Could ColecoVision's 8K RAM space be utilized

[+mytek]

I was looking at the memory map for the CV and it appears that $6000-$7FFF gets selected for the CPU RAM via the 74LS138 decoder. That's a total of 8K. So could something like a AS6C6264-55PCN (8Kx8 Static RAM) be substituted for the two existing 2114 (1Kx4) SRAMs without conflict if the additional address lines were brought over and connected  to A10-A12. So in other words I would be looking at using only one of the bigger RAMs to replace both of the existing smaller RAMs.

Digi-Key LINK

 

So besides being concerned with creating a conflict with existing games, would there be any benefit to having the additional 7K of RAM available?

[digress]

I think the homebrew SGM extra ram has so many compatible games using it now that it would be better to just stick with that design. 

 

It is interesting what you say. I wondered about that 7kb myself. A solution already exists though.

[+mytek]

Thank you for the quick reply.

 

After I posted I stumbled across the SGM aspect, which looks very interesting indeed. Are there any schematics for the SGM online? Also curious if the SGM uses that portion of RAM as well (I think I recall reading something about it having 16K, but I could be wrong).

 

I'm exploring options for a DIY CV, and for the money the 8Kx8 SRAM I posted is probably close to the same as two 2114 off the used market, whereas the AS6C6264-55PCN is still being made and available from Digi-Key and Mouser, as well as others. And to top it off it'll require less space and 8 fewer pin connections. But it would be nice if the extra 7K were usable.

[Pixelboy]

58 minutes ago, Captain Cozmos said:

I have yet to find a single game that has been created exclusively for the Colecovision that uses the SGM which was not a port.  I could be wrong, please do not scold me.

Children of the Night was made for ColecoVision first, if I remember correctly, but the MSX version was made very soon after (perhaps even in parallel). Same goes for Mecha-9. There's also Wizard of Wor which was coded for the ColecoVision first, and was ported to MSX later. The only Team Pixelboy SGM-dependent game coded from scratch which was not ported to MSX is Asteroids.

 

Consider yourself scolded. 

 

[Captain Cozmos]

12 minutes ago, Pixelboy said:

Children of the Night was made for ColecoVision first, if I remember correctly, but the MSX version was made very soon after (perhaps even in parallel). Same goes for Mecha-9. There's also Wizard of Wor which was coded for the ColecoVision first, and was ported to MSX later. The only Team Pixelboy SGM-dependent game coded from scratch which was not ported to MSX is Asteroids.

 

Consider yourself scolded. 

 

I stand corrected.
Hopefully people will utilize it more.
 

If Dino Eggs does well I might update it to a super game.
I just picked up a fair amount of 256k TSOP chips on the cheap and would like to create a mega cartridge unless I use them in another project.

 

[+mytek]

On 9/19/2022 at 2:15 PM, Captain Cozmos said:

By asking if it is possible, I would conclude that you have limited experience in electronics. 

Well yes I have limited experience with the CV, but not limited experience in electronics. If you are at all curious, check out my website (in signature) to get a glimpse into my actual experience. However I've been very Atari centric for the last 7 years, so the CV is something quite new to me, hence the questions I am asking.

 

I did find a good breakdown on the SGM which is very useful...

 

So it would appear that if I were to AND the select bits for $2000-$6000 and use a 32K cache ram I would then have 24K of mapped ram available in the CV, making it look like an Adam in that regard. there would still be 8K missing from that map due to the BIOS, but it appears that could be switched out for ram as well with a bit of added logic.

 

 

On 9/19/2022 at 2:15 PM, Captain Cozmos said:

I am not trying to put you down by any means.

So instead of opening up your Colecovision and de-soldering things, the SGM is your best route if you are compelled to go down this road.

I didn't take any offense, but it simply wasn't true.

 

Actually I have been experimenting on a real CV system, with the first order being to clean up the video (RF left the building, and in walks S-Video). Here's what I have done on that thus far...

EDIT: The design in this schematic isn't quite right, and has since been improved. There is also a new topic that was started on this specific video upgrade where I'll be adding updated information and schematics.

