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A little bit of 8 Bit: 65XE upgrade to 128k RAM

Posted: Thu Aug 31, 2017 12:40 am
by rubber_jonnie
Hoping nobody minds, especially since we are predominantly 16 Bit, but having just completed a successful upgrade of my 65XE from 64k to 128k, I know how difficult it was to source the parts, so I wanted to share with everybody.

The parts needed are:

1x 20 pin DIL socket for the MMU chip
8x 16 pin DIL socket for the RAM chips
8x 1uF ceramic capacitors
1x Atari C25953 MMU (Search eBay for "NEW Atari computer 16 DIP IC 130XE 65XE 65 130 XE C25953-20 EMMU memory IC chip")
8x RAM chips (Search eBay for "8x MB8264A-15, 64Kx1-bit NMOS Dynamic RAM-NEW", a guy in Bulgaria is selling and has some left)

Your 65XE will need to be one that has the slots free for the additional memory, or this won't work.

IMG_20170807_213028.jpg
First off prep the board. Where the socket is marked U34, there are 3 zero ohm resistor/links. These will need to be removed.
IMG_20170807_213028.jpg (3.74 MiB) Viewed 5915 times
IMG_20170809_214647.jpg
Once the 3 zero ohm resistors are removed, use solder wick to clean up all of the holes.
IMG_20170809_214647.jpg (4.47 MiB) Viewed 5915 times
IMG_20170809_220209.jpg
Solder in all the capacitors, followed by the 8x 16 pin sockets in slots U26 to U33, and the 1x 20 pin socket in the slot marked U34.
IMG_20170809_220209.jpg (4.31 MiB) Viewed 5915 times
IMG_20170809_223335.jpg
Finally, plug in all of the RAM chips into U26 to U33, and the C25953 MMU into U34. Make sure the C25953 is located to the left of the 20 pin socket when looking from the front of the mainboard, and as in the picture.
IMG_20170809_223335.jpg (4.07 MiB) Viewed 5915 times
Once completed, find a 128k demo, such as the Space Harrier Demo (This is really cool!), and if everything is ok, then your 128k software will run.

Mine worked first time, but if it doesn't work for you, I suggest a magnifying glass to make sure there are no solder whiskers bridging pads, and that all the chips are nicely seated.

If it doesn't work first time, provided you've used sockets, then you can remove the chips and check it's all good without.

Re: A little bit of 8 Bit: 65XE upgrade to 128k RAM

Posted: Thu Aug 31, 2017 12:26 pm
by tfhh
Hi,
rubber_jonnie wrote:
Thu Aug 31, 2017 12:40 am
Hoping nobody minds, especially since we are predominantly 16 Bit, but having just completed a successful upgrade of my 65XE from 64k to 128k, I know how difficult it was to source the parts, I wanted to share with everybody.
Nice solution - well done! :goodpost:

If you want... I make another solution - cheaper and same effort, but you will get 320 KB RAM :)

You need:
8x 41256 DRAMs
1x resistor 33 Ohm
1x GAL 16V8 DIP
1x 74LS95

Insert the 8 DRAMs (you can get them cheap on eBay or you buy an Amiga 500 memory expansion for less then 10 USD/Pound/Euros which contains such DRAMs often and rip off the chips). Bent pin 1´s of the 8 DRAMs up OR connect unused pads for pin 1 of the sockets. You don´t need the CO25953, the GAL will do this job.

img6F.jpg
img6F.jpg (857.22 KiB) Viewed 5903 times

Here´s the GAL source listing:

Code: Select all

CHIP    XE_320k    GAL16V8    SIMPLE_MODE

A14    A15   pb2   pb3      pb4      cas     pb6    pb7  mode  GND
mhalt  ra8   map   casbank  casmain  fa_14   fa_15  pb5  phi2  VCC

 fa_15        = A15
              + A14 & pb3 & /pb4 & mode & mhalt
              + A14 & pb3 & /pb5 & mode & /mhalt;

