Jump to content

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


Recommended Posts

  • 68kMLA Supporter
4 hours ago, cheesestraws said:

What errata are between this and the board you sent me (1.4something?)?  The short at the PDS card slot (where is best to cut that?) and the missing 26LS32 connection?

 

Missing A5 line (tie it to he ROM socket, and it's working again. 

Link to post
Share on other sites
  • Replies 939
  • Created
  • Last Reply

Top Posters In This Topic

I think there's a mistake in the Bomarc SE schematics.

Pin 2 & 4 of the SND chip are respectively linked to pin 4 & 2 of the VIA chip in the Bomarc schematics but I found out they aren't swapped and pin 2 of the SND chip goes to pin 2 of the VIA chip and same for pin 4.

 

Hope it is useful for those checking @Kai Robinson's board using the schematics. :) 

Link to post
Share on other sites
  • 68kMLA Supporter

Just a quick one - we can eliminate another annoying to find IC from the list - the MC3488 (Dual Line Driver) can be replaced with the SN75150, which makes sense since later machines use the SN75175 Quad Differential Driver. Pinout is identical, function is identical. Best thing is they're only £1.36 a piece from Mouser Electronics. 

I've busted out my IC tester to re-verify the 74F257's and 74LS245's - they check out fine. I've gone over the board again, and bodge wires are a thing, still, just double and triple checking that everything is connected where it should be.

Link to post
Share on other sites
  • 68kMLA Supporter

So uhh... This happened:

 

https://hackaday.com/2021/02/08/recreating-the-mac-se-logic-board/

 

I'm a little confused and a little irritated about it. The article has basic errors and I wasn't even consulted about it before it was posted. 

 

Bit rude, imo. 

 

Did anyone here submit it to them? 

Link to post
Share on other sites
  • 68kMLA Supporter

OK - back to what's going on - I'm reading the guide to macintosh hardware and i've come across this:

 

When power is first applied to the Macintosh SE computer, the following sequence of
events takes place:

1. The Sony sound IC monitors the voltage levels on the board and asserts the /RESET
signal until 0.25 second after the voltage has stabilized.

2. The /RESET signal causes the CPU, the BBU, and all of the internal devices to come to a
known initial state.

3. The Sony sound IC deasserts the /RESET signal and the CPU looks at the first four
words in memory (starting at location $00 0000) to get the Reset vector. When the
BBU is reset, it starts up with the ROM overlay address map, which puts ROM at
location $00 0000. In the ROM overlay address map, an address to a location in the
range $40 0000 through $43 FFFF is also decoded by the BBU as an address to ROM.

4. The CPU goes to the memory address pointed to by the Reset vector and begins to
execute the code it finds there (the Reset handler).

5. One of the first instructions in the Reset handler is a jump to a location in the range
normally assigned to ROM ($40 0000 through $43 E800). The first time the BBU
receives an address in this range, it switches to the normal address map. In this address
map, RAM is located at $00 0000 through $3F FFFF and ROM is located at $40 0000
through $43 FFFF.

6. The Reset handler carries out the startup procedure described in Inside Macintosh

 

I wonder if there's a voltage issue somewhere that means the SND isn't releasing the /RESET pin...

Link to post
Share on other sites
  • 68kMLA Supporter

More musings from cycling through that massive tome....for the floppy control logic in the GLU - it can be replicated with a single 74LS125 and a 74LS04...that'll sort the inverted WR signal and the ENBL1/ENBL2 signals. The spare inverter and buffer can be connected to make the SCSI IRQ's pass to the BBU...then it's 

Now just need to sort out the clock buffering - presumably a non-inverting buffer gate would suffice...? The Mac Plus feeds the oscillator signal into a single 74F04 (U4D) - question is, why inverted, rather than non-inverted...?

 

Screenshot 2021-02-12 at 4.42.55 pm.png

Screenshot 2021-02-12 at 5.03.28 pm.png

Edited by Kai Robinson
Link to post
Share on other sites
  • 68kMLA Supporter

OK. So....some KiCad and i've done a thing. Made a GLU replacement with discrete logic using tiny VQFN parts. Will get JLCPCB to do a batch of 5, with assembly. Should be fairly cheap - the VQFN's are about 50p each.

GLU Replacement.jpg

Link to post
Share on other sites

@Kai Robinson I'm pretty sure the only reason why the Mac Plus inverts the clock signal is because that must have appeared to be the most convenient chip-saving layout.

 

Good to know it is the Sony SND chips that's responsible for generating the power-on-RESET signal.  I believe the interesting thing about the RESET signal to the BBU is that it is not actually a chip-level RESET but rather primarily used to reset the overlay bit and a small amount of select other information.  The point here is that when you press and hold down the programmer's RESET button, the screen contents do turn to garbage, so the BBU itself must have its own internal power-on-RESET for the DRAM control and screen scanning state.

Link to post
Share on other sites
  • 68kMLA Supporter
14 hours ago, maceffects said:

For those not on this Facebook group. Here is the guy who designed the Mac SE logic board. 

60952514-4ECD-4B1A-80BF-3B1B7F010080.jpeg

 

Can you direct him to this thread so we can pick information from his brain? :D

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

 

Can you direct him to this thread so we can pick information from his brain? :D

Several of us did :)

 

I think he might be worried he's forgotten everything :( Hopefully he joins in anyway because any insights will likely be extremely helpful.

 

Or contacts!

Edited by Phipli
extra sentence
Link to post
Share on other sites
On 2/8/2021 at 9:32 PM, Kai Robinson said:

So uhh... This happened:

 

https://hackaday.com/2021/02/08/recreating-the-mac-se-logic-board/

 

I'm a little confused and a little irritated about it. The article has basic errors and I wasn't even consulted about it before it was posted. 

 

Bit rude, imo. 

 

Did anyone here submit it to them? 

 

This is astonishing - the nerve of some people! It seems that a user named toru173 sent them the link but the 68kmla account by that name was only made six days ago... Hackaday is a fairly washed-up outfit, I don't think they even have a real human vetting the articles they are sent. 

Link to post
Share on other sites
  • 68kMLA Supporter
4 hours ago, PowerMac_G4 said:

 

This is astonishing - the nerve of some people! It seems that a user named toru173 sent them the link but the 68kmla account by that name was only made six days ago... Hackaday is a fairly washed-up outfit, I don't think they even have a real human vetting the articles they are sent. 

 

toru173 reached out to me - please don't blame them for this - it's easy to get swept up in excitement/possibilities of the project. 

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

 

toru173 reached out to me - please don't blame them for this - it's easy to get swept up in excitement/possibilities of the project. 


Oh no, I didn't mean for any animosity. It sure would be sweet if this article ended up getting some more wind in the sails of this project. 

Link to post
Share on other sites
  • 68kMLA Supporter

Any idea how you are going about the I/O shield/frame/mounting tab metal piece?

Desoldering the old one is possible but it's not really an easy task (+ on most of my battery-disaster boards they are heavily rusted)

Did you try if the board holds in place without the mounting tabs holding it?

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...