Atari 800 RAM Selection

[fibrewire]

With a modded motherboard as posted above, the Bit 3 should work, but not the Axlon 128K. I could come up with a different mod for the 48K board that would work with the Axlon.

Keep your eyes peeled for a brown box in the mail. After my little "mishap" at work, everyone's stuff shipped on Monday. Only $242 in UPS fees

[fibrewire]

ClausB - Per your request.

Oh man! If that thing home-banked correctly, that would be a HUGE find to me. Any software come with it?

[fibrewire]

Greg I: I did a business search of the regular states with no luck. Then I found this when I looked in Colorado, but they are 1999 > Present.

 

Google Maps says the business is a house.

[Greg I]

Greg I: I did a business search of the regular states with no luck. Then I found this when I looked in Colorado, but they are 1999 > Present.

 

Google Maps says the business is a house.

 

Fiberwire, Thank you for checking. Unfortunately, no software or instructions came with it. That is why I was trying to find info about it. If you notice on the picture, there is a jumper block and I would love to know its function. As I mentioned, PaperClip, AtariWriter and some other programs do recognize the extra memory.

[fibrewire]

Fiberwire, Thank you for checking. Unfortunately, no software or instructions came with it. That is why I was trying to find info about it. If you notice on the picture, there is a jumper block and I would love to know its function. As I mentioned, PaperClip, AtariWriter and some other programs do recognize the extra memory.

Maybe the jumper limits the card to 128K? Google pointed me to this thread. Also Mathy's MyDOS page. I wonder how that card relates to the Axlon 256K RamDISK...

Also, the Axlon 128 switches between 16K and 128K with a toggle switch.

[ClausB]

Without laboriously tracing signals on your photos, but by checking the ICs' functions, we can make good guesses about how it works. The 8 DRAMs provide 256K RAM and have 8-bit refresh addresses. The 800 supplies only 7 bits of refresh but the 74LS112 probably supplies the 8th. The 74LS175 is a 4-bit register, enough to hold 4 banking bits for 16 16K banks. The 74LS133 is a big NAND gate just like the one on the AXLON 128K board which decodes the banking register addresses. The 2 LS158s and the LS153 multiplex the 9 DRAM address lines and the LS244 buffers the read data. The other 2 chips have inverters and gates for miscellaneous logic. R1 and L1 generate CAS timing.

 

So it looks like an Axlon-compatible 256K RAM card for slot 2 of the 800.

 

There is no RC circuit to reset the banking register, so it appears not to "home-bank". I don't see why that matters because when DOS loads, the byte at address $0FFF initializes the register.

Edited June 25, 2011 by ClausB

[Greg I]

Without laboriously tracing signals on your photos, but by checking the ICs' functions, we can make good guesses about how it works. The 8 DRAMs provide 256K RAM and have 8-bit refresh addresses. The 800 supplies only 7 bits of refresh but the 74LS112 probably supplies the 8th. The 74LS175 is a 4-bit register, enough to hold 4 banking bits for 16 16K banks. The 74LS133 is a big NAND gate just like the one on the AXLON 128K board which decodes the banking register addresses. The 2 LS158s and the LS153 multiplex the 9 DRAM address lines and the LS244 buffers the read data. The other 2 chips have inverters and gates for miscellaneous logic. R1 and L1 generate CAS timing.

 

So it looks like an Axlon-compatible 256K RAM card for slot 2 of the 800.

 

There is no RC circuit to reset the banking register, so it appears not to "home-bank". I don't see why that matters because when DOS loads, the byte at address $0FFF initializes the register.

 

ClausB, Thank you for your excellent assessment! I appreciate your effort. I was concerned about Axlon compatibility as my Happy v7 software would not recognize the extra memory (it says in the instructions that it will only recognize Axlon compatible memory). It may be beause this is an 800 rather than an XL/XE.

[stevem00]

Can anyone identify the manufacturer of this RAM card and the specs?

[Rybags]

4116 ICs by the look of the pic. They're 16 kbit chips, each provides 1 bit per access.

 

16K RAM module.

[fibrewire]

Does anyone own or have information about the Axlon RamCram Plus 48K? Apparently there were no jumper wires to solder, and it just plugged straight into the Atari 400. Unfortunately, information seems limited about this board.

 

It would be cool if it worked with the Axlon RamDisk 128K in an Atari 800.

 

http://gury.atari8.info/details_hardware/132.htm

[ClausB]

Does anyone own or have information about the Axlon RamCram Plus 48K? Apparently there were no jumper wires to solder, and it just plugged straight into the Atari 400.

The 400's RAM slot does not have enough select signals to address 48K nor does it have the logic to deselect RAM when a cart is present. That's why all the 48K mods require jumpers added to the motherboard. However I do recall seeing a photo somewhere of a plate that presses on to the underside of the motherboard and works supposedly without solder.

 

Theoretically you could design a RAM upgrade that does not require select and deselect logic. Taking a cue from the good old Sinclair ZX80, you could connect the RAM data lines through series resistors to the Atari's data bus. You would size the resistors to be strong enough to drive the data bus when nothing else does, but weak enough not to overcome any other device (ROM, ANTIC, GTIA, etc.) driving the bus. Then RAM would fill every hole in the memory map!

[ClausB]

I would like to use Bit 3 in slot 3, Axlon 128 in slot 2, and a modded Atari 48K card in slot 1.

With a modded motherboard as posted above, the Bit 3 should work, but not the Axlon 128K. I could come up with a different mod for the 48K board that would work with the Axlon.

