exxos's Atari, Amiga & retro forum

exxos wrote: 24 Sep 2018 17:15 Mux are easy enough. Really just 2 buffers in parallel, just enable one or the other set of buffers. RGB on one set of inputs, MONO on all RGB inputs on the second buffer. I think its basically what the UBE does.

Well my point is to not enabling one or the other, but both. I.e, with a compatible screen you should just be able to display a color or mono mode just like switching between any other resolutions. No manual switch needed.

(An automatic switch could be done by listening on ff8260/1, if that's really easier)

The MUXes need to be analog MUXes for the RGB .... unless you're muxing the shifter output to the resistor ladder.

rpineau wrote: 24 Sep 2018 17:34 The MUXes need to be analog MUXes for the RGB .... unless you're muxing the shifter output to the resistor ladder.

I hadn't even thought about doing it digital. That might be really easy.

(The Shifter revision with analogue output is depicted on schematics but no one has ever been found in the wild, nor as a board revision)

troed wrote: 24 Sep 2018 17:23 Well my point is to not enabling one or the other, but both. I.e, with a compatible screen you should just be able to display a color or mono mode just like switching between any other resolutions. No manual switch needed.

(An automatic switch could be done by listening on ff8260/1, if that's really easier)

You mean wiring the RGB to mono directly ? It couldn't be done without a mux, and a mux needs A/B select. You can't multiplex MONO onto the RGB, as if mono is high or low all the RGB drivers would follow that signal.

The composite sync is a basic mux which I think you are talking about, but if you mux "HI" (assuming MONO output is high in RGB modes) then the output would be HI and you wouldn't get RGB data anymore, only mono.

rpineau wrote: 24 Sep 2018 17:34 The MUXes need to be analog MUXes for the RGB .... unless you're muxing the shifter output to the resistor ladder.

This is what Urban uses for RGB buffering and select..

https://www.ti.com/lit/ds/symlink/ts5v330.pdf

So there are proper mux for analouge signals. It could probably be done before the resistor ladder, might be better to switch the digital side of things rather than analouge anyway.

troed wrote: 24 Sep 2018 17:23 (An automatic switch could be done by listening on ff8260/1, if that's really easier)

If we can enable Hi res in desktop menu, then if setup right, we would need a control bit to switch mono detect line low.. we also should think about not removing the normal mono detect signal either.. We can probably do a OR function, detect as i n"classic mono detect" via the mono detect pin on the monitor port, or enable the switch from a register in software. But of course will need some PLD decoding to do it.

exxos wrote: 24 Sep 2018 17:44 You mean wiring the RGB to mono directly ? It couldn't be done without a mux, and a mux needs A/B select. You can't multiplex MONO onto the RGB, as if mono is high or low all the RGB drivers would follow that signal.

Right, haven't spent too much time into what's high and low. Op-amps (summing adder) seem to be able to combine two analogue signals and that's about as far down that path I've gone. Still an electronics newb, and esp. when it comes to the analogue parts :)

Combining digital output from the Shifter is a whole different matter though, I'll think a bit more on that. I really want for this to be switch-less to function the way I imagined it. I.e, with Czietz' new video tricks there's a cool new resolution with color timings (50/60Hz, 15.7kHz) but with _mono_ output from the Shifter.

troed wrote: 24 Sep 2018 18:05 Combining digital output from the Shifter is a whole different matter though, I'll think a bit more on that. I really want for this to be switch-less to function the way I imagined it. I.e, with Czietz' new video tricks there's a cool new resolution with color timings (50/60Hz, 15.7kHz) but with _mono_ output from the Shifter.

I don't know much about those fancy video tricks. Though I don't think you can multiplex mono and colour at the same time without one conflicting with each other. The RGB drivers can be switch for MONO OR COLOUR, and can be switched either on the mono detect input pin, or via a register, or both.

The question really though in that respect, such "tricks" shouldn't be needed once the HDMI board has more modes built into it.. Once we get higher MMU speeds, we can pretty much do anything we want with the video, only with proper resolution modes, not fancy tricks to do it..

Yes. I was thinking of feeding the R[0..2], G[0..2] and B[0..2] from the shifter into muxes. These are digital 0/1 output, not analog, then feed the output of these mux to the resistor ladder. On the 2nd input of each mux you feed in the mono pin (to all of them).
Just a thought.
RoRo

So shifter outputs (digital) feed via tristate buffers..

Mono video goes via another tristate buffer. Which is feed back into the RGB drivers (analouge). Though will only be HI or LOW outputs. 1K resistor has to be there to limit brightness and prevent shorts with the blanking diodes.

MONO_DETECT is inverted, so either RGB or MONO video is feed to the RGB buffers.

I have made provisions for 4 bit RGB data, but only 4 lines used currently for obvious reasons.