Amiga and expansion boards

[whitebird]

Hello,

I've got an A1200 motherboard, so I am thinking of some towering project.

I have a question about how the system works when a PCI VGA board is used (through PCI mediator for ex...) with a CPU board (like a an M-TEC 1230 for ex).

I would like to know what is the task of the 1200 mainboard in that case.

Is the mainboard used only for OS storage and I/O like disks and keyboard. Because if the RAM, CPU and video is on daughter boards, then A1200 mainboard has few tasks for itself??

What about the graphics, does the PCI VGA board completely replace the custom chips, so we loose the hardware scrolling and so on, or can the graphics card be used only like a VGA output so we can still take advantages of the amiga custom chips, and eventually mix them with a 3D GPU to produce some hybrid graphics??

Thanks in advance for answering me.

[ajk]

PC graphics cards are not designed to pass through the Amiga native screenmodes, so you will need to connect the original video output separately and arrange some kind of switch between them (or use two monitors).

[pandy71]

In past this problem was solved in PC world by using hardware overlay (VGA feature connector), later it was shifted to hardware-software overlay, currently some hardware (like flicker fixer) solutions can be used but AFAIK no one offer such solution on market (PC market then even less likely on "Amiga").

So for hardware Amiga clones i can imagine module that take RGB data from Amiga chipset (sprites, dynamic changes of color registers, pixel data) and with block transfer use, send those data to the any 3D card as a RGB plane (texture?) - then with use modern hardware full (at least for not tricky video timing) compatibility can be achieved.

i know that You expect a bit different answer but... IMO chip (FPGA) that take digital data from Amiga video output and convert this to PCI/AGP/PCIex block transfer together with some code on 3D card should be doable.

[Zetr0]

@Pandy

using an FPGA as an Amiga Native Video frame buffer to chuck on a voodoo / pci gfx adapter..... nice

[alexh]

You're entering a world of expensive bespoke hardware solutions so make sure you're a true Amiga fan before starting down this road.

A Mediator 1200 TX PCI busboard (the only one currently sold) will set you back ~€188

You'll need a 4:3 LCDTV with VGA & RGB SCART input ~€100

An RGB SCART cable ~€20

A tower case of some-sort ~€150 for A1200 compatible one less if you make your own.

Probably want a PCMCIA right angle adapter €30

If you're happy to spend €400+ then we can give you all the help and advice you could ever wish for.

[whitebird]

Thanks all for your answers.

What I understand is that some (most) amiga games and demos use amiga specific resolutions/refresh rates. So those programs need for example 50Hz refresh rate to run synchronously, and it would be difficult to accomodate higher refresh rates because VBL will occur more often, so everything would go out of sync.

But to display a desktop or internet content, the timing constraint isn't crucial and this can be done through a VGA board connected through a PCI mediator.

To be able to play games and watch demos on an amiga with PCI board, we still must consider the signal coming out from the RGB connector, pass it through a PAL => VGA converter (like SCAN DOUBLEUR) which changes (X2) the timings so that it can feed a VGA display.

So if I understand well, amigas with PCI graphics have dual display, that works fine for desktop etc... but for games only the RGB is usable? Right?

For me there are two different problems with video:

1. Software pixel drawing is purely a logical concept. It fills some memory but has nothing to do with video signal timings.

2. Hardware scrollings, dynamic changes of color are video signal clocked. So it needs the native video timings. To output correctly, the VGA board, need to:

-Receive the video memory content built by amiga chips under PAL timings or
-Convert the video timings to VGA. (have an internal SCANDoubler built arround an FPGA for example)

Hope I understand well the challenge...

[whitebird]

To give you an answer alexh:

-I plan to mod a PC case for the tower, so it will cost only time.
-A VGA display + RGB screen??? (already have) or LCD with dual input??
-RGB SCART already have or can build.
-Right angle PCMCIA, need to buy
-PCI mediator need to buy


So it should be around 200€


I am not an amiga fanatic, but I really love its architecture and softwares and I think it could be interesting to have an alternative system powerfull enough for today needs.

[alexh]

Originally Posted by whitebird

amigas with PCI graphics have dual display, that works fine for desktop etc... but for games only the RGB is usable? Right?

Some games are RTG compatible but very few. So yes dual display, RTG & Native. However just like a PC with dual outputs you either need two monitors or a 2:1 VGA switcher to use a single monitor.

Originally Posted by whitebird

Convert the video timings to VGA. (have an internal SCANDoubler built arround an FPGA for example)

Or use the RGB scan doubler built into your LCDTV.

