Is RGB/SCART blanking signal (Pin 16) too low on some Cores? <1v

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Higgy
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Is RGB/SCART blanking signal (Pin 16) too low on some Cores? <1v

Postby Higgy » Sat Sep 29, 2018 6:14 pm

Hi.

I swapped my trusty Panasonic 14" CRT for a Sony Trinitron 14" CRT and I am having problems with it holding RGB/SCART mode.

I have narrowed it down to the voltage being outputted in RGB mode on the MiST.

For example MiniMig & Amstrad Cores output a measured 1V on VSYNC.
'Menu' Core and Sam Coupe output 0.76V on VSYNC.
This means the Sony TV only holds RGB mode for 1 sec then looses the signal.

If this is not going to be a problem for other people's TV's can the VSYNC High Drive signal always be at least 1V please?

The SCART spec looks to be 1-3V on Pin 16 for switching RGB mode.

Thanks

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Re: Is RGB/SCART blanking signal (Pin 16) too low on some Cores? <1v

Postby slingshot » Sat Sep 29, 2018 8:04 pm

Higgy wrote:Hi.

I swapped my trusty Panasonic 14" CRT for a Sony Trinitron 14" CRT and I am having problems with it holding RGB/SCART mode.

I have narrowed it down to the voltage being outputted in RGB mode on the MiST.

For example MiniMig & Amstrad Cores output a measured 1V on VSYNC.
'Menu' Core and Sam Coupe output 0.76V on VSYNC.
This means the Sony TV only holds RGB mode for 1 sec then looses the signal.

If this is not going to be a problem for other people's TV's can the VSYNC High Drive signal always be at least 1V please?

The SCART spec looks to be 1-3V on Pin 16 for switching RGB mode.

Thanks



It is not possible to set the voltage, it is fully digital, either 1 or 0. 1 should be 3.3V without any load. Probably the TV's internal resistance varies by the other signals it receives, so sometimes it draws more current, sometimes less. You can change the limiting resistor on the board (R16 as I see) to a smaller one, but if it's 100 ohm, as on the schematic, I don't recommend it, since if there's a short-circuit, you can fry the FPGA output pin.

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Re: Is RGB/SCART blanking signal (Pin 16) too low on some Cores? <1v

Postby DrOG » Sun Sep 30, 2018 5:25 am

Hi!

Some TVs need a standard voltage value on pin 8 to work reliably (this in unconnected if you use a standard minimig2scart cable):

Pin 8 - Status & Aspect Ratio
0–2 V → off
+5–8 V → on/16:9
+9.5–12 V → on/4:3


I wrote about my experiences earlier in another topic, read the next few post from here (sorry, linked pictures have been deleted):

viewtopic.php?f=115&t=28506#p312422

Hope it helps, it worths to try in my opinion.

Regards: Gábor

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Re: Is RGB/SCART blanking signal (Pin 16) too low on some Cores? <1v

Postby Sorgelig » Sun Sep 30, 2018 8:52 am

May be it's relative to output current set in QSF file for H/V Sync pins.

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Re: Is RGB/SCART blanking signal (Pin 16) too low on some Cores? <1v

Postby slingshot » Sun Sep 30, 2018 9:02 am

Sorgelig wrote:May be it's relative to output current set in QSF file for H/V Sync pins.

That's possible, SamCoupe has 4mA set, the Amstrad core doesn't have this set, so probably the default is 8mA.

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Re: Is RGB/SCART blanking signal (Pin 16) too low on some Cores? <1v

Postby Higgy » Sun Sep 30, 2018 9:21 am

Sorgelig - what is the current set on your Menu Core? As this also drops out with 0.76V being measured.

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Re: Is RGB/SCART blanking signal (Pin 16) too low on some Cores? <1v

Postby Sorgelig » Sun Sep 30, 2018 12:35 pm

Code: Select all

set_instance_assignment -name CURRENT_STRENGTH_NEW 4MA -to VGA_HS
set_instance_assignment -name CURRENT_STRENGTH_NEW 4MA -to VGA_VS

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Re: Is RGB/SCART blanking signal (Pin 16) too low on some Cores? <1v

Postby Higgy » Sun Sep 30, 2018 9:20 pm

So it looks like the default 8mA gives a measured voltage of 1V.

For my Sony I have now taken 5V off the TV PCB and via a resistor feed it to Pin 16 so it always forced RGB mode. Then Composite signals were not recognised! so I have added a toggle switch near the SCART socket to Force RGB on/off.

I guess my Panasonic CRT had a lower voltage threshold for RGB switching so I never saw a problem previously. I have also a Samsung 14" and Bush 20" but never tried the MiST with those.

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Re: Is RGB/SCART blanking signal (Pin 16) too low on some Cores? <1v

Postby slingshot » Mon Oct 01, 2018 10:54 am

Higgy wrote:So it looks like the default 8mA gives a measured voltage of 1V.

As you was already successful compiling SamCoupe, you can easily try out this on the Menu core for example, just clone the repo, change

Code: Select all

set_instance_assignment -name CURRENT_STRENGTH_NEW 4MA -to VGA_HS
set_instance_assignment -name CURRENT_STRENGTH_NEW 4MA -to VGA_VS

to

Code: Select all

set_instance_assignment -name CURRENT_STRENGTH_NEW "MAXIMUM CURRENT" -to VGA_HS
set_instance_assignment -name CURRENT_STRENGTH_NEW "MAXIMUM CURRENT" -to VGA_VS

in menu.qsf, recompile, and try out. Eventually you can send a pull request with the change. No VHDL or Verilog knowledge is required.


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