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7800 Expansion Module


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#1 Curt Vendel OFFLINE  

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Posted Fri Jun 12, 2009 12:41 AM

I am going back to tackling the 13bit MCU used in the 7800 computer keyboard in August. In the meantime, I am considering a small 250-300 pc run of the Piggyback CPU module design originally proposed for the Atari 7800...

However, instead of a computer CPU this would be an expansion module, so far I will commit to the design the following features:

1. Built in High Score Cartridge capability (thanks to Pacmanplus and others, more and more games are now HSC enabled making this a more valuable feature to the system as a whole)
2. A 16K RAM upgrade
3. A Pokey Chip

The module is fairly roomy relatively speaking and there would be room for say an extra eprom and supporting discrete logic to have a built in game as well which would be over ridden when a cartridge was inserted a top of it.

Without going for pie in the sky wish lists and features, besides whats included above, is there anything else that should be a must have feature added to this Expansion Module? (Remember, it is limited to the data/address lines, Clk2, R/W lines, Ext Audio and IRQ lines... there is no video or anything else, so don't ask for something like enhanced video or some such nonsense that just can't be done through a cartridge port enhancement.



Curt

#2 gdement OFFLINE  

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Posted Fri Jun 12, 2009 1:04 AM

The RAM/Pokey functions make it similar to what the XBoard does, so some compatibility with that would be useful.
Will it interface at the same addresses as the XBoard, and provide some easy way to detect the ram size (16kb instead of 128kb)?

Detecting ram size probably isn't a big deal though - you could just try storing different values in each XBoard bank and determine that the extra banks don't work.


I know a lot of people might not care about the XBoard and consider it "dead", but it does exist, a couple homebrew games support it, and if these devices perform similar functions there's no need for them to have incompatible interfaces.

Edited by gdement, Fri Jun 12, 2009 1:10 AM.


#3 Mord OFFLINE  

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Posted Fri Jun 12, 2009 1:37 AM

Is it a safe bet that this won't be ready until after christmas? I know I'm going to be wanting one, but wondering how long I'll have to save up for it. ;)


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#4 Gorf OFFLINE  

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Posted Fri Jun 12, 2009 6:23 AM

I am going back to tackling the 13bit MCU used in the 7800 computer keyboard in August. In the meantime, I am considering a small 250-300 pc run of the Piggyback CPU module design originally proposed for the Atari 7800...

However, instead of a computer CPU this would be an expansion module, so far I will commit to the design the following features:

1. Built in High Score Cartridge capability (thanks to Pacmanplus and others, more and more games are now HSC enabled making this a more valuable feature to the system as a whole)
2. A 16K RAM upgrade
3. A Pokey Chip

The module is fairly roomy relatively speaking and there would be room for say an extra eprom and supporting discrete logic to have a built in game as well which would be over ridden when a cartridge was inserted a top of it.

Without going for pie in the sky wish lists and features, besides whats included above, is there anything else that should be a must have feature added to this Expansion Module? (Remember, it is limited to the data/address lines, Clk2, R/W lines, Ext Audio and IRQ lines... there is no video or anything else, so don't ask for something like enhanced video or some such nonsense that just can't be done through a cartridge port enhancement.



Curt


My question to you is will that extra RAM be accessable to Maria? I am assuming yes, but if not, you must reconsider and allow this.
It will allow me to do the games I really want to do on the 7800...it would certainly make that Zaxxon clone a lot easier to deal with. ;)


Hope you are doing well btw!

Edited by Gorf, Fri Jun 12, 2009 6:27 AM.


#5 Gorf OFFLINE  

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Posted Fri Jun 12, 2009 6:26 AM

The RAM/Pokey functions make it similar to what the XBoard does, so some compatibility with that would be useful.
Will it interface at the same addresses as the XBoard, and provide some easy way to detect the ram size (16kb instead of 128kb)?

Detecting ram size probably isn't a big deal though - you could just try storing different values in each XBoard bank and determine that the extra banks don't work.


I know a lot of people might not care about the XBoard and consider it "dead", but it does exist, a couple homebrew games support it, and if these devices perform similar functions there's no need for them to have incompatible interfaces.


If I remember correctly, the Xboard does not allow Maria access to the XBoard RAM as RAM but only ROM?
That would be one feature I'd hope to see changed if Curt tries to maintain compatibility with XBoard. My
guess is it would be possible to allow that RAM to act as both and still remain compatible....or do I completely
misunderstand the purpose of the RAM in the XBoard?