Originally Posted by whitebird

I think it could be interesting to have an alternative system powerful enough for today needs.

Think again. Even the most powerful Amiga (which you don't have) is not powerful enough to be an every day alternative system for todays needs. It runs Amiga stuff well (obviously). It runs a few great little applications ported to it well. BUT : It does not have Java, it does not have Flash, it does not really have MP3 decode or AVI decode. It does not have Word/Excel, or even a particularly good web-browser (certainly nothing which can view the majority of todays web).

If that is what you're after, get an Apple Mac (or use Hackintosh to install MacOS X onto a PC) or experiment with Linux on your PC.

If re-living the Amiga days is what you're after then upgrade and get fiddling.

[Jope]

I find that reliving the Amiga days is best with a relatively modest Amiga. No need for RTG, for example, but a lot of RAM and a network card both help. 030 or better as the CPU.

[pandy71]

Of coz switching between two videos can be made even quite easy - just synchronize V and H sync, then with use ZD at the Amiga video port switch between video (anolog) with use for example 4066 switches - this is very cheap and trivial circuit with one exception - V and H synchonization - a bit easier solution is - http://www.amazon.com/Kworld-Externa.../dp/B000MD79PE

it accept VGA analog port and some NTSC/PAL signal - then signal is converted and overlayed/switched to external LCD monitor - this solution not give very best picture from Amiga but is inexpensive and solve some problems

[whitebird]

My goal is not an alternative system that equals the power of todays PC, but to be able to run amiga software more confortably than a standard A1200.

I agree with Jope that it is better to be not too far from standard amiga to keep what makes this computer so special. Turning an amiga into a PC is without interest.

pandy71, I'm not sure I understand you well.

Is it an electronic switch to drive one display with two video sources??

Or an RGB to VGA converter?

Because switching between the source will not solve the problem of VGA timing generation. A scandoubleur first deinterleave the video by storing in a buffer, and after the image is complete displays at a higher sync frequency (31.25KHz instead of 15,625KHz)

[pandy71]

this is scaning frequency converter with embeded video switcher - it can swiitch between PC VGA and TV (S-VIDEO) sources - at the output signal compatible with modern PC displays is produced - ie it allow to watch TV freq (15.6/15.7kHz) on displays that not support anything bellow 30kHz - also video can be reized to LCD native size. - Dont expect miracles from this device but it can work as quite well working scandoubler with video switching - it allow You connect to one monitor native video from Amiga and video from Amiga graphics card.

[whitebird]

Do you have schematics for it?

[alexh]

What for? You're going to try and build your own scan doubler?

The ones out there tend to use two chips, a triple ADC to convert analog RGB into 8:8:8 digital then a video processor to scan double to 31KHz and (if necessary) scan rate convert (50Hz to 60Hz+) for LCD panels (who mainly do not sync below 56Hz).

The problems occur because most video processors do not have RGB 8:8:8 inputs. Only RGB 5:6:5 which results in lower quality (colour quantisation) on 24-bit RGB systems like an AGA Amiga.

If you're going to use the two chips above (which have been used with Atari, Amiga, Tandy and other computers) then remember to wire up the register bus as you will need to tweak the settings.

[whitebird]

Thank you for those references

You're going to try and build your own scan doubler

Today it's not a priority, but why not if necessary.

And what about amiga specific video cards? They should have a built in scandoubler or not?

Now I'm building a list of the components I need.

I already have some usefull extensions like:

-Randy rom IDE fix
-M-TEC 1230 with 28MHz 68030 and 68881.

Zetr0, I had a look at your schematics.

I understand that you show two way of connecting a PC power supply to a 1200 motherboard:

1. By soldering directly +5V, +12V and -12V on amiga supply connector
2. By soldering only -12V on the PS connector then feeding +5V and +12V through floppy drive PS connector.

Is there another way to connect -12V?

[Zetr0]

@whitebird

I shall have a look at the A1200 schamtics for you later my friend, but I do believe that around the 5 Pin connector is the only place for -12v input,

Around the filter coil there is a small header solder point that could be used - I used this on r0jaw's PPC A1200 build.

[pandy71]

-12V is on serial port (but through resistor? - low current approx 20mA capable accordingly to the specs - but it is use only by OPAMPS then low current should be enough)

[whitebird]

I shall have a look at the A1200 schamtics for you later my friend

Thanks a lot, very nice from you.