32768 color dual Shifter ST mod - schematics lost?

General discussions or ideas about hardware.
User avatar
mrbombermillzy
Posts: 1441
Joined: Sun Jun 03, 2018 7:37 pm

Re: 32768 color dual Shifter ST mod - schematics lost?

Post by mrbombermillzy »

I get most people are saying its not much use...

However, it's a 100% compatible upgrade for the poor 9-bit palette ST/F/M/Mega owners. (Can even be set up to emulate and extend the STe palette writing system, although if I were to suggest a design decision, I would put the colour order the same as the TT or Falcon, with matching colour bits together in value significance, e.g; R5G5B5 which would be ESSENTIAL for 'real time' palette change work, but would still be usable for STe compatible images; would still have to colour reduce, so may as well swap the colour bit significance around too for STe compatability if required).

Other than that, there are some options with Photochrome and other bits (which I myself am working on which can be re-targerted for this if it comes to fruition at all). Any changes to someone writing new code are pretty trivial to take advantage of the extra palette.

The only issue I see (other than can it be done?) is do we have many shifters, or are they also going the way of the later full 060s?
User avatar
sporniket
Posts: 956
Joined: Sat Sep 26, 2020 9:12 pm
Location: France
Contact:

Re: 32768 color dual Shifter ST mod - schematics lost?

Post by sporniket »

@Smonson yes, you understood the principles like me.

This is as useful as the 4096 colors of the STe compared to the 512 colors of the ST. I allows smoother color gradients, either created over a subset of the available color palette, or with raster effect.

The 4th bit is laid out like the STe, so that would give the same capability to the STF. The 5th bit plus the 6th green bit is more of an extra, and the bits arrangement is incompatible with the true color pixel of the falcon, so a conversion would still be required.

By the way, for the STe, it may possible, but not sure. And of course, the second shifter will be a STF shifter.

@Darklord yes, to me this is the same technique, limited to adding the 4th bit.

@Elliot yes, this mod adds a second STF Shifter, tasked with managing the extra bits to renders the colors components (rgb).
User avatar
mrbombermillzy
Posts: 1441
Joined: Sun Jun 03, 2018 7:37 pm

Re: 32768 color dual Shifter ST mod - schematics lost?

Post by mrbombermillzy »

@sporniket

Shouldn't it be R5 G5 B5?

Unless there's another bit in the mix that I've overlooked to give 65k colour palette? :)
User avatar
sporniket
Posts: 956
Joined: Sat Sep 26, 2020 9:12 pm
Location: France
Contact:

Re: 32768 color dual Shifter ST mod - schematics lost?

Post by sporniket »

Ha, yes you're right @mrbombermillzy, this is in my own reflections that I had also assigned the last unused bit into a 6th bit for green, inspired by the Falcon, and by the H5 as well for using the falcon's DAC.
User avatar
derkom
Moderator
Moderator
Posts: 1208
Joined: Sun Jul 29, 2018 6:45 pm

Re: 32768 color dual Shifter ST mod - schematics lost?

Post by derkom »

Oddly enough I have a distinct memory of reading the original document describing this upgrade while I was sitting in an ice cream parlour as a wee lad. What I wouldn't have given to have so many colours on my 520ST! And I'm pretty sure it had the schematics with it, but don't get any hopes up, as there's no chance of finding those files today. :roll:
User avatar
mrbombermillzy
Posts: 1441
Joined: Sun Jun 03, 2018 7:37 pm

Re: 32768 color dual Shifter ST mod - schematics lost?

Post by mrbombermillzy »

Ok, problem sorted then...

We send someone round to @derkom to perform deep regression hynotherapy and ask him to draw the schematics in detail! :lol:

Seriously though, on another point, unless someone can confirm seeing one EVER in real life, I don't know if one actually existed or it's still just an (unproven) concept? I know Barry wrote some demo code to test with, but there were never any photos of it displayed (which I thought would be a big thing back then and at least SOMEONE on a magazine staff or something would have taken a picture at some point).

So who knows...
User avatar
SophieRose
Posts: 33
Joined: Mon Dec 28, 2020 4:47 am
Location: Leamington Spa
Contact:

Re: 32768 color dual Shifter ST mod - schematics lost?

Post by SophieRose »

I've been interested in this mod for ages, would love to build one if someone can sort the schematics. 8-)

Purely because I do a bit of pixel art in dpaint and it would be good to use the STE palette on my main MegaST.
Musician and Atari ST user. https://sophie-rose.bandcamp.com
Mega ST4 T28, 1040STE & 520STM, Amiga 600, Link 480Z, Amstrad 6128 plus, Timex2048, C128, C64, MSX HB201P. Plus too many more.
User avatar
GadgetUK164
Posts: 430
Joined: Fri Jan 04, 2019 2:26 pm

Re: 32768 color dual Shifter ST mod - schematics lost?

Post by GadgetUK164 »

Yeah, I've thought about this mod for years! Problem now is trying to find a 2nd Shifter...
It might be easier to borrow VHDL (or whatever is used) from MiSTer and shove it into a CPLD or something?
My YouTube Channel - www.youtube.com/GadgetUK164
User avatar
mrbombermillzy
Posts: 1441
Joined: Sun Jun 03, 2018 7:37 pm

Re: 32768 color dual Shifter ST mod - schematics lost?

Post by mrbombermillzy »

Smonson wrote: Wed Dec 08, 2021 4:23 am During a pixel output the two shifters combined will then produce a 6-bits-per-colour output instead of the normal 3-bits-per-colour, which would normally be driven through a 3-bits-per-colour resistor DAC to convert to analogue on the ST mainboard, but in this case they're all routed to a new 6-bits-per-colour DAC here, and each of the resulting 3 analog colour outputs are injected into the mainboard using flying wires.
@Smonson Just re-read this. Forgive me, as I'm not a HW guy, but wouldn't what you just explained then create a physical 18-bit palette?

Obviously the palette registers 'max out' at 16 bits, but still...?
User avatar
sporniket
Posts: 956
Joined: Sat Sep 26, 2020 9:12 pm
Location: France
Contact:

Re: 32768 color dual Shifter ST mod - schematics lost?

Post by sporniket »

Just re-read what I wrote here : https://www.exxosforum.co.uk/forum/viewt ... 302#p75587

The "main" shifter receive color palette data and treats them as usual ie. 3 bits per channel r/g/b, those are the Most Significant Bits of each channel.

The "auxiliary" shifter, through a clever bit swapping only when setting palette colors, grabs the supplemental bits that are the Least Significant Bits of each channels. At best, with 16 bits (the width of the data bus), we can define a color with 5 bits for two channels, and 6 bits for the third one. I arbitrarily chose the same repartition than the Falcon (rgb565), because I read that this choice was made to accomodate the human vision that would be supposedly more sensitive to greens.

On the output side of the two shifters, all the bits from both shifter are recombined, with some of them ignored according to how we redirected each bit of the "full" palette color.

Then the remaining problem would be how to weight each value of r/g/b when converting to analog. It's eathier when all the channel have the same definition (333, 444 or 555). I could note that in the Falcon schematics, the DAC has 8bits per channel (rgb888), and for each channel, only the 6 MSB were wired to the Videl.

Anyway that's all for now. I will try -no promise- to make a proper schematic of all my thought this month. Then maybe I will layout a PCB, for those that want to try -and that have a test machine and a spare shifter-.

I do not rule out anything once my H5 is up and running, but frankly I plan to have get the "Shifter with native converted HDMI output".
Post Reply

Return to “HARDWARE DISCUSSIONS”