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1088XEL Alternative Mother-Board Project

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I've been hinting that this was in the works for a while now. And I figure its time to start revealing a bit of what I have been working on for the last 1-1/2 years. I call it the 1088XEL. Why? Well for one thing thanks to Lotharek's U1MB board and the on-board 64K RAM, there is a total of 1088K of usable memory. Basically the idea behind this project is to create something that is designed from the ground up to accept some of the most popular upgrades as plug-in daughter boards. Yes no more making up wire harnesses, crimping terminals, scratching your head and trying to figure out where to mount things.

 

The other goal of the project is create a very small footprint mother board. I'm talking about something in the area of 6" x 6" (15x15 centimeters). And to utilize only thru-hole components, as well as the original five A8 LSI chips (Sally, Antic, GTIA, Pokey, PIA). Actually there will be an additional Pokey on board to support Stereo Sound. If you've been following some of my other projects, then you've witnessed the nesting technique I wish to exploit when laying out this board, which is how I will get it shrunk down to such a small size without resorting to surface mount devices.

 

The first prototype will initially be created as an NTSC version board, but will provide support for an upgrade path to PAL via a future daughter board design, an oscillator change, and of course PAL Antic and GTIA chips.

 

I have taken some liberties at reducing the component count by eliminating capacitors, some support chips (through utilization of SRAM memory), and just not caring too much about RFI radiation issues. Me bad :spidey:

 

So for all intents and purposes this will still be a 'real' Atari 8-bit computer as far as the basic hardware is concerned (not an FPGA implementation).

 

Now for the big reveal (please keep in mind that these are preliminary schematics, and that the design is still in flux, so in other words there might be a few mistakes and omissions ;) )...

 

 

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- Michael

Edited by mytekcontrols
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Would it nice to make the board in m-itx size ? Then we can put the board in a m-itx case.

 

Can you give an example of that case?

 

BTW, my secondary project to this one will be a black anodized machined aluminum enclosure (not to be confused with the design I posted last year).

 

- Michael

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Have you tried to route this yet? I think you might be in for a surprise. ;) You may see your board size has to go up or your layer count go up. If your layer count goes up to keep the board size the same, you may run into issues with TH parts.

 

While you can get away with 6 and 8 mil signal traces, you're definitely going to need to use thicker traces for power and ground. And at this board size you might have to go with 8 mil size traces minimum.

 

While sometimes it's possible to do away with some caps. Caps are by and large your friend. They help provide stability.

 

A prototype thoroughly tested would tell you more of course. :)

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Do you mean mini-itx? https://en.wikipedia.org/wiki/Mini-ITX

 

It is 17x17cm, so seems possible. Cases are plentiful, some of them really, really nice.

 

That will definitely be a good target to shoot for (thanks to both people that suggested this). Now I'll have to go see what some of those cases look like, and study this in more detail.

 

 

Have you tried to route this yet? I think you might be in for a surprise. ;) You may see your board size has to go up or your layer count go up. If your layer count goes up to keep the board size the same, you may run into issues with TH parts.

 

While you can get away with 6 and 8 mil signal traces, you're definitely going to need to use thicker traces for power and ground. And at this board size you might have to go with 8 mil size traces minimum.

 

While sometimes it's possible to do away with some caps. Caps are by and large your friend. They help provide stability.

 

A prototype thoroughly tested would tell you more of course. :)

This will be a 4-Layer board, so power and ground get their own layers (power planes). I found a place in China that is very reasonable for doing this, especially where larger boards are concerned. And they'll do as few as 5 boards in a run, which is good, since it likely will take at least two or three runs to get this right.

 

I haven't finished the power supply aspect yet, so there will be a few more caps, and possibly a few inductors added, but nothing major since I'll be going with an off board switcher (thinking cell phone/iPad charger).

 

The caps and inductors that I have left out, are associated with the external SIO and joystick inputs. I don't think these will be missed, and in some cases (think SIO) probably even beneficial. As for stability, which is a good point, you'll notice that every single IC still has a decoupling capacitor associated with it in order to squelch gate switching transients from getting into the power bus. Combined with the sandwiched power planes, this should yield a very stable design (or at least I hope so -- fingers crossed).

