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quorten

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  1. @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. Also, it is perfectly fine if the replica boxing itself takes a few "sacrificial hits" in shipping while preserving the Macintosh inside.
  2. 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.
  3. 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 Verilog mainly to run a simulation that I could compare the BBU's waveforms with. Indeed this was helpful in answering a few last questions, though it did feel a bit like a "distraction" from the BBU. One interesting note, though, I found the Unitron's C3.7M clock is generated by i
  4. 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.
  5. 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.
  6. 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 memory requests looks rather tight, but it's doable if you use both edges of the 16MHz clock and slew rate limiting on combinatorial logic outputs. (Of we could simply use an internal 32MHz PLL and registered state transfers.) Regarding GLU, indeed a second look at the GLU equations I see no
  7. 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 likewise, rather than using a PLL and precise frequency division to get a more accurate 3.686MHz clock. The first link I saw earlier. Yeah, Pete Foley has his screenshot of the signals simulator source code, purportedly he's got the full thing hiding out. Hardware design tech has definite
  8. 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 has a lot of I/O pins and runs a 5 volts, which is what makes getting a drop-in replacement FPGA tricky. So yeah, always good if you can keep using the original BBU chips.
  9. 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 be implemented with just a whole lot of combinatorial logic, and the sequential logic is almost exclusively simple timers and counters of a sort. I feel that the integrated asynchronous DRAM controller is by far the most complicated part of the BBU, to show how simple the chip is... Here's a sne
  10. 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 buy campaign for the product. I'd like maybe 10 responses to get a good idea.
  11. @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 Acorn schematic is wired up expecting the same load capacitance from the crystal, but the Apple way of using a 10pF and 33pF capacitor together is probably cheaper than using a single 12pF capacitor due to specialized component costs.
  12. 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.
  13. 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 indeed the original was also Lithium Manganese Dioxide chemistry, that's pretty nice! My particular copy dropped down to 0.98V in 2019, though, so this is definitely a "your mileage may vary" thing. Lithium Thionyl Chloride batteries are at 3.6V, those are the ones that are used because they
  14. 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.
  15. Well if those Maxells aren't already exploded from sitting in inventory they must have something good about them! I have to admit, it's tempting to see leaded solder-in batteries being sold... yeah you could just solder in another battery for a more authentic looking board, but it's totally punitive to not use a battery holder or connector of some sort.
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