 

It was very interesting when I stumbled on the idea to use the LM1889N modulator chip for only it's color encoder function. Then I just needed to appropriately amplify the Chroma (C) coming out of it, and buffer the Luma (Y) coming out of the VDP prior to sending both those signals through the FMS6400. I added notes to describe the functionality inherent in each area of the circuit.

 

 

On 9/19/2022 at 2:15 PM, Captain Cozmos said:

Rambo is the other option but is nothing more than extra ram which even my daughter when she was 11 could deign in KiCad.

Remind me to never doubt your daughter's abilities

 

 

On 9/19/2022 at 2:15 PM, Captain Cozmos said:

If I had to create a ram expansion board I would have it piggyback on top of the Z80 and remap the BIOS into that.  Plug and play, some bodge wire, cut a couple of traces.

I'm not looking to modify an existing CV console, but actually plan to build a miniaturized version that will be the size of this custom Atari I designed --- case design courtesy of @Mr Robot.

 

This is small, measuring 5.25 inches square, and 1-7/8 inches tall.

 

For the CV version, I'll be going with a top loading cartridge port, so that an AtariMax Ultimate SD Cart can get plugged in.

[Mr Robot]

2 hours ago, Captain Cozmos said:

By asking if it is possible, I would conclude that you have limited experience in electronics.

🤣 @mytek has limited experience in electronics in much the same way that Pacino is just starting out as an actor. 

[+DrVenkman]

2 hours ago, Captain Cozmos said:

By asking if it is possible, I would conclude that you have limited experience in electronics.

Aaaaahhh hahahahahahahaahahahahahahahahaahahahaahahahahaahahahahahahahah!!!!!!

 

Since you obviously have no idea who you’re talking to, Michael designed this, and this, and this, each one a complete bespoke implementation of an entire A8 computer from scratch, along with many other things big and small. He knows more about electronics design and building than probably 98% of people on this forum if not more.

 

[Captain Cozmos]

DrVenkman....
Mr. Robot....

It was not to pick a fight and I have no clue who the guy is or his accomplishments.

 

He asked a novice question and I addressed it as if answering a novice.

So did you want me to break out how to connect Address and Data lines to a Z80 cpu, buffers and everything?

If he invented those things in the pictures or just assembled from a kit one would conclude that he would already know the answer.
But that background was not established so again, I formed an answer geared toward the level of knowledge because I want everyone on Atari Age to achieve.

 

He found no offense when he responded but for some reason you guys did.

But hey, you had to prove some point so I guess you showed me.  yea..........

If helping an old lady across the street gets you berated then I just won't help old ladies cross the street.

Edited September 20, 2022 by Captain Cozmos

[+mytek]

Ok folks lets not get into a scrap about this. I never took any offense to what you said, but my peeps like Drvenkman were feeling the need to protect me. Please let's just sum it up to a general misunderstanding.

 

Now as for my question about substituting an 8Kx8 RAM for the two 1Kx4's that are normally used. I wasn't asking for how to do that, because I really do know what it would take, and as you pointed out it's pretty darn simple. What I was really wondering about... is having the 8K of RAM fully addressable instead of mirrored several times like the stock RAM, cause any potential conflicts with existing games?

 

And then the 2nd part was whether there would be any benefit to the extra 7K of RAM in that area?

 

Those two questions might make me look very inexperienced from a CV point of view, but really doesn't reflect upon my electronics abilities or experience in that particular area of concern. Can you see how those are two separate and unrelated things?

 

Anyway I'm glad we got that last part figured out

[Mr Robot]

41 minutes ago, Captain Cozmos said:

He found no offense when he responded but for some reason you guys did.

I didn’t take any offence I was just tres’ amused and offered up an example of just how far off the mark you were. It was meant light heartedly, I’m sorry if that wasn’t clear. 

[Falonn]

1 hour ago, mytek said:

Actually I have been experimenting on a real CV system, with the first order being to clean up the video (RF left the building, and in walks S-Video). Here's what I have done on that thus far...

It was very interesting when I stumbled on the idea to use the LM1889N modulator chip for only it's color encoder function. Then I just needed to appropriately amplify the Chroma (C) coming out of it, and buffer the Luma (Y) coming out of the VDP prior to sending both those signals through the FMS6400. I added notes to describe the functionality inherent in each area of the circuit.

