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Curt Vendel

7800 Expansion Module

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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.

 

That all might be true but if I remember correctly(as it was a while ago),I asked the developer of the unit if it could use

the extra as Maria ram and I believe he told me it was to emulte ROM only. Perhaps he did not hookup the write line

to the 7800.

 

The Maria always just reads anyway, it never writes (like Mord was saying).

But I suddenly remembered something and just checked the programming specs. I'm guessing this is what the developer would have been talking about:

 

...<holey-DMA blah blah>...

MARIA can be told to interpret odd 4K blocks as zeros, for 16 high zones, or odd 2K blocks as zeros for 8 high zones. This will only work for addresses above x '8000'.

 

So holey DMA won't work in addresses below $8000 - and the XBoard RAM (and all carts that have RAM) sits below that. So if you need holey DMA then you can't put those graphics below $8000.

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...<holey-DMA blah blah>...

MARIA can be told to interpret odd 4K blocks as zeros, for 16 high zones, or odd 2K blocks as zeros for 8 high zones. This will only work for addresses above x '8000'.

 

So holey DMA won't work in addresses below $8000 - and the XBoard RAM (and all carts that have RAM) sits below that. So if you need holey DMA then you can't put those graphics below $8000.

 

I found that one out the hard way while making Super Pac-Man. :(

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I am taking care of a few things at the end of the month, I was going to work on a 1090 XL project, but I'm backburning that to focus on the 7800 expander.

 

I'll have some initial plastics done by end of July and by that type I should have a fully debugged pcb ready, so I'll have some stuff to show at the end of July and if all looks good, then August would be the target to start shipments.

 

 

Curt

 

That expansion module looks pretty cool. I like how it looks like a miniature 7800, although I was hoping it would be a little more flush to the 7800. When can we expect to see the finished product?

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I am taking care of a few things at the end of the month, I was going to work on a 1090 XL project, but I'm backburning that to focus on the 7800 expander.

 

I'll have some initial plastics done by end of July and by that type I should have a fully debugged pcb ready, so I'll have some stuff to show at the end of July and if all looks good, then August would be the target to start shipments.

 

 

Curt

 

That expansion module looks pretty cool. I like how it looks like a miniature 7800, although I was hoping it would be a little more flush to the 7800. When can we expect to see the finished product?

Right in time for my birthday, nice! Count me in as a potential buyer as well!

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Since the expansion module has the ability to work with A8 i/o devices i am guessing you will make a version of ataridos/spartados x for the 7800 on cartridge

 

Also, will any proposed keyboard also feature the console keys, or will that be routed though to the 7800 console keys

Edited by carmel_andrews

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Considering that one of the goals of this is to hook up a keyboard and peripherals to it and turn it into a computer, would it be that difficult to add a internal clock chip so that maybe one day a DOS might be written that has a date/time stamp? I would imagine that with todays technology there must be simple 'clock on a chip' devices that could be added to the board. I know it wouldn't be very useful for games but it would be great for other types of software.

 

Allan

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I am taking care of a few things at the end of the month, I was going to work on a 1090 XL project, but I'm backburning that to focus on the 7800 expander.

 

I'll have some initial plastics done by end of July and by that type I should have a fully debugged pcb ready, so I'll have some stuff to show at the end of July and if all looks good, then August would be the target to start shipments.

 

 

Curt

 

 

This sounds like a really cool project. Do you think maybe by that time you will be shipping last years project? Maybe finish what you started and took money up front for before you ask for more?

 

I see you hope to start selling in July, so that means if I prepay for one maybe I'll have it September 2010?

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Please sign me up for one. Looks like the coolest thing I have seen in a long time!

Thanks Curt!

 

1090XL project sounds great too! :D

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Well, no one is signing up for anything, like I say I need to wrap up the first product I had going at the end of the month and clear the decks, now that it looks like I'm not going to have to go for another (and another, and another....) heart surgery like I had 3 times over the past year, well now its time to get back on track, clear the decks and make time for new stuff... so for now, lets keep this as a progress watch thread, lets get some hog outs of the plastics done, I'll work on the first go around of the PCB and post it up and if things hit a snag or someone see's a way of improving things, we can work on doing some changes and improvements. I am going to put together in 2 weeks for simple down and dirty 16K carts and I'd like to hear from anyone working on a game, that thinks they could be ready by around say Mid to late august that could use the extra memory or wants to utilize the Pokey (I think the source code of all of the versions of Commando I posted up early last week should prove invaluable in how to access the Pokey and not access it when not available for programmers to start to look into pokey enabling their audio on their games.)

