you should refer to them.

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  • \$\begingroup\$ Yes, while true, probably not so helpful to OP who probably doesn’t have the tools or skills to make the DDC EEPROM. \$\endgroup\$ Commented Aug 26, 2023 at 21:38
  • \$\begingroup\$ @hacktastical How so? Any standard I2C EEPROM will do, as long as it is small enough and at correct address. As for the contents, there are many EDID editor tools available from different vendors, or, in a pinch and not reading the EDID standard, even the EDID article on Wikipedia has almost enough info (even though I hate it when they edited the page for newest 1.4 format while most often 1.3 is the most common unless you use DisplayPort). \$\endgroup\$
    – Justme
    Commented Aug 26, 2023 at 21:55
  • \$\begingroup\$ Again, if just strapping (or not) gets what they want, why overcomplicate things? \$\endgroup\$ Commented Aug 26, 2023 at 23:07
  • \$\begingroup\$ @hacktastical Modern video outputs do not sense the straps and do not know what to output if there is no EDID so video drivers may not output anything and may not allow you to select a resolution. \$\endgroup\$
    – Justme
    Commented Aug 26, 2023 at 23:10
  • \$\begingroup\$ Thank you. I'll first try taking a gamble and hoping that the graphics card will detect the 75 Ohm resistors from the R/G/B pins to GND (this is what VGA Dummy Plugs seem to do). Failing that, i guess I'll have to use an EEPROM. \$\endgroup\$ Commented Aug 27, 2023 at 22:16

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