That is a cool trick to use the same encoder that's already present to do most of the heavy lifting.  Nice idea!

 

For the Coleco RGB output board we worked on a couple years ago, it ended up taking a way more circuitous route.  (Granted, a direct VDP to Component version of that same board would get to drop more than half of that stuff--including the most expensive/overkill LMH1251 part.  The VDP's YUV output is almost YPbPr to begin with.  It just needs to be run through a quick level shift to get the colors right.)

[+mytek]

9 minutes ago, Falonn said:

That is a cool trick to use the same encoder that's already present to do most of the heavy lifting.  Nice idea!

Apparently I'm not the first, because a few days after I started my experiments I came across an article where someone else had essentially made the same discovery. However if I recall correctly there were some noise issues.

 

In my implementation I plan to get the 5VDC from a linear regulator being supplied by the 12VDC. This extra layer of voltage regulation and filtering caps really keeps things quite. I also use the FMS6400 in a 0 db gain mode, since the Luma level needs to be down rated anyway, and the slight amount of gain needed on the Chroma signal is minimal. End result is a very clean non-color bleeding picture, which actually looks quite nice via a RetroTink or similar if you want HDMI. The FMS also does a fantastic job of outputting a composite video signal as well, with out the possibility of it screwing with the S-Video side of things (the summing of the Y&C is done after first buffering those signals internally).

 

9 minutes ago, Falonn said:

For the Coleco RGB output board we worked on a couple years ago, it ended up taking a way more circuitous route.  (Granted, a direct VDP to Component version of that same board would get to drop more than half of that stuff--including the most expensive/overkill LMH1251 part.  The VDP's YUV output is almost YPbPr to begin with.  It just needs to be run through a quick level shift to get the colors right.)

I came across that exact same post and website last week when I was researching alternative video for the CV. Nice board and cool idea to make it installable from underneath the TMS chip (no desoldering of that chip required) 👍

[massiverobot]

If you are making a ColecNuc, consider making a whole ADAMuc? FujiNet is waiting as a daughtboard for your new ADAMuc.

[+mytek]

7 hours ago, massiverobot said:

If you are making a ColecNuc, consider making a whole ADAMuc? FujiNet is waiting as a daughtboard for your new ADAMuc.

Even though the current chip count is lower than the Atari version, and there are fewer large chips to deal with, the cartridge is going to eat up that space pretty quickly. I'm trying to keep the profile low like the non-cart version of the 576NUC+, so it will end up being a top loader instead of a side loading cartridge. The plan is to make it fit the existing case STLs, with only minor changes, and probably have the lid take on some of the look of a real CV.   EDIT: It'll be a low profile when there is no cart inserted -- making it good for transport.

 

However I've been looking at the RAM situation, and I believe it'll be pretty easy to mimic the Adam's 32K of RAM using a skinny DIP cache SRAM chip, and I might possibly be able to squeeze in the AY-3-8910 while I'm at it. But that's really going to get tight very quickly, so NO this won't be an Adam -- just an enhanced CV, a very tiny one at that. The AY-3-8910 chip and address decoding for it might even need to be on a small daughter board.

 

It looks like pretty soon I'll have to break this discussion off into its own topic

[+5-11under]

I think every game would work fine whether there was 8K RAM vs. 1K RAM mirrored 8x. The only time you would run into trouble is the non-likely case if you only had 1K non-mirrored, because some games use different mirrors, such as starting at $6000 vs. $7000. 

 

There's a couple of Team Pixelboy "Super" games such as Zaxxon, that use 24K RAM (or at least more than 1K), similar to the ADAM. These games don't need other SGM capabilities, and will work if you enable the RAM to fit the 24K "open" space. On the flipside, there's a few games that display "SGM required" and won't run if there's no SGM (even though they're probably not using the bottom 8K as RAM, and the extra sound might not be required to effectively play the game). Most of Pixelboy's games are available for free download, so you can test these out.

