7800 Dev System mod question

[Tickled_Pink]

Looking at changing the ROM around on one of my 7800 machines to turn it into a dev system. According to the instructions I have, on some machines Atari put EPROMs into the machines (doubt they're actual EPROMs, more like pin-compatible PROMs). The models listed where these were apparently used were C300633 and C070856.

 

Just opened one of my machines and, lo and behold, it has the C300633 board. Unfortunately the instructions don't mention which one on this board is the right one to remove. So I'm just asking if anyone can confirm that it's the socketed 28-pin chip at the front marked C300558 - the rest are pretty identifiable (the 6502, 6532, 2 x 6116 RAM chips, and the other two I'm not too sure about but seem to have far too many pins).

[+Mitch]

Looking at changing the ROM around on one of my 7800 machines to turn it into a dev system. According to the instructions I have, on some machines Atari put EPROMs into the machines (doubt they're actual EPROMs, more like pin-compatible PROMs). The models listed where these were apparently used were C300633 and C070856.

 

Just opened one of my machines and, lo and behold, it has the C300633 board. Unfortunately the instructions don't mention which one on this board is the right one to remove. So I'm just asking if anyone can confirm that it's the socketed 28-pin chip at the front marked C300558 - the rest are pretty identifiable (the 6502, 6532, 2 x 6116 RAM chips, and the other two I'm not too sure about but seem to have far too many pins).

 

I have one with an EPROM and it is definately an EPROM not a otPROM. If it has a white label it is probably an EPROM if the part number is printed on the chip like a standard ROM then it most likely is. If you're still not sure, a picture would help.

 

Mitch

[Tickled_Pink]

I think you're right. Looking at the instructions again, it says that only those model boards made around 1989 had the EPROM.

 

But if the board model is the same, then any OTP ROM would have to be pin compatible with an EPROM. Unless there were certain revisions of the board model. Now I'm confused.

 

I pulled apart two machines last night. One just had the ROM in its socket, the other had the same but also a wire leading from a resistor to pin-27 on the ROM, which I assumed was to fix an error on the board. I'll compare the two next to each other later.

[Eckhard Stolberg]

The PAL 7800s can use either an EPROM or a masked ROM for the BIOS. To handle the different pinout of the chips there are two jumpers in the front-right corner of the board labled W5 and W6. One of them is closed with one of those parts that looks like a resistor with only a black ring. The other jumper is open. If W5 is open and W6 is closed, then the board uses a masked ROM. If W5 is closed and W6 is open, then the board uses an EPROM. So moving the W6 jumper to W5 and sticking a DevOS EPROM into the BIOS socket should be all that is needed for your modification.

 

You should remember though that the PC transfer software is pretty old by now and only really works on DOS or DOS-based versions of Windows.

 

 

Ciao, Eckhard Stolberg

[Tickled_Pink]

Thanks Eckhard. It explains a few things.

 

Only problem I've got now is that my EPROM eraser managed to blow its tube yesterday! Gaaaaaa!!!!

[mimo]

Thanks Eckhard. It explains a few things.

 

Only problem I've got now is that my EPROM eraser managed to blow its tube yesterday! Gaaaaaa!!!!

 

Hey, let me know how you get on, I have 3 PAL systems here and I want to do this mod to one of them.

Which cart do you plan on building?

 

Oh, and if you need an erased eprom, I can do one for you.

[Tickled_Pink]

Thanks mimo. I think I have a VERY tatty Hat Trick cart here somewhere which should do the job. Haven't got the exact static RAM to use for the job, though. All the ones I have are nvSRAM - got a couple of pieces of pretty expensive 2mbit Dallas battery backed nvSRAM and some cheaper (and smaller) Simtek nvSRAM (can't remember the size).

 

I'll try and find the Simtek RAM and see if one of those can be shoehorned into a proto. If not then I'll probably etch a new board design.

 

We've got a sunbed ... how long will it take to wipe the eproms with that? An £800 eprom eraser.

 

If that doesn't work, I'll send you some to work on for me.

[mimo]

Ok, hope you get a nice tan whilst erasing the chip

Looks like finding the sram may be harder than I thought, any ideas where I might get some?

[+Mitch]

Ok, hope you get a nice tan whilst erasing the chip

Looks like finding the sram may be harder than I thought, any ideas where I might get some?

 

If you are talking about the 62256 SRAM chips, old junk motherboards may have some, think 486 time frame. A big electronics dealer should have them, JDR in the US sells them online for a couple bucks.

