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PostPosted: Thu Sep 01, 2016 8:08 am 
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I don't have the knowledge to make such a project but I always had the interest to do so. If it already been talked in another thread then I apologize in advance.

What I would like to know is, let's say someone would try to make a game console with parts that were common in older generation consoles. By older parts I don't means to salvage from older hardware but use the same hardware from 20~30 years ago since I like those old CPU or other video/sound hardware.

What would be the challenge of doing such a project? For example, are parts still available? Now that most people only use LCD, would it be possible to adapt the signal for new television sets? For video, does chips still exist or you have to make them with some programmable chip (I forgot the name of it but it was used to make some emulated nes hardware).

This is just all "in theory" but those things fascinate me and want to learn more about what is possible and the limitation of what can be done today.


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PostPosted: Thu Sep 01, 2016 8:43 am 
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If you do find new-old-stock or pulled TMS9918, SN76489, and Z80 chips, you can pair them with off-the-shelf 7400 parts for address decoding and off-the-shelf 62256 SRAMs to make your own ColecoVision or SG-1000.

Most LCDs should still be able to display analog composite or component video. As a last resort, you can modulate analog composite video to an RF signal because TVs still have to decode that (or they can only be legally called monitors, not TVs).

The programmable chip is called an FPGA. The low-end programmable chip is called a CPLD; you might be able to make your own sound chip out of one of those. Video is a lot more complex because although the Apple II video circuit is elegantly simple, gamers demand sprites at 60 fps, and a dumb frame buffer like the Apple II's has trouble delivering that.

So now your question has been reduced to "Are there reliable sources for new-old-stock retro video and audio chips?"


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PostPosted: Thu Sep 01, 2016 8:52 am 
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This is certainly possible, but most machines had custom video chips, so you'd most likely have to harvest them. But AFAIK, it should be possible to make interesting combinations, like controlling an NES PPU using a Z80. FPGAs are the programmable chips your talking about, and depending on their capacity you can even implement entire machines in them, meaning you can create entirely new designs inspired by old machines, but with video, audio and CPU created by you from the ground up. Or you can clone existing parts, depending on what your goal is.

As for connecting to newer TVs, some old code chips output signals more friendly than composite video, such as the SMS VDP, which outputs RGB, that you could possibly convert to HDMI and get good results.

The NES PPU outputs composite video, which direct scale well to HDMI, but it also has a digital output that with some trickery can be (and has been!) used to generate pixel-perfect pictures for HDTVs.


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PostPosted: Thu Sep 01, 2016 8:57 am 
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Did the Playchoice 10 use Z80+PPU?

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PostPosted: Thu Sep 01, 2016 9:03 am 
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tepples wrote:
If you do find new-old-stock or pulled TMS9918, SN76489, and Z80 chips, you can pair them with off-the-shelf 7400 parts for address decoding and off-the-shelf 62256 SRAMs to make your own ColecoVision or SG-1000.

Or an MSX, but I guess that's a bit more complex than the two you mentioned.

The TMS9918 is a good example of an off-the-shelf video chip, but making good graphics on it can be a challenge, much more so than on the NES, IMO. It's definitely possible, but the lack of hardware scrolling and the poor sprite capabilities (1 color + transparency, maximum of 4 16x16-pixel sprites per scanline, no priority control against the background) greatly limit the possibilities of what you can do.


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PostPosted: Thu Sep 01, 2016 10:41 am 
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Dwedit wrote:
Did the Playchoice 10 use Z80+PPU?
No, it used a discrete logic tilemap display instead of an ordinary PPU, with a giant array of EPROMs for both the tile definitions and palette. (If you look at http://nesdev.com/Playchoice.pdf , it's basically the entirety of sheet 2. The "nametable" is the RAM 8R (on sheet 1), the rasterizer is 6H through 6L plus 5M and 5Q, the tile definitions are in the 8Kbyte EPROMs 8K through 8P, the palette in the 256x4 EPROMs 6D through 6F.)



Anyway, one should still be able to build an all-new-parts ZX81, but it might count as a bit too retro.


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PostPosted: Thu Sep 01, 2016 4:18 pm 
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Similar to the ZX81 idea, this was an actual (throwaway) arcade board that uses a surprisingly low number of logic ICs to generate bitmapped graphics: http://www.chrismcovell.com/dottorikun.html

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PostPosted: Thu Sep 01, 2016 4:36 pm 
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You might want to look into the chips that are used in the plug and play consoles. They are not 6502 or Z80 by any means, they are some other 16-bit architecture, but they are cheap and mass produced and still being used.
Who was using them besides Jungletac?

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PostPosted: Thu Sep 01, 2016 5:58 pm 
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@Tepples

So I guess our recent television that we bought after the switch to digital may be called a monitor instead. The coaxial doesn't react to the old famicom rf but the new famicom with rca jacks works well. As for pulled chips, it would be preferable new ones when possible but I guess from your comment this means graphical chips of that style are no longer available.

@Tokumaru & Tepples

FPGA is the terms I was looking for but I was too tired that I couldn't remember it. Thanks.

If could build something, I would use either a 6502 or z80 since they seems simpler than "newer" chips like the motorola 68000. I searched briefly and there seems to be some solution for the 6502/z80 but they are talking about SOC so I'm deducing that the chip is not in it's original package.

As for video, I guess you could invent your own tile based system (I would want to avoid a frame buffer for a low spec system since I guess it would hinder scrolling) but that would increase the complexity and I would prefer off the shelf parts when possible.

As for sound, something similar to the nes or sms would be fine.

Let say you would have all those chips, is it possible to prototype such a system on a breadboard?