 

Haven't begun the board layout in earnest yet, although I have been doing some initial IC placement that suggests the small footprint should work. Of course using 4-Layers will make this easier, since I don't have to route power connections, nor will they get in the way of logic traces. But the layout is on hold until such time that the design gets finalized and gets past the preliminary stage where it's at now. And I guarantee there will be a few changes required before it is final ;) .

 

- Michael

Edited by mytekcontrols
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Wow very interested in this project, I have quite a few spare Atari's and nearly all of the mod/s upgrades. I would love to help out anyway I can...

 

Best Regards

Robert

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Wow very interested in this project, I have quite a few spare Atari's and nearly all of the mod/s upgrades. I would love to help out anyway I can...

 

Best Regards

Robert

 

Thanks Robert :) Thanks for the offer to help, but as far as parts are concerned, I'm pretty well stocked up. And I'm also within a 2 hours drive of B&C and Bob Woolley's house, so if I don't have it, they surely do. Also expecting delivery on two more U1MB any day now. Speaking of which, I will have to mod those, changing from right-angle to vertical pin headers since those will need to plug straight into my board. If this project succeeds I will contact Lotharek and see if it is possible to have him do a run of boards with the same style headers.

 

- Michael

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I found a good document on the Mini-ITX Form factor here. This will be good bathroom study material ;)

 

- Michael

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This is an awesome design concept that is definitely needed, and more importantly wanted. Thanks Michael for your hard work, although it seems your rather enjoying the 8bit adventure.

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I agree, it should fit an existing case. 800/1200/130 something. Like the c64 reloaded board...

 

Sorry not going to happen on my watch, or should I say... not by me :) . However since all the design files for this project will be released into the public domain when I have working boards, anyone is free to jump in and create an alternative from my design. And I encourage them to do so.

 

BTW, here was the inspiration for my project...

 

post-30371-0-59611100-1311577466.jpg

 

Link to Compact 5200 project

 

- Michael

Edited by mytekcontrols
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too bad, they cant keep the reloaded in stock. the c64 scene has exploded the last few years, too bad Atari hasn't really.

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I hope you don;t do what that guy did. Post some really cool work then not release anything and disappear....

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I hope you don;t do what that guy did. Post some really cool work then not release anything and disappear....

 

Don't worry, you guys are stuck with me. Although as I get older I and have seen a few friends leave this planet, and it does make me wonder :ponder: But enough of that :-D No I have no plans to disappear anytime soon. And if you check out my website link, you'll see that I already have several released projects under my belt.

 

It is unfortunate that the Compact 5200 guy disappeared. I really liked what he did :thumbsup:

 

- Michael

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Opps... already found a small error in labeling. On the last schematic 'MISC CONN' , pin 13 of the U1MB header is labeled as RSEL. In actuality it is the /MPD signal. This was left over from an early design which had been based on the XEGS. I'm pretty sure that this won't be the only mistake I've made :(

 

- Michael

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At least make it small enough to jam into an existing atari case. Think its kinda silly putting it into a PC case... I'd just use a damn PC to emulate at that point.

 

Now that I know about the Mini-ITX spec, I'll likely follow that form factor, so that'll make the footprint 17 x 17 centimeters. Are you calling me silly to consider that? :grin: Actually my goal is to still do a custom enclosure for it, so that I can call the shots where connectors will be placed, and also do some nice graphics on the panels. Judging by some of the prices for the real fancy ITX cases, I think there are ways to get a custom enclosure to be competitive. Besides who wants to drill holes and such if they don't have to. Using a form factor that works for Mini-ITX is logical since it gives the user a multitude of choices.

 

Now as to you putting this into a stock Atari enclosure, please keep in mind that it isn't going to have the support circuitry or connectors to plug in the original keyboard. This is all PS2 baby :)

 

- Michael

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Hi Michael-

 

Presume you will post a "sketch" or rendering and a list of what mods you have planned on being able to attach (when available)?

 

Excellent project, BTW!

