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1088XEL Alternative Mother-Board Project

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In the interest of keeping things 100% backward compatible, what about access to the Pokey keyboard lines so an Atari keyboard could be used.

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Have you thought about connecting the second pokey's ~irq line? It would be nice to have three more timers (or two extra 16-bit timers).

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In the interest of keeping things 100% backward compatible, what about access to the Pokey keyboard lines so an Atari keyboard could be used.

 

I have no interest in doing that. I could see supporting the stock keyboard if my aim was all about recreating the look and feel of the A8, but it isn't. This project is focused on creating a motherboard that can be easily re-cased in a multitude of off-the-shelf enclosures (i.e., Mini-ITX or ATX), while providing a standardized plug'n'play interface for many of the currently manufactured hardware upgrades (Rapidus, VBXE, Sophia, UAV, U1MB), and integrating some of the others (Stereo Pokey's, SIO2PC-USB, Mouse). Supporting the stock keyboard in this scheme would require a custom enclosure for it and an unwieldy flat cable to connect it. PS2 makes so much more sense for what this is about. Sorry :(

 

 

Have you thought about connecting the second pokey's ~irq line? It would be nice to have three more timers (or two extra 16-bit timers).

 

Wouldn't that cause a problem for an OS that is unaware of this, such as an unintentional interrupt occurring from the 2nd Pokey?

 

- Michael

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Wouldn't that cause a problem for an OS that is unaware of this, such as an unintentional interrupt occurring from the 2nd Pokey?

 

I don't think the second Pokey will start firing interrupts when it is just powered on and not initialized. But if you want to be safe, you could perhaps hide it behind a jumper?

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I have no interest in doing that. I could see supporting the stock keyboard if my aim was all about recreating the look and feel of the A8, but it isn't. This project is focused on creating a motherboard that can be easily re-cased in a multitude of off-the-shelf enclosures (i.e., Mini-ITX or ATX), while providing a standardized plug'n'play interface for many of the currently manufactured hardware upgrades (Rapidus, VBXE, Sophia, UAV, U1MB), and integrating some of the others (Stereo Pokey's, SIO2PC-USB, Mouse). Supporting the stock keyboard in this scheme would require a custom enclosure for it and an unwieldy flat cable to connect it. PS2 makes so much more sense for what this is about. Sorry :(

 

 

 

Wouldn't that cause a problem for an OS that is unaware of this, such as an unintentional interrupt occurring from the 2nd Pokey?

 

- Michael

A simple male pin header, that is. I have an empty 800XL case with keyboard. A good place for this new motherboard...

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A simple male pin header, that is. I have an empty 800XL case with keyboard. A good place for this new motherboard...

 

That simple pin header would require 12 connections if you also want the Console and Reset keys included, which I imagine you probably would. And you'll also need the two 4051 MUX chips for the key scan circuit as well. The only exceptions to this would be an XEGS keyboard (which is crap), or a 1200XL keyboard, both of which have the key scan circuit inclusive. By the time I finish adding all of the 'essential' parts, I seriously doubt I would have the room for any of this other stuff. But if you really want to interface this to the stock 800XL keyboard, you could always pull the TK-II chip and interface to a key scan circuit through its socket :)

 

- Michael

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I saw that already, as well as another much longer topic pretty much discussing a similar thing. Candle's idea of making something to fit inside a disk drive case was pretty cool, but at the same time limited to the availability of that case. Also notice that he too was thinking of using alternative connectors for SIO and PBI. And obviously he also had an advantage because of owning the rights to things like the U1MB and VBXE, thereby allowing him to integrate that directly into the motherboard. But also notice the date of the last posting ;)

 

This discussion of a new motherboard has been started many times over the years. But it never seems to go anywhere. Now could that be attributable to people wanting to add anything and everything to the design :ponder: :? :grin:

 

By far I think I have shown far more progress in my attempt at a new mobo, or at least what has been disclosed thus far. Candle says he's got his PCB design sitting on his Cam Station, but of course that was 6 years ago. Hopefully he didn't erase it ;)

 

On a side note... I think it was a fantastic idea that was proposed of making my mobo be patterned after a Mini-ITX form factor, because it will allow me (or anyone) to utilize a sexy looking case like this...

91Z8JF-YvPL._SL1500_.jpg

Of course that's overkill, but at $85 and free shipping it would be impossible to match that with a DIY case. And of course there is lots of room for whatever ???

 

- Michael

Edited by mytekcontrols
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Michael - I agree that feature creep has delayed the progress of many great ideas and in a lot of cases stopped them dead in their tracks. Thanks for your hard work and the journey of sharing your design development with us!