 /fa_14       = /A14
              + /A15 & /pb2 & /pb4 & mode & mhalt
              + /A15 & /pb2 & /pb5 & mode & /mhalt;

 casmain      = /phi2
              + cas
              + /A15 & A14 & /pb4 & mode & mhalt
              + /A15 & A14 & /pb5 & mode & /mhalt;

 /casbank     = /A15 & A14 & phi2 & /pb4 & /cas & mode & mhalt
              + /A15 & A14 & phi2 & /pb5 & /cas & mode & /mhalt;

 /map         = pb4 & pb5 & /pb7;

 ra8          = /phi2 & pb6 & mode
              + phi2 & pb7 & mode;
The LS7495 must be placed at the positon of U35. The GAL - bent pin 7, 8, 9,12 and 13 up - will be placed in U34. Connect pin 7 of the GAL to pin 16 of PIA and pin 8 of the GAL to pin 17 of PIA. Pin 9 can be left open (expansion enabled) or closed by switch to ground to disabled the expansion. Pin 12 via 33 Ohm resistor to the pin 1´s of the 8 DRAMs (memory addressline A8) and pin 13 to the pin 6 of MMU. This pin must be also bended, so better is to desolder the MMU, fit it into a socket and replace it with pin 6 bend up.

I make several years ago an article for the ABBUC magazine no. 95. You can download it here, but the text is only in german - sorry.

Jurgen

Re: A little bit of 8 Bit: 65XE upgrade to 128k RAM

Posted: Thu Aug 31, 2017 4:07 pm
by rubber_jonnie
Cool, nice one :D

A little more complex to do, but very nice result.

Re: A little bit of 8 Bit: 65XE upgrade to 128k RAM

Posted: Thu Aug 31, 2017 4:46 pm
by exxos
Well done to both :bravo:

Re: A little bit of 8 Bit: 65XE upgrade to 128k RAM

Posted: Mon Sep 04, 2017 5:22 pm
by rubber_jonnie
Here is the finished article, reassembled post 128k upgrade and with a case and keyboard clean.

Looking good for over 30 years old.
IMG_20170904_165253.jpg
Reassembled and cleaned.
IMG_20170904_165253.jpg (3.5 MiB) Viewed 5883 times

Re: A little bit of 8 Bit: 65XE upgrade to 128k RAM

Posted: Mon Sep 04, 2017 5:40 pm
by exxos
rubber_jonnie wrote:
Mon Sep 04, 2017 5:22 pm
Here is the finished article, reassembled post 128k upgrade and with a case and keyboard clean.

Looking good for over 30 years old.
*envy mode on*

Re: A little bit of 8 Bit: 65XE upgrade to 128k RAM

Posted: Fri Feb 23, 2018 6:30 pm
by redhawk668
I’ve done a 320 kb upgrade on a 130XE, I had to desolder the second bank of ram chips. My solution uses a 74LS158, a 33 ohm resistor and some wire. I used the 256 kb drams from a dead Atari ST.

Re: A little bit of 8 Bit: 65XE upgrade to 128k RAM

Posted: Sat Feb 24, 2018 6:39 am
by atari030
Nice to see some 130XE love. Mine is sitting between a A1200 and a Falcon and I have one more to fix. When I got my 800XL the 130XE popped along not long after and I would go all giddy looking at photos of it, same as I did for the Falcon. Say what you will, Jack Tramiel new styling.

Re: A little bit of 8 Bit: 65XE upgrade to 128k RAM

Posted: Sat Feb 24, 2018 10:49 am
by rubber_jonnie
redhawk668 wrote:
Fri Feb 23, 2018 6:30 pm
I’ve done a 320 kb upgrade on a 130XE, I had to desolder the second bank of ram chips. My solution uses a 74LS158, a 33 ohm resistor and some wire. I used the 256 kb drams from a dead Atari ST.
Any chance of some pics and details?

Re: A little bit of 8 Bit: 65XE upgrade to 128k RAM

Posted: Thu Mar 22, 2018 2:20 am
by walter_j64bit
A 65XE to 128k nice work! I would love to see 65XE to 256K. 8-)