MONO SWITCH

[exxos]

What this basically does is switch the RGB digital shifter outputs with the shifter MONO output via a multiplexer chips. Basically a simple "UBE Switch".

The selection between the 2 will be done via a jumper. I have no idea if this could be controlled via software or not ultimately. I guess if a PLD did a register, then a program could switch the register to enable MONO mode and reset the machine to do the change

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So shifter RGB goes via the 157 chips, then to the video DAC.

MONO also goes via the 157 chips to the video DAC.

The select between RGB / MONO is done via JP4.

[ube]

Have you tried this? For v3 I used 4051 as switch and ended up with a very dark image on RGB..

[exxos]

Have you tried this? For v3 I used 4051 as switch and ended up with a very dark image on RGB..

Nope. But I am only switching the digital side of things so it shouldn't affect anything.

[ube]

Of course! Carry on!

[MasterOfGizmo]

Many, MANY years ago i did something very similar on a real ST. See my old (german, google will help you) page at
http://www.harbaum.org/till/atari/multisync.html

This also includes links to schematics. This does:

* combine mono and color video signals into one rgb signal
* use a GAL to detect the video mode by measuring the hsync length and output color or mono based on this
* connect the mono sense pin with the gpio out on the video connector

Up to this point the whole setup behaves exactly like one of those old external "monitor switch boxes" that you could use to attach both a color and a mono screen at the same time and switch by sofware which would cause the ST to reboot with the new resolution.

But you could also use the "mono is active" signal generated by the GAL and feed that into the mono detect input on the video port. Then you could actually switch between all three video modes without the ST resetting/rebooting in between.

[exxos]

Interesting project and solution!