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Have you thought about connecting the second pokey's ~irq line? It would be nice to have three more timers (or two extra 16-bit timers).

 

Ok I tried connecting the 2nd Pokey's IRQ to the 1st one and have run a couple of applications and games with no ill effects. Before I implement this in my design, can anyone think of a problem and/or a test to be certain that this is ok?

 

I'd rather not have to put in a removable jumper unless it's necessary.

 

- Michael

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Having both Pokey's sharing an IRQ still hasn't caused any problems as far as I can see, so at least for now I have updated my design. And because of a lot of fine tuning, and the decision to include the PAL clock generator on-board, there are multiple changes (too many to list).

 

I still consider this a work in process, but that won't be the case for too much longer. Updated 1088XEL Schematic: 1088XEL_V1_X_2-2-2017_schema.pdf

 

When things look to be totally locked in, I'll generate the component ID's (Rxx, Cxx, Qxx, Uxx, ect), and give the document a 1.0 revision level.

 

- Michael

 

Edited by mytekcontrols
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Leaving the second IRQ line connected caused problems with the old Mega-HZ stereo Pokey boards and the solution was to lift the IRQ pin on the second Pokey or cut the trace.

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Leaving the second IRQ line connected caused problems with the old Mega-HZ stereo Pokey boards and the solution was to lift the IRQ pin on the second Pokey or cut the trace.

 

Could you elaborate on what problems occurred? I tried searching for it, but couldn't find anything.

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Could you elaborate on what problems occurred? I tried searching for it, but couldn't find anything.

 

At least one game Yoomp! will hang if the 2nd Pokey's IRQ is connected. Here is where it was reported as a problem for the Mega-HZ stereo board.

 

I also confirmed this on my own setup this morning (jumpered IRQ's together on TK-II Stereo Board). I wonder what Yoomp! is doing that causes this and why :?

 

- Michael

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I suspect it writes a non-zero value to $D21E (IRQEN on second pokey). But the question remains, why?

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I suspect it writes a non-zero value to $D21E (IRQEN on second pokey). But the question remains, why?

Most likely because of sloppy programming. I haven't looked at it yet.

The simple fix would be to patch the offending software, or use one of the U1M's switchable output pins (if there are any left) to dis/en able the IRQ.

If all else fails, a motherboard jumper would do the trick for a very low cost.

 

My .02

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Hi

I just wonder - is this going to be stand alone solution, or just a plug in base board? If the First one, then where is rom chip? It seems that u1mb is a must for this to run

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If anyone wishes to see Rapidus and VBXE compatibility I still need the following dimensional data for each board...

 

VBXE Top View (XE Model Version 2.x)

5I7bWjt.png

 

Rapidus Top View (XE Model)

 

d9EcWDK.png

 

Thanks to anyone that can supply this information :)

 

- Michael

Man - I am really sorry about this. Not only am I a week behind in getting you the measurements, when I finally dug out my VBXE, it seems it is not the version you need. I am attaching a picture to see if any of this can assist you.

 

post-650-0-63716200-1486340622_thumb.jpg

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Most likely because of sloppy programming. I haven't looked at it yet.

The simple fix would be to patch the offending software, or use one of the U1M's switchable output pins (if there are any left) to dis/en able the IRQ.

If all else fails, a motherboard jumper would do the trick for a very low cost.

 

My .02

 

Yeah I like your suggestion about using one of the U1MB control lines as a 2nd IRQ disable :)

 

 

Hi

I just wonder - is this going to be stand alone solution, or just a plug in base board? If the First one, then where is rom chip? It seems that u1mb is a must for this to run

 

Yes the U1MB is an absolute requirement, same as the UAV board for video output. Your creation is the must have device for the A8, so I figured why not just go with it as part of the design, only make it easier to install with absolutely no soldering required. Well that assumes that we can talk Lotharek into making a run of these with vertical headers (the idea is to have it pug straight into my board, no ribbon cables or crimp terminals required.

 

 

Man - I am really sorry about this. Not only am I a week behind in getting you the measurements, when I finally dug out my VBXE, it seems it is not the version you need. I am attaching a picture to see if any of this can assist you.

 

attachicon.gifVBXE2_1.jpg

 

That looks like the same adapter mirrored to stick out of the opposite end.

 

Thanks for at least trying :)

 

- Michael

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The U1MB was designed to have vertical headers anyway and I wish boxed IDC housings would be permanently reinstated. I'm not sure why open right-angle headers were one day deemed a great idea.