 

Got a lot to do and need to clear out open promises to those who ordered my joysticks many months ago, so think of this thread as a work in progress design discussion and updates, when things start to solidify we can all start talking then about ordering them for immediate shipment.

 

 

Curt

 

sign me up for one. I am very excited for this project. Thanks, John

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I am going to put together in 2 weeks for simple down and dirty 16K carts and I'd like to hear from anyone working on a game, that thinks they could be ready by around say Mid to late august that could use the extra memory or wants to utilize the Pokey

(I think the source code of all of the versions of Commando I posted up early last week should prove invaluable in how to access the Pokey and not access it when not available for programmers to start to look into pokey enabling their audio on their games.)

 

 

Using the Pokey is no biggie(or not using it) but as far as anything ready by August, not likely since, I can't try using

the extra RAM on Maria trick. Otherwise the games will lack interesting back drops and other gfx effects they could have.

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This is why brought the idea for the extra controller ports.

 

If you want extra controller inputs then you need a PIA as well. The POKEY will only allow pots and a keyboard, or maybe 5200 controllers ;)

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This is why brought the idea for the extra controller ports.

 

If you want extra controller inputs then you need a PIA as well. The POKEY will only allow pots and a keyboard, or maybe 5200 controllers ;)

 

Pots? As in paddle controls? I remember somebody saying paddle games made for the 7800 would difficult or was it impossible.

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Pots? As in paddle controls? I remember somebody saying paddle games made for the 7800 would difficult or was it impossible.

 

Yes, potentiometers, I don't know why it would have been an issue doing these on the 7800, TIA already supported 2 pairs of padles (which technically could also allow 2 analog joysticks wired to the paddle pots), the only possible problem I can think of would be possibly using the TIA bus more often (which can cause performance hits on the CPU as it has to drop down to 1.19 MHz when accessing 2600 hardware), of course this already has to be done when reading joysticks and generating sound.

 

 

On the previous thought: couldn't you configure the keyboard readout for POKEY to support additional controllers?

This came up in another thread (see below) on the 7800 recently (actually it was a question pertaining to POKEY handling I/O in general on-cart), and the answer I got was that you could add additional ports to a POKEY expansion cart (or full sized add-on as is being proposed here), but it wouldn't be able to access the two existing controller ports.

 

Technically you probably -could- use the I/O of a pokey on a cartridge setup, but that would mean you would have to be able to plug your controllers into the cartridge. Would look odd to say the least, plus one unfortunate yank on the cord and your cartridge goes flying across the room.

 

Gumby was suppose to be a lowcost soundchip, but since they had to downsize it's expectations several times until it was just up and cancelled, I could only assume it wasn't intended to be a cutdown pokey. I wonder if they would have had time to finish the sound part of it if they just repackaged a pokey chip's sound into a properly sized chip. After that mandate their use in 7800 games to ensure there was a sizable demand for the new chips to drop the price per chip. ;) Then later in the system's life either release the new Gumby or even do a doubled up pokey chip that had 8 channels prior to Gumby.

Edited by kool kitty89

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Pots? As in paddle controls? I remember somebody saying paddle games made for the 7800 would difficult or was it impossible.

 

Yes, potentiometers, I don't know why it would have been an issue doing these on the 7800, TIA already supported 2 pairs of padles (which technically could also allow 2 analog joysticks wired to the paddle pots), the only possible problem I can think of would be possibly using the TIA bus more often (which can cause performance hits on the CPU as it has to drop down to 1.19 MHz when accessing 2600 hardware), of course this already has to be done when reading joysticks and generating sound.

 

This thread is seem to have what I'm talking about. It was about the lack of paddle games for the 7800.

 

More to the point, I'm talking about this post by Supercat.

 

To read paddles, one must poll them at precise spots on the frame. On the 2600, the code always knows where the beam is during the kernel. If it has enough cycles to read the pots mid-kernel it can do so. On the 7800, code generally does not chase the beam. An Atari 7800 game could be made to chase the beam, but it would add about a 10%-25% CPU load to read one paddle per frame, or a 75% CPU load to read more than one.

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But isn't that the whole idea behind POKEY, to have the coprocessor poll the paddles and just report back a number between 0 and 227?

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Well, I'm not a tech dude. I didn't even know that the Pokey made using paddles for 7800 games more practical until I read this thread. Still the thought of seeing games like Pong, Breakout, and Warlords does look very interesting.

Edited by Bakasama

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