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Great to see you back around here @bigmessowires.  It would be a good idea to pick a particular permissive license or public domain dedication for the parts of Plus Two that you authored.  I personally would have more openly shared info about the project if the license was more clearly stated.

Welcome @Hiro256! Psst!  Fine, I digress, if you're looking for a single FPGA design, Steve Chamberlin had done that 9 years ago and dubbed it the Plus Two.  To my knowledge no one has ever been interested in picking that project up to polish it off, probably because the license/copyright...

What I've been thinking to myself about my knowledge of Verilog... I needed a few more classes to fill up my computer science degree electives and the relevant classes seemed like something that wasn't too over-hyped or overly specialized.  Probably not going to use it at my main job any time...

Hello @SlickClick, welcome!  In this case the master clock should be ~16MHz and the BBU divides that down to the ~8MHz CPU clock.  Have you actually run a Macintosh SE with a higher speed master clock?  I would have suspected that higher master clock speeds wouldn't work at all without a BBU...

@Kai Robinson Yeah I believe I looked at that one.  The other thing I was thinking was that a CPLD might also fit the bill, the advantage being voltage level shifters would not be required.

@Kai Robinson Possibly... one thing that makes me think about is setting up some sort of independent "hardware test fixture" like I've designed (but haven't yet tested) for the RTC chip, but for the BBU I'm still tweaking the logic and setting up the simulation test.  Things have been exciting...

@PotShotScott I'd agree... part of the idea of making the replica boxing, complete with shaped foam blocks, is that it provides additional assurance to the customer that the vintage Macintosh is being shipped in pristine packaging and it is therefore less likely to get damaged in shipping. ...

So looks like the state-of-the-art in open-source FPGAs is still pretty much "Lattice only."  Fortunately, looks like Lattice FPGAs might be good enough for implementing a replica BBU for the Macintosh SE.  Good thing was that I was already looking at candidate FPGAs from Lattice.

Losing legs from a ROM, ouch.  The price of those DIP64 IC test clips just keeps going up and up, but they're at least out there... https://www.digikey.com/en/products/detail/3m/923739-64/12091 Another note, I also looked deeper into the Unitron's logic equations and tried coding them up in...

Easy way to check the CPU is still working in some vein: If you can trigger *HALT + *RESET and it will respond by de-asserting/asserting *AS after a few clock cycles, it should be okay.

Oops, well... actually I'd vouch the essential chips are still working: GLU and BBU for one.  You can double check that the ROM and CPU are okay, and if so, that should actually be good enough for initial oscilloscope debugging.

Nice @Kai Robinson.  I've been taking a deeper reading of Guide to the Macintosh family hardware and it has been quite helpful in answering several questions on the specifics of the BBU, it also mentioned the double-pace video memory fetch.  The timing for the DRAM controller to respond to CPU...

Actually @Kai Robinson that last link was a new one to me, and it answers the question I had about the 3.7MHz clock!  Considering the Macintosh Plus does not generate a constant-period 3.686 MHz clock signal, but interleaves 3.133MHz and 3.916MHz periods, it is likely safe to assume the BBU does...

Nice!  Glad you were able to solve the problem by cleaning and tightening up the BBU socket connection.  I've been looking into re-implementing its functions and made notes about it on the reverse engineering thread that cheesestraws mentioned.  The BBU itself isn't a complicated chip, it just...

Missing address line A5, definitely can't boot without that.  :) So, I dove into seeing how much of the essential functionality of the BBU I could write in Verilog, and I have to say I'm surprised with the progress I've made so far.  As I've suspected, most of its features and functions can...

Hello folks who have voted on the previous poll about what kind of boxing you would want, I could really use some of your feedback on this question about the desired price point.  This will determine which remaining design efforts (if any) will be pursued before creating a crowdfunding or group...

@Kai Robinson The NXP chip definitely has a different software interface than Apple's custom silicon.  I'd say the chips definitely look handy for use in other projects (like a Raspberry Pi RTC), but ROM patches would be required to use it for Macintosh computers. One good note, looks like the...

That's the UL registration number, apparently the same registration number can be used by a number of different products?  Your battery also uses the "ER" chemistry code so it's also Lithium Thionyl Chloride chemistry.  Interestingly, my copy does not have a UL registration number on it.

Yes, when powered on, the RTC circuit is actually fed with 5V power, 3.6V will work perfectly fine. Also, nice that you've found the Lithium Manganese Dioxide cells!  Now I've looked at the photos in detail of the original VARTA battery I removed, indeed I see the original just says "3V".  If...

If the batteries are really as defective as we may believe, they would have self-discharged to 10% or less of original capacity in 35 years.