Here's a mod for the Atari 48K board that should work in slot 1 with the Axlon 128K in slot 2 and any non-RAM board in slot 3. It only uses 32K of the 48K board, and the whole system would have 48K base RAM plus 112K banked.

 

1. Remove the 74LS32 chip from socket U15 and the 74LS30 chip from U13.

 

2. Unsolder and lift the lower end of R14.

 

3. On the back of the board, solder a small wire between pins 1 and 3 of U15.

 

4. Solder a small wire between pins 1 and 12 of U13.

 

5. Solder a small wire between pins 4 and 12 of U13.

 

6. Plug the 74LS30 chip back into U13. Store the 74LS32 chip safely away and leave U15 empty.

 

Photos:

[ClausB]

Here's a mod for the Atari 48K board that should work in slot 1 with the Axlon 128K in slot 2 and any non-RAM board in slot 3. It only uses 32K of the 48K board, and the whole system would have 48K base RAM plus 112K banked.

Just to be clear: This mod to the 48K board does not require any modification to the motherboard nor to any other board.

[1050]

Thanks Claus, it's great to have to you have you in the forum like this. But I'm curious about how your 48K board says right on it 64K RAM assy NO CAO61553? Rev A no less. I'm wondering at this point who was it that couldn't count right? Somewhere someone made a mistake? Or not?

 

I don't recall every seeing this particular board before but then I'm not really an 800 power user, just very curious as I have several and like them very much. Another question I have about 800s is just what did Jay Miner do to his version of the 800, and/or where could I read up on it in detail? Google just wants me to read about his Amiga stuff, and I'm not interested in that part.

[fibrewire]

But I'm curious about how your 48K board says right on it 64K RAM assy NO CAO61553?

IIRC, the board does have 64K on it, but the Atari 800 can only address 48K contiguously. Over that, it uses a 16K window to page in and out of. Later 8-bits utilize PortB from Joystick Ports 3 & 4 to access larger contiguous memory from 64K up to 128K. That is why the XL and XE line only have two joystick ports.

 

Another question I have about 800s is just what did Jay Miner do to his version of the 800, and/or where could I read up on it in detail?

Jay Miner designed the TIA for VCS, and the ANTIC and CTIA for the 400/800. I guess the guy doesn't like to talk about his tenure at Atari

[ClausB]

That's right. By 1983 one row of 64K DRAM chips was cheaper than 3 rows of 16K so it made sense to use only 3/4 of the 64K.

 

I am presently working on other mods to this board for the 800:

48K stand alone

52K contiguous

64K XL compatible

 

Miner lead the group that designed the custom chips for the 800. All 800s use those chips, as do the 400, 5200, all XLs, and XEs. So the phrase "Jay Miner 800" is a bit redundant.

[1050]

Thanks, guys. The fog has lifted entirely and I'll be watching for more installments of 800 lore. Can't get enough.

[fibrewire]

I don't know how the memory address works - could 4 of the 4164 chips be used to make a 32K board?

 

Or perhaps a 32K x 8 like this one could be used...

 

eBay Auction -- Item Number: 310324477816

[Rybags]

They only output 1 bit per chip, so I'd say no.

 

One of the BBC low-end models actually uses a single 4-bit 64K DRAM to give 32K but it buffers each half of the byte and puts it on the bus, IIRC with the CPU going through a long cycle time.

 

That kind of thing won't work on Atari, at least not easily.

 

Way easier to just use a pair of 4-bit DRAMS - they don't plug into 1-bit chip sockets, you need to supply 1 bit to each, tie the unused Ras/Cas select to GND.

 

On the other hand, 30 pin SIMMs are practically worthless and could probably be used too.

 

ed - Static RAM probably no go either. That uses direct address input rather than Ras/Cas.

 

Datasheet here http://www.datasheetcatalog.com/datasheets_pdf/6/2/2/5/62256.shtml

Edited July 4, 2011 by Rybags

[fibrewire]

Thanks! I was thinking about that clock card I saw on eBay, and thought it would be nice to have that + 32K ram card. The 4-bit DRAMS sound like the way to go.

[Rybags]

Another alternative might be 64k x 1 bit chips but not sure if they're pin compatible with whatever they'd be replacing.

[ClausB]

What board are you thinking of putting those chips onto? The most common board, of course, is the Atari 16K. My original article describes how to modify it for 64K x 1 DRAMs (ignore the 400-specific parts). You could make a 32K or 48K board out of that with minimal additional circuitry.

 

The 64K x 4-bit DRAMs (4464) are partly pin-compatible with the 64K x 1 chips (4164) but they require more than 7 bits refresh address, which is all the older ANTIC in the 800 provides. So it would be a complex mod to use those.

 

The 32K x 8 SRAM is really a good choice. They're not at all compatible with DRAMs so you would not use them on a RAM board, but they are nearly pin-compatible with Atari ROMs. It would be not too hard to add one directly to the 10K OS ROM board. I have a few of those chips from a dead '486 PC and have thought a bit about using them this way. If there's interest I'll post a design.

[fibrewire]

Nice! That sounds like a good mod for a RAMROD board. Too bad PortB is still required for 128K with SRAM.

 

http://www.atariage.com/forums/topic/182682-details-of-dual-os-newell-ramrod-board/page__view__findpost__p__2298565

[ClausB]

I finally finished the schematic for the Atari 400 48K board:

 

[fibrewire]

Great job! Thank you so much - I can't find the 48K board I kept, but when I find it I will try it!