RAM 512KSRAM extension module for Atari 65/130XE

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pancio
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RAM 512KSRAM extension module for Atari 65/130XE

Postby pancio » 11 May 2019, 21:12 - Sat

This article will show how to build, assembly and use the SRAM 512KB memory extension, This is my own modification based on Matthias Reichl aka Hias SRAM v1.3 from https://www.horus.com/~hias/atari/#sram512k page. It's my adaptation and it's prepared for some 65XE and 130Xe Atari computers. You may follow the discussion with topic (Polish) on http://www.atari.org.pl/forum/viewtopic.php?id=15938 regarding any doubt, issues and solutions.

Why?
Well, on the market you may find so many Ram extension for your Atari but...
- this one is Static RAM (less power consumption)
- only 3 wires are necessary (if you have socketed CPU, PIA and MMU)
- RAMDISK feature after power off the Atari.
- very cheap RAM


Let's start.
Matthias didn't publish any PCB so I had little much work to do. At first I rearranged schematic in order to use piggy style assembly - I decided to use CPU as a base with full data and addresses buses. Additional I decided to place CPU and PIA on the same PCB as piggy. It's possible that in 65XEN both ICs are closer together. So, the schematic contains two piggys:
sram13v5.png
SRAM 512k schematic
sram13v5.png (47.63 KiB) Viewed 810 times
Prototyping and Manufacturing
This mod is my first which I made with KiCAD. I can't work anymore with Autodesk Eagle because of it's limitations (PCB size, price). The KiCAD is so powerful as well. Matthias provided his project with Eagle format but KiCAD has very good import tool. Of course some corrections were necessary with used part on schematic. When I rearranged all wires I made a few prototypes on paper in order to match to Atari's motherboard.
sram13v5pcbpaper.jpg
SRAM 512k paper prototype
After a few trials the PCB was done:
sram13v5pcb.png
SRAM 512k PCB KiCAD
sram13v5pcb3d.png
SRAM 512k PCB KiCAD 3D
Well, regarding PCB manufacturing I may say only: never expect so much. On Polish market we have many PCB supplier but the price is rather terrible. I tried many China market company with rather good result for best price. This time I chosen JLCPCB because they have very good price with so short delivery time! (4 days! for production and delivery).

That's result:
sram13v5pcb-clean.jpg
SRAM 512k PCB RED
The quality is very good so I will recommend this company for prototyping process

Assembling

At first I burned GAL chip with new logical matrix from JEDEC file from Matthias's page:
XGPRO.png
XGPRO GAL22V10 programming
Next step is necessary if you have not socket ICs. In my case I desoldered CPU, PIA and small MMU and socketed. Pin 6 and 16 of MMU should be cambered to up and soldered to wired on memory board. The same with 16 pad of MMU socket (see schematic):
sram13v5motherboard_prepared.jpg
Atari 65/130XE socketed and prepared for extension

then assembly all on extension board:
sram13v5board.jpg
SRAM 512k PCB assembled
and finally result:
,
sram13v5motherboard_mounted.jpg
SRAM 512k on motherboard. Final result
Test
It was terrible... you may find some details on http://www.atari.org.pl/forum/viewtopic.php?id=15938
I thought that something is wrong with extension because demo Videoblitz doesn't work properly...

Well, many hours testing, colleagues suggestions from http://www.atari.org.pl/forum ... and the final result was found...
tbd...

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