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To shave some pennies i suppose, you know How It looked when lotharek took over - no emulation headers, no pins, just solder it for good - not the way i'n doing things, but at least It was available and still is

I can't say v2 wilk be footprint compatible with v1 - i might try, but i wont resort to bga just to accomplish that.

Also - why tht components only? For ram chip It seems like shooting in your own feet

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To shave some pennies i suppose, you know How It looked when lotharek took over - no emulation headers, no pins, just solder it for good - not the way i'n doing things, but at least It was available and still is

I can't say v2 wilk be footprint compatible with v1 - i might try, but i wont resort to bga just to accomplish that.

Also - why tht components only? For ram chip It seems like shooting in your own feet

OK I'll bite, how am I shooting my own feet? Perhaps you are referring to the obsolete nature of the ram chip I picked. This was done since I wanted a thru-hole 64k x 8 SRAM device. However just like many obsolete type of things (i.e., Atari) it is available through eBay and at a very reasonable price. Or perhaps you are wondering why in the world would I not be using SMD components? That one is simple, a lot of us A8'ers are getting a bit long in the tooth (as in older) and our eyes and dexterity are not what they used to be, making it difficult if not impossible to work with such small components. And please do keep in mind that this project is just something I 'feel' like doing and is not intended to be a commercial release, so as such it might not make sense from that point of view. However like all things that I have done related to the various A8 upgrade projects, this design will also be released for DIY persons to build if they so desire.

 

The two main reasons I have been posting about this project, is one to share my journey, and secondly to benefit from suggestions that fall inline with my ultimate vision of what this project is about for me. To that end the idea has been evolving, and appears to be destined for a positive outcome. If others agree, so much the better. If not, well then call me crazy.

 

- Michael

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I can see that all your designs are THT only, and this is ok - but as RAM chip goes - i can belive 32k DIP SRAM chips are dozen for a dime, since this is popular size to be found in old 486 motherboards as cache ram, but 64k is something rare i think - i have none, altough i have plenty of 32k ones (in 300 mil wide dip package that is)

sure, atari is obsolete so obsoleteness shouldn't be brought to the discussion at all - some time ago was 1400xl motherboard to populate, and people here managed to get it assembled regardless of how odd/hard to find components were there

If you really want to stay with THT and it should be at least available for next few years to purchase i would go with 600mil wide DIP32 package and 128k SRAM chip from Alliance - they are here to provide RAM solutions that are considered obsolete for most other manufacturers, but leaving it as is - 300 mil wide might just end with another folk making an adapter for whatever standard ram package will be

I don't think that design that requires adapters just to populate its socket is the way to go

 

also - why using 2 PBI connectors? If anyone wants pbi device inside, then it will be connected using a ribbon cable, and to minimalize lenght of that cable it would be better to put second device on the same cable (daisychained) instead of having separate cable running to it

1.7mhz doesn't seem like challange right now, but remember that these PBI devices often failed from one reason or another - NMOS drive capability is really poor

 

i've noticed that you have RAM chip select connected to PHI2 line - there is considerable delay in data out to chip select time, and i wouldn't go that way, but if you have your math done here, and feel line on the safe side - it's up to you

i would rather use that chip select as extsel/casinhibit and use proper oe and we strobes

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Hi candle,

 

That's a good point about the RAM chip, but I've seen it done both ways (deselecting /OE on write - and - tieing it directly to ground as I have done). The important thing as always is to only write when PHi2 is high.

 

That's funny, I have lots of 64K x 8 chips laying around, and no 32K x 8 which is the opposite of you (I have ten 64K x 8 chips on hand, so that means I can build 10 boards if I really wanted to --- NOT). You can buy 10 UM61512A's (64K x 8 SRAM) for $1.47 each (link) or just one for $2.16 (link). Not a dime, but certainly not a deal breaker either. So obviously not a big issue, and it does provide for a smaller footprint on my board which will become quite important as I progress into the lay-out.

 

Two PBI's :? Just because. No other reason than that. Well not that anyone would likely agree on that is ;)

 

It's nice to see you posting stuff again. Seemed like you were quiet for some time, although maybe it was because I wasn't reading the same topics as you were visiting :ponder:

 

- Michael

Edited by mytekcontrols

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Regarding the 0.3" vs 0.6" wide RAM chips, if there is room on the board what about putting pads in for both(the 0.3" socket footprint inside the 0.6" socket footprint). Either socket can then be installed as desired.

 

I know you already have the part Michael, but it would save someone else in the future who can't get the .3" wide part from needing an adapter(or having to modify the layout of the PCB before having them made).

Edited by BillC
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