An unusual 520 STF

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highway
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An unusual 520 STF

Post by highway »

Hi all

I just got a 520 STF. As I had a 1040 STF when I were young, i wanted to go back in past !

The 520 STF I got was given for a 1040 due to ram boost.
It'a a very first version of STF, has it had a single sided floppy disk and both LED were red.
I adapted a PC floppy drive, and started it : it's alive !

When I opened it, i saw a mod with SIMM memory module. I've been a bit surprised as for me only STE had this feature.
Image

Afterthat I checked the available of RAM in GEM, and i've allmost 3.7 Mb available

Is that a module that was available in the market ?
Did you often saw 4Mb STF ?
Do I have an ovni ?

thanks in advance
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paul92706
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Re: An unusual 520 STF

Post by paul92706 »

Very nice!, i wonder if thats a MMU chip to the bottom left? :)
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Arne
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Re: An unusual 520 STF

Post by Arne »

paul92706 wrote:Very nice!, i wonder if thats a MMU chip to the bottom left? :)
On that additional PCB? That's a Shifter for sure.
That's probably a "home-made" PCB SIMM memory expansion board. I've done something similar for four SIMMs myself 20 years ago.
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Re: An unusual 520 STF

Post by paul92706 »

Arne wrote:
paul92706 wrote:Very nice!, i wonder if thats a MMU chip to the bottom left? :)
On that additional PCB? That's a Shifter for sure.
That's probably a "home-made" PCB SIMM memory expansion board. I've done something similar for four SIMMs myself 20 years ago.
ah! right the MMU is already intergrated to the motherboard, makes sense, those bits need to be shifted. Ya it looks homemade, great job who ever did that mod :)
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highway
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Re: An unusual 520 STF

Post by highway »

I confirm, this chip is a shifter. It is even the original one, as it is directly strapped to the base below.
Reference is C025914-38A

My TOS seems to be stored in 6 chips under the PSU, with the reference C026329 (30/31/32/33/34) - 002
Is that possible to know with TOS it has ? (I do not have rainbow TOS ... and still not the capacity to transfer from PC to Atari, so I can't try a sysinfo like.
Is it possible to find a 1.04 TOS for this kind of chips ?

thanks in advance
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Re: An unusual 520 STF

Post by highway »

Hello
Could anyone explain to me the difference between the shifter and the mmu ?

In order to install a swtich to toggle 1Mb to 4Mb, i need to find A9 on the mmu...
I thougt i would have the mmu near to the ram, but this seems to be the shifter...
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Re: An unusual 520 STF

Post by exxos »

MMU = Memory Management Unit.

The shifter is what generates the video.

A lot of Ram upgrades plug over the shifter as a lot of signals are present there, so its easy to take them from the shifter as its the only easy accessible place. You can just find A9 on the simms and follow that line to the MMU. Probably be easier to isolate the line there anyway.
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Re: An unusual 520 STF

Post by Zogging Hell »

highway wrote: My TOS seems to be stored in 6 chips under the PSU, with the reference C026329 (30/31/32/33/34) - 002
Is that possible to know with TOS it has ? (I do not have rainbow TOS ... and still not the capacity to transfer from PC to Atari, so I can't try a sysinfo like.
Is it possible to find a 1.04 TOS for this kind of chips ?

thanks in advance
Just check the date in desktop info. 1985 = TOS 1.0, 1987 = TOS 1.02, 1989 = TOS 1.04.
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Re: An unusual 520 STF

Post by highway »

I just added a switch today to toggle between 1 and 4 Mo.
It works fine and some games that didn t worked can be used now!
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