800XL user-installed switch...

[Mrarkus]

I just acquired an 800XL with a Newell 256K RAM upgrade. It has two SPDT switches on top - one I figured out is a switch between Newell/Rambo mode for the upgrade. The other however I'm not sure what it is for:

 

Center connected to Halt on Newell board

One side connected to a cap by power connector via a resistor

Other side connected to Antic Pin 9 (HALT signal)

 

Any idea what this switch does?

[+Nezgar]

"Switch between newell/rambo mode" is a bit ambiguous - is that switching the bits used for bank selection?  I believe Newell RAM upgrades had extra logic to prevent shadowing of the main 64K as 4 extended banks, whereas the simpler Claus Buchholz/ICD Rambo/Wiztronics 256K upgrades did not.

 

Maybe a picture would help?

[+Nezgar]

The switch maybe a switch between 130XE style 128KB "ANTIC" and 256KB "non-ANTIC" banking modes according to this post about the Newell board:

 

https://atariage.com/forums/topic/267985-newell-industries-256kb-xl-ram-issues/

 

[BobJones]

I seem to remember some ram upgraded with a switch where you could load a disk into a portion of ram , flip the switch, reset and boot the machine and use the ram upgrade as a super fast second drive. Works well with spell check software. But I could be wrong.

Sent from my Pixel 4 XL using Tapatalk

[Mrarkus]

24 minutes ago, Nezgar said:

"Switch between newell/rambo mode" is a bit ambiguous - is that switching the bits used for bank selection?  I believe Newell RAM upgrades had extra logic to prevent shadowing of the main 64K as 4 extended banks, whereas the simpler Claus Buchholz/ICD Rambo/Wiztronics 256K upgrades did not.

 

Maybe a picture would help?

 

I found this article: https://www.atarimax.com/freenet/freenet_material/12.AtariLibrary/2.MiscellaneousTextFiles/showarticle.php?105 which matches what the first switch is and how it's connected. Here is a quote:

 

    This modification will make a Newell 256K Atari 800XL compatible with,
the PD "130XE compatible" 800XL 256K project, as well as the RamboXL 256K kit
for the 800/1200 XL's. In other words, Make Your Newell 256K 800XL compatible
with Most of the other 800/1200 XL and 130XE Mods.
 
    The problem is a simple one. It seems the difference is in how the
different modifications use Bit 5 off of the PIA chip. All you need to do is
provide a way to invert this one signal in the Newell upgrade and it will
operate like the Public Domain and RamboXL upgrades with all the excellent
error checking the Newell 256K Provides. If you also provide a way to switch
it back, it will act like the Newell again, Thus giving you the Best of Both
Worlds.

My concern is the second switch, which I can't find any info on. 

Edited October 4, 2020 by Mrarkus

[TGB1718]

1 hour ago, Mrarkus said:

My concern is the second switch, which I can't find any info on. 

Photo's inside and out would help us identify

[Mrarkus]

OK, here we go, some pictures....

[Mrarkus]

I am going to give it one bump to see if anyone wants to take a stab at it...

[TGB1718]

Still not sure of it's function, but with the switch in one direction it just puts a pullup to +5V to the Newell HALT.

 

In the other position it allows ANTIC to send the HALT signal to the Newell board, probably allowing ANTIC to

refresh the RAM

[ClausB]

HALT is used in the 130XE to determine whether ANTIC or SALLY is accessing RAM. So the switch defeats that separate ANTIC RAM access mode which the "PD" upgrade doesn't support (shame on the designer! ).

[+Nezgar]

So in a "Rambo/PD style" 320KB (256KB extended) computer, allowing separate antic banking reduces accessible extended RAM to 192KB.

 

In a 256K machine, would this reduce accessible extended RAM since there was already only 192KB? If not, yeah - there's a grand total of what - 5 known titles that use separate antic banking? The effort to install the switch would then be of questionable value, but articles of the day made a big deal out of it...

[Mrarkus]

Ok, that makes more sense now, thanks!