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jrhodes

Internal memory mod

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Starting this thread as a place to discuss systems with the internal memory mod, and questions or issues associated with this setup.

Feel free to ask your internal memory mod related questions here.

 

First question:

Can this mod be installed with a toggle switch, to turn off the internal memory mod if wanted?

 

Second question:

Can a SAMS setup be installed internally?

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Can an EA + 4 banks switcheable be installed? Obviously, the battery should also be run outside the case OR be a rechargeable type, but I don't think there's a circuit for recharging these.

 

Edited by GDMike

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3 hours ago, jrhodes said:

Starting this thread as a place to discuss systems with the internal memory mod, and questions or issues associated with this setup.

"the internal memory mod" or "an internal memory mod" - did you have a particular one in mind as there are several (assuming you're referring to 32K in the console)?

 

The one I put together (http://www.stuartconner.me.uk/ti/ti.htm#32k_memory_expansion) has a switch to disable it. It's probably possible with any of the 32K mods, although you might need to tweak the mod circuit slightly to fit it.

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13 minutes ago, Stuart said:

"the internal memory mod" or "an internal memory mod" - did you have a particular one in mind as there are several (assuming you're referring to 32K in the console)?

 

The one I put together (http://www.stuartconner.me.uk/ti/ti.htm#32k_memory_expansion) has a switch to disable it. It's probably possible with any of the 32K mods, although you might need to tweak the mod circuit slightly to fit it.

I intended this thread as a catch all for all different versions.

Since you say your version can definitely have a switch installed, that is the one i would do, if i ever did it.

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Several of the 32K-in-the-console mods have on-off switches, and some are also able to switch speeds (using two different clock crystals), and may be able to switch between 16-bit and 8-bit memory modes. I'm pretty sure Mainbyte, Hexbus, Tursi, and Stuart all have nice options detailed on their sites. There are also a couple of innovative threads here on AtariAge.

 

There is not an option available to put SAMS into the console.

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My internal 32k mod as designed doesn't have a switch. The PCB for mine that someone else (Towmater?) designed, DOES.

 

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1 hour ago, Tursi said:

My internal 32k mod as designed doesn't have a switch. The PCB for mine that someone else (Towmater?) designed, DOES.

 

@Tursi I think this is your circuit with the switch I believe, correct?

 

32kmod.jpg

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5 hours ago, Shift838 said:

@Tursi I think this is your circuit with the switch I believe, correct?

 

 

32kmod.jpg

That looks familiar, but I wasn't really involved in the development of it and have never seen one in person ;)

 

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The one I have adds 64 K RAM in the console. It's all at 16 bit wide bus. Thus you can have your workspace anywhere. It's as fast as console RAM pad anyway.

The 32 K covering the area for the normal memory expansion is on by default. If switched off, any external memory expansion (in the PEB) will be visible instead. So by switching off the internal memory, you go back to 8-bit speed, but also has a second page of 32 K RAM.

The remaining 32 K RAM in the console can be switched on in 8 K banks. Thus you can overlay all other areas in the console with RAM. This includes console ROM, DSR space etc.

Of course, you can't return to a normally operating machine with memory and all VDP ports and stuff at >8000 - >9FFF replaced with RAM. You'll crash immediately. But inside your own program, your can turn on that bank and use it as some buffer memory, or whatever, as long as you disable it before returning to the console. Another options is to transfer a part of your program to that area. Then, when your assembly program is called, you can enable that area, run your program there, jump back to your program elsewhere and disable the memory before you return. This means you can have space for up to 32 K of software, in your own assembly program, which is all loaded and can be accessed by just a toggling of some CRU bits.

You can also copy all console ROM to RAM, then switch in the RAM. Now you can modify all interrupt vectors and such stuff. You can for example use the timer in the TMS 9901 to create an interrupt to a scheduler, if you want to run a multitasking assembly program with pre-emptive task switching.

Another possibility is to have a contiguous 64 K RAM area in the machine, if you temporarily need to manage a lot of data.

These different banks are all switched in and out by CRU bits at >0400, so all this can be done under software control.

 

This is my own design. I never made any PCB, though, so it's all soldered in piggy-back on existing circuits in the console.

I've also never used a Commodore 64 in any depth, but I do know it had a similar capability. It could be 64 K RAM, but not at the same time as having access to all system services.

Edited by apersson850
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Although I posted it already in another thread, once again this is the mod I used with my TI-99/4A before switching to the Geneve.

 

The red and yellow buttons do not belong to the expansion but are used for resetting and triggering the LOAD interrupt. The switch turns off the wait state generation when accessing the 32K memory.

 

I seem to vaguely remember that this could be from the Wiesbaden group and that they offered to install it if you sent the mainboard to them.

Int32k.jpg

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Dutch magazine has articles how to built in 32K

 

Tijdingen 23  october 85

Tijdingen 24 december 85

 

(There might be more in others, but need to search)

20210902_225339.jpg

20210902_225359.jpg

20210902_225611.jpg

20210902_225557.jpg

20210902_225552.jpg

20210902_225546.jpg

20210902_225535.jpg

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I got the basic idea to my design from somebody who installed 64 K RAM, but only used half of it. The reason for installing 64 K was simply that the memory chips were 8 bit wide. So that design used 16 K from each 32 K chip, to get a 16 bit wide memory data bus.

Seeing that, I thought I could improve on the design by adding the logic which would allow the use of all of the memory in the chips.

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But with a single chip like that, you don't get 16 bit wide access, right?

You get the memory but not the speed upgrade, as far as I understand.

Edited by apersson850

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Yes I see your point it's only a 32k 8bit mod.
I suppose if anyone is going to make the effort to do a mod, 16bit is the way to go.

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I don't intend to ever install another 16-bit mod. I developed my 8 bit mod because it was fewer wires to solder. ;)

 

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That's the advantage.

When running programs where both the code and the workspace is in expansion RAM, the speed increase with 16-bit access is roughly 110%. I found that signifcant enough to do the job with installing the 16-bit memory. And then some, since I actually added 64 K RAM to the existing 32 K RAM upgrade, not just replaced the standard memory expansion.

Edited by apersson850
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I know, we've discussed your memory mod a couple of times before. :)

 

I also upgraded my daily use console back in the day, then used it to run a BBS where the extra speed helped it keep up with the modem as well as granted me faster build times.

 

But these days, my TI is not my daily use console and I'm more interested in making sure my software will run the same way that it will run on most people's machines.

 

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