Also, an updated version of the RAM cart instructions is available here.

 

Mitch

[gdement]

Thanks mimo. I think I have a VERY tatty Hat Trick cart here somewhere which should do the job. Haven't got the exact static RAM to use for the job, though. All the ones I have are nvSRAM - got a couple of pieces of pretty expensive 2mbit Dallas battery backed nvSRAM and some cheaper (and smaller) Simtek nvSRAM (can't remember the size).

 

I'll try and find the Simtek RAM and see if one of those can be shoehorned into a proto. If not then I'll probably etch a new board design.

Actually, nvram seems like a much better idea than using volatile sram. If the pinout is workable, I'd try using that (socketed of course).

 

We've got a sunbed ... how long will it take to wipe the eproms with that? An £800 eprom eraser.

A sunbed will filter out the very wavelength which you need to erase an eprom, so it reportedly won't work very well. Silly safety features ruin all the fun.

 

If you are talking about the 62256 SRAM chips, old junk motherboards may have some, think 486 time frame.

I've got some of those which I pulled from my old 486, but I don't know if they actually work. The manufacturer of that board (PCChips) was known for using fake cache chips - just empty plastic DIPs with nothing inside.

[Tickled_Pink]

Ok, hope you get a nice tan whilst erasing the chip

Looks like finding the sram may be harder than I thought, any ideas where I might get some?

You're right. I was surprised how hard it is to find the right chips. ESR Electronics only have 64K SRAMs but I don't know if they're 64K-bit or byte. Same as have Maplins. Even RS seem to be a non-starter. Only Farnell seem to have a half-decent range, but they're predominantly distributors so don't know if they'd be willing to sell to private customers. You could try something else ... I got my Simtek and Dallas SRAMs as free samples from the manufacturers (worked out the other day that I managed to get my hands on £500 worth of electronic components this way ).

 

Also, an updated version of the RAM cart instructions is available here.

 

Mitch

 

Thanks. The PDF file linked to on that page is a beauty.

 

We've got a sunbed ... how long will it take to wipe the eproms with that? An £800 eprom eraser.

A sunbed will filter out the very wavelength which you need to erase an eprom, so it reportedly won't work very well. Silly safety features ruin all the fun.

Dammit. How long will it take to erase them by sunlight in the great British Autumn?

 

The Simtek RAMs I have are 256K-bit (32K-byte). They're pin compatible with battery backed SRAMs by Dallas. They're not that cheap (but much cheaper than Dallas). Think they're about £9 each at Farnell. If you can't find Simtek, try finding Cypress' versions. They're identical in that they've licensed the technology from Simtek. Cypress are a bigger manufacturer so chances are you might be able to find these if you can't find the Simtek RAMs.

 

Simtek STK16C88 Datasheet.

 

Or you can use a Flash for a flash cart instead.

Edited October 27, 2007 by Tickled_Pink

[gdement]

The Simtek RAMs I have are 256K-bit (32K-byte). They're pin compatible with battery backed SRAMs by Dallas. They're not that cheap (but much cheaper than Dallas). Think they're about £9 each at Farnell. If you can't find Simtek, try finding Cypress' versions. They're identical in that they've licensed the technology from Simtek. Cypress are a bigger manufacturer so chances are you might be able to find these if you can't find the Simtek RAMs.

 

Simtek STK16C88 Datasheet.

 

So those simteks are also nonvolatile, I see. I apparently misread your previous post. Those look cool, never seen that datasheet before - thanks for posting that. They also look like they'll actually fit inside a cartridge, unlike the Dallas chips, so they could be used in homemade games.

[Tickled_Pink]

Been thinking about the bank switching decoding methods. Seems that every 'complex' multicart or ram cart design I see uses a GAL or other programmable logic to help with the bank switching. Looking at the current designs for the 7800 dev system carts, none seem to be able to handle everything thrown at them. Just wondering if anyone's thought about using a small Microcontroller instead of a GAL, which might provide more scope for implementing the extra currently unsupported bank switching methods.

 

I've seen a Vectrex multicart design that uses a PIC for bankswitching.

[carmel_andrews]

TP...are you using an ST as part of the 7800 development system...I heard that the ST was Atari's prefered 7800 software development system (but i could be wrong)

[Tickled_Pink]

At the minute I'm not really looking at developing on the thing - yet. Won't have time with all the other projects in the works. Maybe in the future.

 

Not sure which is best, though. I'm going to put a third desktop PC up in the bedroom at some point (just need a case and memory) so won't have room to put an ST there as well.