[Pixelboy]

41 minutes ago, 5-11under said:

I think every game would work fine whether there was 8K RAM vs. 1K RAM mirrored 8x. The only time you would run into trouble is the non-likely case if you only had 1K non-mirrored, because some games use different mirrors, such as starting at $6000 vs. $7000. 

I believe Super Cobra is the only actual example of this, and it doesn't run properly on the ADAM because of the non-mirroring RAM setup. nanochess made a fixed version of that game ROM some time ago.

 

nanochess also fixed Defender, if I remember correctly, but I'm not sure if this was a ROM issue or a NTSC/PAL issue.

 

[+mytek]

3 hours ago, 5-11under said:

There's a couple of Team Pixelboy "Super" games such as Zaxxon, that use 24K RAM (or at least more than 1K), similar to the ADAM. These games don't need other SGM capabilities, and will work if you enable the RAM to fit the 24K "open" space. On the flipside, there's a few games that display "SGM required" and won't run if there's no SGM (even though they're probably not using the bottom 8K as RAM, and the extra sound might not be required to effectively play the game).

 

Thanks for the good info.

 

Here's what I've come up with for enabling a 32Kx8 SRAM chip to take the place of the original two 2114 rams (only accessing 24K of it).

 

 

I still have one more chip select for the missing 8K, and I'm curious as to how that first 8K ($0000-$1FFF) gets accessed. From what I've read elsewhere, it appears that there is a swap of this space between RAM and ROM (BIOS), but I'm not all together sure how that is done, or should I say decoded.

[+5-11under]

The SGM has a latch for the ROM vs. RAM for bottom 8K. I  haven't looked up the details on that in the SGM, but I think it's just latched by hitting a memory hotspot.

 

If you look at the schematic for the ColecoVision (by the way, the popular schematic has some errors in the clock section, unless they've been repaired in newer versions), you'll see the '138 Y0 goes to the ROM chip. However, the SGM, being external, can control the '138 via the EX_DEC_EN leading to G1 on the '138. Send that signal to ground whenever you don't want to use the standard memory map.

[chart45]

[+mytek]

8 minutes ago, 5-11under said:

If you look at the schematic for the ColecoVision (by the way, the popular schematic has some errors in the clock section, unless they've been repaired in newer versions), you'll see the '138 Y0 goes to the ROM chip.

I've been using ChildofCV's schematics for reference. Is this the one that you are referring to that might have some errors?

 

13 minutes ago, 5-11under said:

The SGM has a latch for the ROM vs. RAM for bottom 8K. I  haven't looked up the details on that in the SGM, but I think it's just latched by hitting a memory hotspot.

Looks like @chart45 just helped me out with a schematic (thanks). It looks like I should probably use a PLD instead of the discrete 7400 series chips (that's a lot of chips). However at least now I know what's required.

 

I just realized that schematic also includes the AY sound chip interface as well -- so complete SGM?

 

Thanks to all

 

[+5-11under]

I was referring to some older schematics... ones that are > 10 years old.

[chart45]

took me almost 10 years 🤣

 

 

[+mytek]

19 minutes ago, 5-11under said:

I was referring to some older schematics... ones that are > 10 years old.

Got it 👍

 

18 minutes ago, chart45 said:

took me almost 10 years 🤣

 

 

Thanks for saving me years that I no longer have to squander (I'm going to be turning 67 in February)

 

I've always wanted to learn how to code for a PLD, so this looks like a great opportunity to do so. Having your known to be working schematic will go a long ways towards having a fruitful outcome in that endeavor. If my efforts are successful I'll be sure to share the JED files and a schematic.

[chart45]

4 minutes ago, mytek said:

Got it 👍

 

Thanks for saving me years that I no longer have to squander (I'm going to be turning 67 in February)

 

I've always wanted to learn how to code for a PLD, so this looks like a great opportunity to do so. Having your known to be working schematic will go a long ways towards having a fruitful outcome in that endeavor. If my efforts are successful I'll be sure to share the JED files and a schematic.

i always share my stuff cause im doing it for fun and learning.. i made it to build a megacart with a gal and wincupl.. also with xilinx with the schematic tool.. not so great but i dont know vhdl so its next on my list.. pretty hard with kids and stuff