4-bit 65XE RAM upgrade

[+slx]

I got a PAL 65XE with a 130XE motherboard with 4-bit-RAM, i.e. two empty RAM positions. Sorry if this has already been posted here but I can't seem to find instructions on how to upgrade this to 130XE standard (or 256K). Any pointers?

 

Thanks!

[Mathy]

Hello slx

 

It's not that hard. IIRC, you just need to solder in the two extra RAMs (or better yet, solder in two sockets and place the RAM chips in the sockets). Then remove (desolder) the resistors/jumpers (all three of them) from where it says "U34". Solder in a socket and put the CO25953 (Best Electronics or B&C Computervisions) in it. But take care, there are enough holes in the PCB for a 20 pin socket, but the CO25953 only as 16 pins. You need to put the CO25953 as far left as possible, so the holes you do not need are at the right of the chip.

 

Sincerely

 

Mathy

[MEtalGuy66]

Yeah.. And if you plan to go past 128k, you might as well not waste your time putting those 64kx4 ram chips in, because youll just end up taking them back out anywayze. The 256kx4bit chips are a completely different pin-out, so you cant use them on the same footprint as(or piggybacked on) the 64kx4..

 

So.. You could wire in a small perfboard with a 30pin SIMM socket (and your upgrade logic of choice.. Petersen, Compyshop, Mathy, etc.)

 

But what you SHOULD do is forget about all that crap.. And just do this instead:

 

http://www.horus.com/~hias/atari/#sram512k

 

It costs you a single 512kx8 DIP package SRAM, and a GAL22v10.. (about $12-$15US from Jameco).

 

You piggyback the SRAM on top of the OS rom, and hook up about 12 connections to the GAL..

 

You get true 130xe compatability (separate ANTIC/CPU access to extended ram) and if you install switches (a few extra conections) you can switch between memory configs ranging from 64k-128k-320k-576k... You can optionally install a 3v battery to make the extended ram non-volatile.. And even install QMEG OS which lets you boot from the ramdisk.

 

No need to buy or install U34.. Leave it the way it is.. No need to install 64kx8 DRAM chips..

 

And the machine will run more stable because there will be less load on the data bus than if you had done the upgrade with DRAMs.

[Marius]

Metalguy is right. I built a few of these in several Atari computers and it is a VERY STABLE upgrade.

 

I soldered the wires and components to a small hobby print board in stead of everything direct on the pia and the new Gal,

 

I also soldered a socket on the Os rom in stead of the SRAM directly soldered.

 

It's really cool.