MiSTer FPGA Forum

I feel like this has been discussed all over the place, but I couldn't find a final answer. Could someone please clarify:

I have an IO board and want to connect my Sony BVM through a VGA to BNC cable. In the MiSTer Wiki, the disclaimer in the Direct Video section talks about VGA DACs outputting a sync signal of 3 volts or more on pin 13. They then suggest to use the cable from Retro Access (which isn't really available).

So, my questions is: Does the VGA port on the IO Board output 3 volts as well and do I need to have a special VGA to BNC cable that attenuates the sync signal?

I don't want to damage my BVM, so I'm extra careful. Maybe someone could point me to a source where I can buy the best cable for this purpose (ideally from Europe but doesn't matter too much)? I believe my BVM requires a composite sync.

Thanks!

Direct Video is for the HDMI port. If you have an IO board, a regular VGA to BNC adapter is enough; I use that with my PVM. You may need to set an INI setting to get the right sync, but that's it.

The disclaimer is there on the wiki because on how some HDMI to VGA DACs work. The IO board does not have those problems, though.

HDMI to VGA DACs output 3.3 - 5v usually with 75 Ohm impedance. Together with 75Ohm termination the resulting voltage will be 1.65v - 2.5v.

The IO board outputs 3.3v through a 100 Ohm resistor. Together with 75 Ohm termination the voltage is 1.4v.

It depends on the sync voltage requirements of your BVM whether or not you should attenuate the sync signal. If you want to be extra careful then the cable should have a minimum of 470 Ohm resistor.

Thanks for the feedback.

I have a BVM-20F1E and just checked the manual. It says:
"Sync input: BNC type, 1 (with loop-through output). Composite sync: 0.3 to 8 Vp-p, negative, high impedance"

I suppose this means I can connect with the IO board or through a HDMI to VGA DAC without worry?

VGA to BNC cables that have a 470 Ohm resistor are nowhere to be found, so I hope the above is the case.

Silly question: I have always used hdmi on my mister

If I want to use vga -> component cable, do I have to change some value on mister.ini? Where?

Another-Frank wrote: ↑Thu Mar 18, 2021 10:44 am I suppose this means I can connect with the IO board or through a HDMI to VGA DAC without worry?

Yeah if it can handle up to 8v then you can use a cable without resistor.

pbsk8 wrote: ↑Thu Mar 18, 2021 3:35 pm Silly question: I have always used hdmi on my mister

If I want to use vga -> component cable, do I have to change some value on mister.ini? Where?

ypbpr=1 and you might have to adjust the SoG switch on the IO board depending on the version.

paulbnl wrote: ↑Thu Mar 18, 2021 8:30 pm

Another-Frank wrote: ↑Thu Mar 18, 2021 10:44 am I suppose this means I can connect with the IO board or through a HDMI to VGA DAC without worry?

Yeah if it can handle up to 8v then you can use a cable without resistor.

pbsk8 wrote: ↑Thu Mar 18, 2021 3:35 pm Silly question: I have always used hdmi on my mister

If I want to use vga -> component cable, do I have to change some value on mister.ini? Where?

ypbpr=1 and you might have to adjust the SoG switch on the IO board depending on the version.

mine is v6.0, it is set all the time to OVR all the time. Actually I dont even know the meaning for this switch so far.

pbsk8 wrote: ↑Thu Mar 18, 2021 10:10 pm

paulbnl wrote: ↑Thu Mar 18, 2021 8:30 pm

Another-Frank wrote: ↑Thu Mar 18, 2021 10:44 am I suppose this means I can connect with the IO board or through a HDMI to VGA DAC without worry?

Yeah if it can handle up to 8v then you can use a cable without resistor.

pbsk8 wrote: ↑Thu Mar 18, 2021 3:35 pm Silly question: I have always used hdmi on my mister

If I want to use vga -> component cable, do I have to change some value on mister.ini? Where?

ypbpr=1 and you might have to adjust the SoG switch on the IO board depending on the version.

mine is v6.0, it is set all the time to OVR all the time. Actually I dont even know the meaning for this switch so far.

It's for sync on green monitors.

TV's on their RGB inputs almost always use the composite signal as the sync signal alongside the three colours.

Most VGA monitors use what's called RGBHV (horizontal vertical sync) so they have five conductors/cables one each for each colour, the other two for the H and V syncs. SOG monitors have four cables (I believe), one cable each for the Red and Blue and two for the Green signal, one cable also has the Hsync the other the Vsync... Hence "sync on green".

This switch would only be needed when using a SOG monitor, using it with any other type will just make the image look green.