Now if I reverse my stance and say I would decide to develop a system with FPGA, would I need one FPGA per subsystem? How more complex would it be compared to off the shelf parts?


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PostPosted: Thu Sep 01, 2016 7:21 pm 
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That probably depends on the details of your particular country's transition to digital broadcast. In the USA at least, TVs need to receive both analog and digital RF signals because low power stations were allowed to continue to transmit analog. In addition, "Digital Transport Adapters" (compact cable TV decoders without video on demand) used on Comcast have only an analog RF out.

As far as I can tell, you could put your ghetto ColecoVision parts on a breadboard.

You could fit a whole NES in an FPGA, including 6502, APU, PPU, and mappers. Kev has done it.


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PostPosted: Thu Sep 01, 2016 7:34 pm 
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Banshaku wrote:
Now if I reverse my stance and say I would decide to develop a system with FPGA, would I need one FPGA per subsystem?

I won't pretend I'm an FPGA expert, but I've seen people build entire systems on a single FPGA. I guess it depends on how complex the system is and how powerful the FPGA is. I'm pretty sure I've heard of people recreating even an SNES using a single FPGA.

This was the idea behind the infamous Retro VGS / Coleco Chameleon: a powerful FPGA would be configured to simulate a different system depending on the game being played.

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How more complex would it be compared to off the shelf parts?

I'd say ridiculously more complex it you're trying to recreate existing chips accurately, but if you're creating your own custom stuff, without having to adhere to existing specs, I guess it wouldn't be particularly hard if you keep the design simple (more 8-bit than 16-bit), but it would still be more complex than using off-the-shelf parts. Creating your own CPU and video architecture sounds like fun, though.


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PostPosted: Thu Sep 01, 2016 9:23 pm 
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@Tepples

In Japan we went to full digital in 2011/04 but the regions affected by the earthquake got a delay to help receive information for people that didn't buy a televion that support digital yet. It could be my rf box is bad but I 'm sure it was working. I will try it someday on a older tv once I have access to one.

@Tokumaru

I'm sure it must be great to reproduce a complete architecture on a FPGA but since I don't know verilog or how to use the FPGA properly it feels that it would be quite a steep learning curve. If I want to learn architecture, programming an emulator on a pc would be quite interesting too. If I do start a project like that, I want to go off the shelf first for the learning experience before going deeper. Now I now that 1 FPGA can cover all sub systems.


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PostPosted: Thu Sep 01, 2016 10:54 pm 
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If you look on the forums at http://6502.org/ you'll find quite a few examples of home-built computers and discussion about what parts to use. But if we consider what makes a console distinct from a computer, it's mostly going to be the focus on graphics and sound.

For graphics, pretty much the only options are going to be using obsolete parts (maybe Yamaha V9958 or V9990 if you want to go beyond the Colecovision/MSX level), make your own in an FPGA (or LOTS of TTL logic, you can look at early 80s arcade schematics for examples), or settle for something relatively weak (like the Propeller chip by Parallax can output video, but it's definitely not a video processor, more like manually controlled like the 2600's TIA).

Pretty much the same deal with sound, make your own, or use obsolete parts. I kinda like the YM2151 myself, but with that you need a special Yamaha DAC, and those chips are power hogs and run really hot. Maybe there's a more modern (but still certainly obsolete) alternative. Pretty much the only standard sound chip you can buy I think is going to be a standard audio DAC with i2s interface, and you can buy pretty good MCUs that can interface with those (this is the route my Squeedo synth is ultimately taking). Or if you can run your 6502 or Z80 fast enough, you can just synthesize the audio with your main CPU and use a simpler kind of DAC. Or I suppose if you wanted to go modular, just include a UART capable of MIDI-OUT and connect it to your favorite MIDI device.

Thing is with modern parts, there's pretty much only 2 ways that it goes. You've got high-end stuff (which is still pretty cheap considering it's capabilities, look at the CHIP for example https://getchip.com/), but it's going to be an SoC (system-on a chip). The manual for one of these things (assuming you could actually get ahold of it) would probably be some 5,000 page monstrosity. Then there is the lower end simpler stuff, like you'd see in toys and TV-game type things. Those aren't going to be usable chips, just silicon under an epoxy blob, and the supplier is not even going to talk to you unless you want to buy millions of them.

I'm sure there are other options other than those, I'm not expert, just an enthusiast. :)


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PostPosted: Fri Sep 02, 2016 9:40 am 
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@Memblers

So it seems the consensus is the cpu will be fine but video/audio will be an issue.

I should first try to define my target before starting anything. As for my case, I'm not an enthusiast, just enthusiastic about this subject :) I really want to learn about it someday.

These days the programming I do at work is quite dull (IOT related, MQTT messaging/aggregation of streaming, basically the testing of a pipeline, making vm for that etc) that I need to find something to bring back the motivation. Either that or restart to work on some nes homebrew like I did 8 years ago but do something original instead of trying to reproduce something that already exist.

Thank you everyone for your comments, I really appreciate it. If there is other things that I should be careful I'm all ears.


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PostPosted: Fri Sep 02, 2016 10:04 am 
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I'm of the opinion that programming software is more rewarding than creating hardware that needs new software, specially if your time to work on such projects is limited. Creating new hardware will be a lot of work by itself, but you'll hardly see any results until you create the software to run on it, so you might just as well code a game for an existing machine and get results faster.

It really depends on your goals, I guess. Creating a new computer/console does sound like fun, I too would like to try that some time, but I imagine I'd be somewhat frustrated for not having any cool games to showcase my newly created machine.


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