1088NUC+: A Memory Upgrade for the 576NUC+

[+mytek]

My 576NUC+ system now has a bigger brain

 

Well not really, but it does have twice as much extended memory. Counting the 64K base RAM that brings it up to a grand total of 1088K to be exact. So I guess that makes it a 1088NUC+

 

Thanks to @tf_hh there is a relatively simple way to do this. Well that is if soldering two 32 pin RAM chips together in a piggyback fashion is simple for you   But there are only 3 jumper wires required, which is pretty simple.

 

 

Santronic's XRAM Test Results (1024K Extended + 64K base RAM = 1088K)

 

And we can now load and run AtariBlast straight from the SD card - that's a first for this system!

AtariBlast! is the killer app, and the main reason for having 1MB of RAM, which allows you to load and run the xex version of the game. If you already have the 576NUC+CART version of the system, there really isn't much need to do this upgrade since not much else needs that kinda RAM, and you can simply run the cartridge version of the game instead.

 

I loaded this game with my SDrive set to divisor 0, and it accomplished it fairly fast, probably on the order of less than 2 minutes. I'll time it tomorrow and report back here on exactly how long it does take. EDIT: It took exactly 1 Minute and 34 seconds to load.

 

However I seriously doubt that this mod could be done on the 576NUC+ Cart version because of the limited space available, but I could be wrong (I don't have one to check against). But on the base model with or without Fujinet or the SDrive Simple daughter boards it'll work just fine. And that would be the system that needs this the most for running 1MB games and applications.

 

Anyway I have some more extensive tests to run to be sure this is truly stable and compatible. But if everything checks out I'll upload @tf_hh's 1MB EMMU JED file and the instructions.

[Panther]

Ha!  I have a copule of AS6C4008-55PCN in stock!

 

[+mytek]

6 hours ago, Panther said:

Ha!  I have a copule of AS6C4008-55PCN in stock!

Cool!

 

Yeah I was trying to think of a way to make a piggyback board for this, but because of the tight spacing and the need to break-out certain pins, I just don't think that would be possible or practical. Besides it would actually require much more soldering to assemble such a board vs. the way I ended up doing it. I'll still play around with the idea, but nobody should hold out much hope for that.

[Panther]

I was just looking at it and there is 9.2mm of space above the Atari chips, minus the length of the pins sticking out under the FujiNet or SDrive, and I think it can absolutely be done with an oddly shaped PCB that has headers to plug in place of the SRAM, PIA, and PLDs, then moving these chips to the add-on board with an extra SRAM, but I'm just not seeing the practicality of it.  Just piggybacking them and making the few connections as you've done just seems better.

 

[+mytek]

2 hours ago, Panther said:

I was just looking at it and there is 9.2mm of space above the Atari chips, minus the length of the pins sticking out under the FujiNet or SDrive, and I think it can absolutely be done with an oddly shaped PCB that has headers to plug in place of the SRAM, PIA, and PLDs, then moving these chips to the add-on board with an extra SRAM, but I'm just not seeing the practicality of it.  Just piggybacking them and making the few connections as you've done just seems better.

If all that needed to be done is to be able to electrically connect to the pins of the 3 chips, then it would be a simple matter of using a thin PCB material and mounting 3 machine pin sockets on that board. But since we need to isolate at least one pin on all 3 chips that means having to use double machine pin headers -and- individual sockets that are offset from the headers enough to allow being able to obtain that electrical isolation where desired. I just don't think there is enough room between the MMU and the EMMU to achieve that in any practical way. And yes it would also be a lot of soldering for whoever assembles the board, on the order of 3 times as much than what was required in my example.

 

Actually I found soldering the RAM chips together to be quite easy, and that really is the hardest part. So I'm in total agreement with the last sentence of your post

[+mytek]

It looks like this thing is ready for prime time.