#6 Gorf OFFLINE  

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Posted Fri Jun 12, 2009 6:27 AM

Is it a safe bet that this won't be ready until after christmas? I know I'm going to be wanting one, but wondering how long I'll have to save up for it. ;)


--
Mord

Hey, at least you have pleny of time. ;)

Edited by Gorf, Fri Jun 12, 2009 6:27 AM.


#7 carmel_andrews OFFLINE  

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Posted Fri Jun 12, 2009 7:25 AM

the fact that the expansion module is going to be supported in this way must indicate that enough 7800's are out there that had the expansion port buss internally (even if tramiels atari redesigned the case externally for the module to be sealed off)

#8 Bakasama OFFLINE  

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Posted Fri Jun 12, 2009 8:05 AM

So if I understand this proposed add on, it's like a Cuttle Cart II but without feature of storing game bins. I do think this may need at least one game that actually uses these features to show what this can do. Perhaps a game built in with this or as a separate cart.

#9 Allan OFFLINE  

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Posted Fri Jun 12, 2009 9:33 AM

the fact that the expansion module is going to be supported in this way must indicate that enough 7800's are out there that had the expansion port buss internally (even if tramiels atari redesigned the case externally for the module to be sealed off)

I think he means a board inside of the case. I don't think he means anything connected to the 'Expansion Port'. Please correct me if I'm wrong.

Allan

#10 Allan OFFLINE  

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Posted Fri Jun 12, 2009 9:37 AM

As far as additional stuff...would it be possible to add a second Pokey like on the 8-bits. Is 16K the most you can add?

Allan

#11 nathanallan OFFLINE  

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Posted Fri Jun 12, 2009 10:07 AM

the fact that the expansion module is going to be supported in this way must indicate that enough 7800's are out there that had the expansion port buss internally (even if tramiels atari redesigned the case externally for the module to be sealed off)

I think he means a board inside of the case. I don't think he means anything connected to the 'Expansion Port'. Please correct me if I'm wrong.

Allan

Right, Curt was using the term but didn't mean the actual expansion slot on the side. Everything is going through the cart port.

I'll be saving up for this.

Nathan

#12 mos6507 OFFLINE  

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Posted Fri Jun 12, 2009 10:12 AM

Can you make the POKEY do I/O rather than just sound?

#13 gambler172 ONLINE  

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Posted Fri Jun 12, 2009 11:25 AM

I am going back to tackling the 13bit MCU used in the 7800 computer keyboard in August. In the meantime, I am considering a small 250-300 pc run of the Piggyback CPU module design originally proposed for the Atari 7800...

However, instead of a computer CPU this would be an expansion module, so far I will commit to the design the following features:

1. Built in High Score Cartridge capability (thanks to Pacmanplus and others, more and more games are now HSC enabled making this a more valuable feature to the system as a whole)
2. A 16K RAM upgrade
3. A Pokey Chip

The module is fairly roomy relatively speaking and there would be room for say an extra eprom and supporting discrete logic to have a built in game as well which would be over ridden when a cartridge was inserted a top of it.

Without going for pie in the sky wish lists and features, besides whats included above, is there anything else that should be a must have feature added to this Expansion Module? (Remember, it is limited to the data/address lines, Clk2, R/W lines, Ext Audio and IRQ lines... there is no video or anything else, so don't ask for something like enhanced video or some such nonsense that just can't be done through a cartridge port enhancement.



Curt

Hi Curt
Cannot wait to see this.Count me in for one.......
greetings Walter

#14 Tempest OFFLINE  

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Posted Fri Jun 12, 2009 11:29 AM

Maybe someone can add save game state support? Or Game Genie type ability?

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#15 Curt Vendel OFFLINE  

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Posted Fri Jun 12, 2009 12:57 PM

Hi Glenn,

There is no reason it can't do both, for sound, you need to use on the Pokey:

Pin 1 for GND, Pins 2,3,4,5,6 for Data D0-D7, Pin 7 for Clock2, Pin 17 for VCC, Pin 30 for A15, Pin 31 for A14 (Chip Select), Pin 32 goes to R/W Pins 33, 34, 35, 36 to Address lines A3 to A0 and of course Pin 37 which goes to EAUD (External Audio)

Now that still leaves all of the Keyboard and SIO pins free, so why not use it to its full potential...

My only concern is that once you start connecting keyboard lines and SIO lines to this and channeling it through the cartridge slot, that thing is going to generate some really nasty RFI which might in the end, make the video signal from the 7800 look really choppy.



