XiAleste -- Another Amstrad CPC6128 replica

Started by h2w, 15:19, 12 December 22

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TotO

@HAL6128 As I know, most of the colourful CGA demo are based on a composite NTSC trick.
So, it is not related to what I have posted about a GateArray with a RGBI output.
"You make one mistake in your life and the internet will never let you live it down" (Keith Goodyer)

h2w

I do not see the problem of the color expansion. The A520Ex used 6 bits direct RGB color value instead of some abstract number. It can't render exactly same colors as CPC128 but who cares the analog monitors were not much equal by the color rendition. For XiA will be used port shadowing and it will allow to have minimally RGB332 up to RGB888 on HDMI.
Or maybe I am missing something?

TotO

#27
The Aleste 520EX has a ROM to remap the CPC index from 6-bit RGB. There is no problem to redo the same, it will work. I'm just answering how a real GateArray in a CPC could have increased the number of colors while remaining compatible, that's all. :)

@MacDeath isn't here, so I post this pic, as I know he likes to do this kind of things. Next, I no more "spoil" your topic. :-*
"You make one mistake in your life and the internet will never let you live it down" (Keith Goodyer)

PulkoMandy

A real Gate Array is a purely binary chip, we are lucky that Amstrad went a bit creative and tought of using high impedence to add a 3rd level, otherwise we'd have only 8 colors.

Adding an intensity bit would require one more pin on the package, which is not possible because the Gate Array is based on a standard "Gate Array" system that has only a fixed number of input and output pins. So, which one of those existing pins would you remove to make space for your new intensity output?


Sykobee (Briggsy)

They were planning on 64 colours with an external resister ladder I believe, but they ran out of pins as PM says - it was very lucky that GA supported stable tristate outputs on a few pins.
Obviously they could have used a slightly bigger GA, but that didn't fit in the cost-cutting ethos :)

TotO

#30
Quote from: PulkoMandy on 21:43, 05 January 23A real Gate Array is a purely binary chip, we are lucky that Amstrad went a bit creative and tought of using high impedence to add a 3rd level, otherwise we'd have only 8 colors.
Sure, it was a great alternative to not have 8 colours like some other computers.
It was not possible to have 3 extra pins (RRGGBB) and twice the registers to store the colour index.

Quote from: PulkoMandy on 21:43, 05 January 23Adding an intensity bit would require one more pin on the package, which is not possible because the Gate Array is based on a standard "Gate Array" system that has only a fixed number of input and output pins. So, which one of those existing pins would you remove to make space for your new intensity output?
Show me the base package to be sure than all the pins are used, and not one free tied to GND.

Anyway, the first GA (40007) was not designed for the Z80 and must provide the RAM refresh. With the design update (40010) it was probably possible to use the Z80 /RFSH pin to do the job, if really required by Amstrad to save a pin. (probably other options exist)

EDIT: Taking a look to the decaped 40010, there are 4x18 (72) i/o pins, 35 are used, 2 linked to VCC, 1 tied to GND. 2 true GND.
"You make one mistake in your life and the internet will never let you live it down" (Keith Goodyer)

SerErris

The refresh in the CPCs is done by the CRTC setting all 256 row addresses ever 50 mseconds, not the GA. The GA is used to create the clocks (and the video clock bit is used to access video RAM). 

But again, the CRTC is creating the all the row addresses to refresh the RAM.

Anyhow not important for the discussion here. If there would have been anything available to produce a intensity bit easily with the existing resources - they would have done it.
Proud owner of 2 Schneider CPC 464, 1 Schneider CPC 6128, GT65 and lots of books
Still learning all the details on how things work.

GUNHED

Guys, please stay on topic! 

The XiAleste is an alternative to our beloved, but sold-out CPCs / Plus computers.
General discussions are welcome of course - in their own threads.

Here - please - lets focus on the topic. 

Coming back to my question: Thanks h2w, extended GFX features are not excluded. Good to hear.  :)

Will somebody actually go to produce the XiAleste?
For some of us it would be great to be able to buy the final product and invest time into programming for the XiAleste.  :)
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h2w

#33
Quote from: GUNHED on 15:25, 06 January 23Will somebody actually go to produce the XiAleste?
For some of us it would be great to be able to buy the final product and invest time into programming for the XiAleste.  :)
1. I am planning to build as minimum one unit. I don't do it right now only because I do not have budged for. I am seeking job at this moment, so as soon I will found one I will order first 3-4 PCBs.

2. I can build limited quantity 10 units with very small profit - if there will be such order.

The biggest issue right now the FPGA, I need for find somebody to assist. In other case the project schedule will be extended.

h2w

The schematic circuit and PCB files uploaded to github. Please feel free to report: design mistakes, any kind of errors include spell-errors in the schematics. Feel free to collaborate and recommend me ECOs.  :)

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