 

I spent sometime yesterday and this morning to create a variant of the TKII firmware that is flashed into the PIC16F1847 chip on the 576NUC+. Although the memory upgrade will work with the existing firmware, it'll now be a little less clunky. Let me explain why... Because of what needed to be done to double the extended RAM from 512K to 1024K, when in 1MB mode the 4 language slots are no longer present. However when in the normal 576 mode everything is as it was before the upgrade. So with the old firmware in play, If you were to switch to 1MB mode via the CTRL+ALT+X toggle function, the languages would not work correctly, and furthermore if one of the language slot activation key sequences was pressed (ALT+1-4) it would simply dump you into the operating system without a language.

 

So with the new TKII firmware I've eliminated the RAM mode selection toggle (CTRL+ALT+X) and have put RAM selection into an automatic mode. So now if you press ALT+~ (tilde) you will boot with 1088K and no language support, whereas if you select a language slot (ALT+1-4) 576K of RAM will be invoked with the language that matches your selection. That's it -- very straight forward and simple. So I highly recommend upgrading the firmware if you decide to also upgrade the memory.

 

Here's everything you should need to get you going (contains new JED file, new TKII firmware, and instructions):  1088NUC+ Upgrade.zip

Contains Updated TKNUC1MB Firmware now at Version 2.1 compiled on March 14th 2023 -- NOT FOR USE IN THE ORIGINAL 576K SYSTEM.

[Panther]

I was going to do this, then I thought about it and I really don't know of anything I would run on the 576NUC+ that needs 1MB of RAM, and it's just so clean looking as is.  I can't bring myself to bend pins and add wires.

 

[+mytek]

On 3/13/2023 at 9:45 PM, Panther said:

I was going to do this, then I thought about it and I really don't know of anything I would run on the 576NUC+ that needs 1MB of RAM, and it's just so clean looking as is.  I can't bring myself to bend pins and add wires.

Well for me the deciding factor was to be able to run AtariBlast!  EDIT: this refers to the XEX version that can be run from the SD card, thus not requiring a cartridge.

 

And for $7 in parts it's well worth it. But you gotta weigh that against having a couple of bent up pins and 3 jumper wires. Although I think my lash-up looks pretty decent. I should probably mention that those bent up pins need to be cut fairly short so that they don't interfere with the Internal SIO Header or electrically short out to an adjacent pin on another chip. Check out the pics I posted when I first started this thread to get an idea of how short I'm actually talking about. Of course that means those chips won't be easily reprogrammed, but that stuff is pretty solid.

 

BTW, I pulled that download I posted earlier because I forgot that I wanted to fix a couple of other issues with the TKII code while I was in there. A new download will be up tomorrow (done)

[Panther]

2 hours ago, mytek said:

BTW, I pulled that download I posted earlier because I forgot that I wanted to fix a couple of other issues with the TKII code while I was in there. A new download will be up tomorrow

I've not been playing Atari games much in quite awhile, or even much in the way of PC or VR games lately.  Just so much going on I guess.  I guess I'll have the SRAM here and available for if I ever do decide I need this.  As for the TK-II code, is this anything that you might also be changing in the regular (576K) version?

 

[+mytek]

7 hours ago, Panther said:

As for the TK-II code, is this anything that you might also be changing in the regular (576K) version?

Yeah I probably should. It isn't a big deal, but the right ALT key sometimes gets a bit confused about whether it got pressed and sometimes needs to be pressed again to properly register. It has to do with what I call an 'extended' key flag that didn't get cleared in the TKII's key processing routine. Believe me this wasn't easy to pin down as to being the cause, but once discovered is very easy to fix in the firmware. Since I started off at version 2.0 when I modified the original TKIINUC firmware to be the TKNUC1MB firmware, it'll get bumped up to V2.1 when released today. I'll bump up the original firmware the same when I add the fix to it.

 

I'll likely do that when I eventually update the project's firmware download at my AtariBits website.

[+mytek]

A new expansion board is in the works that will provide this extended memory configuration for 1088K, and so much more...