Curt




Can you make the POKEY do I/O rather than just sound?



#16 nathanallan OFFLINE  

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Posted Fri Jun 12, 2009 12:58 PM

Can you make the POKEY do I/O rather than just sound?

Right, I was going to ask something similar, for rs-232 to be on there.

#17 Curt Vendel OFFLINE  

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Posted Fri Jun 12, 2009 2:25 PM

I've been out of touch with things for quite some while, I never even knew about the Xboard, I had to google Atari 7800 xboard and find out with its all about...


Now, not to rain on the Xboard, but to be honest - you could take Ballblazer, remove the rom chip, replace it with a 256K RAM chip, jumper cartridge line 1 - (R/W) to Pin 27 which would normally connect to A14, you'd remove that connection and move it over to Pin 1 and cut the +5v connection to it and you'd have yourself a Pokey/RAM cartridge...

Now you'd have just used up your cartridge slot, so that would be a problem, but you could do a stackable design like I did for the HSC and put a connection header on the top and pass thru the signals to a cartridge stacked ontop.




Curt

#18 nonner242 OFFLINE  

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Posted Fri Jun 12, 2009 2:33 PM

Whatever you do Im sure it would be something I would love to add to my 7800 collection..
Cant wait to read more..

#19 darthkur OFFLINE  

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Posted Fri Jun 12, 2009 4:30 PM

How many games would sound better due to the addition of the Pokey chip? I would assume that Beef Drop VE would act as the first edition with the pokey built in does.

#20 Greg2600 OFFLINE  

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Posted Fri Jun 12, 2009 5:03 PM

How many games would sound better due to the addition of the Pokey chip? I would assume that Beef Drop VE would act as the first edition with the pokey built in does.

That would be my laymen question, too. How does it improve pre-existing 7800 games? And obviously, how difficult to install? Will keep reading though.

#21 gdement OFFLINE  

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Posted Fri Jun 12, 2009 5:29 PM

How many games would sound better due to the addition of the Pokey chip? I would assume that Beef Drop VE would act as the first edition with the pokey built in does.

That would be my laymen question, too. How does it improve pre-existing 7800 games? And obviously, how difficult to install? Will keep reading though.


*If* the implementation is XBoard compatible, then it should improve sound on that game, and also on the Froggie demo.

#22 gdement OFFLINE  

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Posted Fri Jun 12, 2009 5:37 PM

The RAM/Pokey functions make it similar to what the XBoard does, so some compatibility with that would be useful.
Will it interface at the same addresses as the XBoard, and provide some easy way to detect the ram size (16kb instead of 128kb)?

Detecting ram size probably isn't a big deal though - you could just try storing different values in each XBoard bank and determine that the extra banks don't work.


I know a lot of people might not care about the XBoard and consider it "dead", but it does exist, a couple homebrew games support it, and if these devices perform similar functions there's no need for them to have incompatible interfaces.


If I remember correctly, the Xboard does not allow Maria access to the XBoard RAM as RAM but only ROM?
That would be one feature I'd hope to see changed if Curt tries to maintain compatibility with XBoard. My
guess is it would be possible to allow that RAM to act as both and still remain compatible....or do I completely
misunderstand the purpose of the RAM in the XBoard?

I'm not sure why it would have any such limitation. Maybe it's too slow for the Maria structures, but I doubt it. It's a modern surface mounted 128KB SRAM chip so I assume it's at least as fast as the 80's RAM in the console.

Of course the RAM is bankswitched in a 16KB window, so the Maria wouldn't be able to see any more than that at once.

I have an XBoard but haven't been able to experiment with it yet, as I can't seem to get it to work. I'll probably post a thread about that when I get things more organized.

#23 xZanU OFFLINE  

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Posted Sat Jun 13, 2009 8:23 AM

So in non-pin/slot/jumper/eprom/ram terms does this mean:

1. The ability to save our score for -any- game?
2. Better sound for -all- games?
3. Other? (Simple terms)

#24 mos6507 OFFLINE  

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Posted Sat Jun 13, 2009 8:58 AM

My only concern is that once you start connecting keyboard lines and SIO lines to this and channeling it through the cartridge slot, that thing is going to generate some really nasty RFI which might in the end, make the video signal from the 7800 look really choppy.


Even with an A/V mod?

#25 AdeptRapier OFFLINE  

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Posted Sat Jun 13, 2009 11:58 AM

Hey guys! Aside from programmers, how would this be of interest to the "average" 7800 user?

Thanks!!!

AdeptRapier

:)




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