Jump to content

Reverse Engineering the Macintosh SE PCB & Custom Chips for 1:1 reproduction


Recommended Posts

@quorten Looks like you've got quite a bit of stuff there. I've got a copy of VCS, so I'll get it up and running there. I owe Synopsys a SNUG paper for loaning it to me, so maybe this might end up there. I'll take a look and see what I can gather. I immediately focused on one of your points, in that if we chose to implement this in an FPGA, we should probably make a daughter card and put on memory. It would cost peanuts to put down all the memory the MAC could use, probably in a single chip :) 

 

This looks like it could be fun.

Link to post
Share on other sites
  • Replies 689
  • Created
  • Last Reply

Top Posters In This Topic

@ScutBoy Seems like you had everyone worried it would be lost, ha!  Thanks again for snatching that up.  I really only need some high-res photos of the PCB.  I really hope that it is through hole and without anything too advanced on the PDS card itself.  If it is through hole, reverse engineering will be easy.  If it has more than a few SMD and 4+ layers it will be beyond my skills and I'll have to send it out.

 

For completeness sake here is a discussion about the Mac SE Brainstorm.  I love that, unlike most accelerators, it actually speeds up the bus.  To me that makes it better than a 68020 or 68030 (at lower speeds) since there is still a bottleneck. 

Screen Shot 2020-12-31 at 3.24.51 PM.png

Link to post
Share on other sites

@maceffects they'll never use all 4mb - they'll read as 1MB SIMM's (as the needed address lines aren't connected at all.) - You also don't have to install the 3rd parity chip either. Seem to be working great in other systems of the vintage. Can't see why they wouldn't work for that - but even if not...well i now have enough SE/30 boards to get going :D

Link to post
Share on other sites
3 hours ago, Kai Robinson said:

BTW - anyone invested in this project such as @techknight, @maceffects, @quorten, @asicsolutions, @cheesestraws and anyone who has been sent a rev 1.4c board - please join the Retro Tinkering Discord: https://discord.gg/8dJxmF8Tzh - easier to chat in there about things to save this thread from getting too cluttered! :)

 

Seems like its more Amiga than anything else. Amiga really isnt my thing. 

Link to post
Share on other sites

Is anyone familiar with the bootloading process following reset? The 68000 data sheet shows going to address 0 following reset, which is RAM, but ROM, which presumably is where the loader resides, starts at 0x40,000.  

 

And Kai, most of the 68K signals are available on the PDS slot, so populating the desired pin sockets with a hand full of square post pins should provide a good connection point for the LSA pods. 

Link to post
Share on other sites

@ScutBoy thank you!  
 

This appears to be SMD mounting. I think it can be converted to through hole DIPs. But I may keep it the same way. DIP and PLCC processors are available. @Kai Robinson I was initially worried that these were some kind of custom logic chip but appear too small for that and do share the same package as the SRAM. What is your level of confidence that these are SRAM?   
 

The only contingency that would remain is simply the custom BBU. I found a company in China that can get the equations from the chip by various processes but it will exceed $600 (their minimum price - and it’s destructive). I’m hoping once the breakout comes in, I can assembly it and send it to @asicsolutions for review.  

Edited by maceffects
Link to post
Share on other sites

@maceffects For the BBU - i'd be willing to stump up a spare BBU - FOR THE CAUSE. As well as the $. I'm due to cash in some stock options again this year to put down a 20% house deposit - i can spare $1000 for this.

 

Regarding the plug in board - tbh, i'd map out the schematic of it - then i'll make a board design based on it - with SOIC parts, still, but with a SMD PLCC socket for the CPU. For SOIC - you can hand solder these parts, no need to use hot air. 

Link to post
Share on other sites
9 hours ago, Kai Robinson said:

@maceffects For the BBU - i'd be willing to stump up a spare BBU - FOR THE CAUSE. As well as the $. I'm due to cash in some stock options again this year to put down a 20% house deposit - i can spare $1000 for this.

 

Regarding the plug in board - tbh, i'd map out the schematic of it - then i'll make a board design based on it - with SOIC parts, still, but with a SMD PLCC socket for the CPU. For SOIC - you can hand solder these parts, no need to use hot air. 

 

I'm going to see what we can do without having to spend any cash now.  I am really hoping to be able to clone the Brainstorm BBU rather than the stock BBU as it will be something we can learn from and be able to possibly make better than stock BBU without people needing the 16mhz PDS upgrade part as well.  I'm really mainly concerned that I don't want to waste the BBU/PDS with destructive reverse engineering as I'd like to return it to ScutBoy in the same condition.  However, if i KNEW with a high level of certainty that China would be able to provide us the info needed to reverse engineering, it might not be an issue as I can simply make new parts for him.  Destructive reverse engineering is a last resort, however, if you want to do a stock one that would be helpful too.  I don't want to spend $600+ on making a stock BBU design.  But maybe either can give up their secrets and allow us to know what to do. 

Link to post
Share on other sites
On 12/31/2020 at 10:18 PM, maceffects said:

@Kai Robinson they look lovely.  Excuse my potential ignorance, but isn’t the SE limited to 1mb SIMMs?  And if I recall many Macs of this era didn’t like 3 chip memory SIMMs.  If you think we have a way to allow more memory, I’d be very keen on learning more. 


Actually on Paper the 68000 supports up to 16Mb of RAM... 
I suspect because of the limited amount of Bus Lines to/from the SIMM Slots is the Limiting Factor for the Base Model SE; that and that the ROM would need Modification to Recognize/Access Limits Higher than 4Mb...

IDK; but it is possible that there is a Physical Hardware Block or Value/Signal sent/set to the CPU; for instance the difference in cutting the resistor to allow for 1Mb SIMMs over 256k SIMMs...

I suspect that it might be possible to make some RAM chips that would Max out the RAM abilities of the CPU... Technically you can make Half Meg (512k) chips too... For Instance a 1.5Mb SIMM might be a fair starting place since you have a 3-Chip module setup; so if you put 3-512k RAM chips on it, it might not be too much additional memory range to utilize... 

I have a feeling that with a properly designed SIMM a 2Mb SIMM could be made/used; possibly even a 3Mb SIMM which since you have 3-chip modules slap on 3-1Meg chips and see what happens...

I believe that 12Mb is Obtainable...

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...

×
×
  • Create New...