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Replacing the 130XE MMU amd EMMU with GAL chips


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#1 morelenmir OFFLINE  

morelenmir

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Posted Thu Aug 9, 2018 3:20 PM

I notice an old post which mentions it is possible to replace the MMU with a 16V8 GAL:

 

MMU Chip Needed

 

I have a couple of LATTICE GAL16V8D15LP chips handy. Would these do the job when programmed with the TL866A?

 

Also, is it just a case of swapping out the MMU and directly plugging in the GAL?

 

I ask because, doing the same with the EMMU seems to be possible as well:

 

https://www.atarimax...rg/achemmu.html

 

However in that case it appears rather more convoluted, requiring the population of an empty header with a 74LS95/74F95 as well as shorting leg 15 of the GAL to ground.

 

For the sake of reference, this is the JEDEC proposed for the MMU:

 

Attached File  mmupal.jed   3.12KB   7 downloads

 

and this for the EMMU:

 

Attached File  co25953-gal.jed   2.91KB   6 downloads


Edited by morelenmir, Thu Aug 9, 2018 3:24 PM.


#2 Mathy OFFLINE  

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Posted Thu Aug 9, 2018 5:51 PM

Hello morelenmir

 

Jindroush found that information here on my Special Stuff Page.  After studying the schematics for the gazillionth time years ago, I concluded that U35 was a 74LS95B.  This was tested by Guus Assmann and Christopher Lang and confirmed.  And I'm under the impression that the information in the JDEC file (which was put together by Chris) for the CO25953 has since been used for quite a few memory expansions.

 

Sincerely

 

Mathy



#3 morelenmir OFFLINE  

morelenmir

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Posted Thu Aug 9, 2018 7:19 PM

That sounds pretty straightforward then--the GAL-for-MMU is a direct swap followed by a slightly more complicated GAL+LS95-for-EMMU.

 

I will start out with the MMU first and then try the EMMU.



#4 xrbrevin OFFLINE  

xrbrevin

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Posted Fri Aug 10, 2018 11:10 AM

i found that burning an MMU was cost-effective but for the EMMU mod, it is cheaper to just buy a genuine one off ebay UK

 

https://www.ebay.co....CoAAOSwCM5XPuiI



#5 morelenmir OFFLINE  

morelenmir

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Posted Sat Aug 11, 2018 12:07 PM

i found that burning an MMU was cost-effective but for the EMMU mod, it is cheaper to just buy a genuine one off ebay UK

 

https://www.ebay.co....CoAAOSwCM5XPuiI

 

Ah, but then you miss out on all the fun of the chase!!!  Seriously though, I can 100% confirm that the MMU JED and swap with a GAL16v8 works completely.

 

I have not done the EMMU yet because I am still waiting for the 74-series logic IC to arrive.



#6 1050 OFFLINE  

1050

    Dragonstomper

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Posted Mon Aug 13, 2018 10:31 AM

Except you haven't fully tested it yet grasshopper...

I thought so too, until I started a complex printing
project and where I have done it before and knew it
like the back of my hand, it would not start with the
GAL MMU in place. Suspicious, this might be the issue
a swap showed it was the case and the printing began.

They do work is the take away, but there can be timing
issues even with the best effort to match original and
exactly why my GAL failed to function in only this
mode is beyond my capabilities to find out about.
Just because it doesn't immediately take you to the
self test doesn't mean all is perfect. Wish I had a
conclusion to this story too but I don't.

#7 morelenmir OFFLINE  

morelenmir

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Posted Mon Aug 13, 2018 1:40 PM

Except you haven't fully tested it yet grasshopper...

I thought so too, until I started a complex printing
project and where I have done it before and knew it
like the back of my hand, it would not start with the
GAL MMU in place. Suspicious, this might be the issue
a swap showed it was the case and the printing began.

They do work is the take away, but there can be timing
issues even with the best effort to match original and
exactly why my GAL failed to function in only this
mode is beyond my capabilities to find out about.
Just because it doesn't immediately take you to the
self test doesn't mean all is perfect. Wish I had a
conclusion to this story too but I don't.

 

An excellent point!!! I only have an SIO2SD-USB to attempt printing through, but I will give it a shot.

 

My motivation to swap out the stock MMU was to potentially remove a source of graphical artefacting. Sadly, while--appearing--to work properly the GAL made no difference to the display so I will probably switch back to the original part before long anyway.






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