 

-Larry

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Now that I know about the Mini-ITX spec, I'll likely follow that form factor, so that'll make the footprint 17 x 17 centimeters. Are you calling me silly to consider that? :grin: Actually my goal is to still do a custom enclosure for it, so that I can call the shots where connectors will be placed, and also do some nice graphics on the panels. Judging by some of the prices for the real fancy ITX cases, I think there are ways to get a custom enclosure to be competitive. Besides who wants to drill holes and such if they don't have to. Using a form factor that works for Mini-ITX is logical since it gives the user a multitude of choices.

 

Now as to you putting this into a stock Atari enclosure, please keep in mind that it isn't going to have the support circuitry or connectors to plug in the original keyboard. This is all PS2 baby :)

 

- Michael

 

My apologies in calling it silly.

I personally would not be interested in something like this but it sounds like a cool project.

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I Don't want to get too far ahead of you, but how much of the board will be socketed? Reason I ask is because I have a penchant for adding a second 74ls138 to my motherboards and it is convenient to have them socketed. A bare board or fully socketed main board would be perfect. Also, on my list of to do but never got around to doing is switching to SRAM so refresh isn't necessary and bank switching could just be done simple like a 74LS374<?>. Certainly the 64k RAM you use is a step in the right direction. I'm also not against 44 pin ICs at some point since there are a lot of adapters that can be used i.e. 44 pin ROM that have multiple OS and BASIC installed. Good work as is of course. As a community we are better off with whatever you do.

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Hi Michael-

 

Presume you will post a "sketch" or rendering and a list of what mods you have planned on being able to attach (when available)?

 

Excellent project, BTW!

 

-Larry

 

Hi Larry :)

 

I haven't even begun the board layout other than just some playing around with pushing IC footprints around on paper. Since I really don't want to have to rip up a bunch of traces and re-route, I'm really holding off on that aspect until I have good certainty that the schematics are accurate. So for instance, I have some SRAM coming and when it arrives I'll be wiring it into my XEGS in place of FREDDIE and the 64K x 4 DRAMS just to be certain that all is well with that approach (although Bob Woolley and I have been conversing on the subject, and he helped me to integrate this aspect so it should work). I have an XEGS that is fully socketed and has a bunch of upgrades attached, so it makes for a good test bed.

 

As for mods that can be attached. Several of the usual ones are already integrated (U1MB, UAV, TK-II PS2 Keyboard, PS2 Mouse, SIO2PC-USB). I'll also be trying to maintain compatibility with the new GTIA in CPLD RGB/Component Video board (got two on the order list). Probably some of the other stuff such as Rapidus and VBXE will not be easy fit. Not impossible, but there is only so much room to place things in a 17 x 17 cm footprint, so it would be a challenge. Of course all of the LSI chips will be socketed, as well as the Microchip PIC MCU's, but much of the glue logic will be soldered in, since it will be mounted underneath the LSI chips in many cases and there just isn't the headroom.

 

Don't think I'll do any renderings, but when the PCB starts to come together I'll be posting captures from the layout editor as I go.

 

 

 

My apologies in calling it silly.

I personally would not be interested in something like this but it sounds like a cool project.

 

No offense taken. I was just yanking your tail :grin:

 

 

I Don't want to get too far ahead of you, but how much of the board will be socketed? Reason I ask is because I have a penchant for adding a second 74ls138 to my motherboards and it is convenient to have them socketed. A bare board or fully socketed main board would be perfect. Also, on my list of to do but never got around to doing is switching to SRAM so refresh isn't necessary and bank switching could just be done simple like a 74LS374<?>. Certainly the 64k RAM you use is a step in the right direction. I'm also not against 44 pin ICs at some point since there are a lot of adapters that can be used i.e. 44 pin ROM that have multiple OS and BASIC installed. Good work as is of course. As a community we are better off with whatever you do.

 

I'll try to keep the HCT138 in a socket and accesable, since it has some valuable signals on it. Thanks for pointing that out :)

 

If it wasn't for the requirement by the U1MB to still have 64K of base ram, I wouldn't have any ram on board, since it acts as my ram upgrade (and is a requirement that it exists for my board -- notice that there isn't either an MMU or OS ROM socket). So is 1088K enough ram for your uses?

 

- Michael

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