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I think the ROM overlay is usually 0x000000-0x1FFFFF, so I'm not sure why it would ever end up at that range. That part of RAM should only be a repeated image of the RAM, especially since video and sound memory is at the end of the RAM space. The stock Mac Plus ROM checks if the ROM is mirrored...

Did you ever nail down a pinout of the Outbound side connector? Also I'm curious if you've determined if the card is doing any address decoding to prevent Outbound memory space access from reaching the SE.

It looks like it brings pin 15 high/disabled for writes to 0x200000-0x300000. I don't know why off the top of my head though.

Following the pinout in your simulation image, the system RAM is actually MCAS2F and MCAS3F, and the minimal RAM on the MacSnap is MCAS0F and MCAS1F. You also seem to have pin 2 of RP6 shown as connected to ground rather than a pull-up for pin 1 on the 74LS253. I believe that pin is low when...

The upper 4 rows (B,C,D,E) are connected to data bits 0-7, while the lower 4 rows (F,G,H,J) are connected to data bits 8-15.

The general things you would need are: An adapter from the 34-pin Portable SCSI connector (male pins since the cable is fixed to the drive) to whatever SCSI connection you have for reading the drive (50-pin IDC, DB-25, 50-pin centronics, etc.) as well as some way to connect +12V and +5V to the...

There are a lot of ways you can do it, the signals are standard SCSI with a custom connector. I've done a bunch of drive imaging of Portable drives and typically use a custom ZuluSCSI RP2040 and adapter I built to image the drive with initiator mode, though there are several other ways you can...

Well the issue is likely the RP2040 and the design of the boards. On a normal SCSI device, when power is applied the terminators receive power and the SCSI bus is pulled up. No signaling comes from the SCSI device because SCSI device isn't ready yet. On the RP2040 it powers up with all pins in...

It would probably need some more testing, for example checking to see if the "powered on" +5V from Q11 is coming on, though I doubt it is. A few things I can think of right now: Check the reset and programmer buttons, make sure the signal is high and goes low when pressed Look at pin 9 of...

Well you're getting a good +5V which means a few things are likely working fine: The OpAmp for regulating the +5V The 1.2V reference used in regulation The comparator managing the "low battery" cutoff (you would not have +5V otherwise) The only other things on the hybrid from memory are: -5V...

Only the battery is necessary, assuming it is above the minimum voltage of around 5.6V.

I would start by checking the fuse, I have seen them blow just with a power adapter connected, or even a "turned off" bench supply connected to the DC jack, but not really sure why. Next if the fuse is good, take a look at voltages on Q16 with battery power connected to see if the main 5V is...

You would only need a pull-up on the power switch line, nothing on the 5V.

The biggest issue will be that you will need to patch a good bit of the Performer's control panel, as it applies ROM patches and also expects the memory map of the Plus/SE/Classic.

You wouldn't need any sort of advanced memory controller, a simple CPLD would suffice. With the processor, RAM, and ROM on the card, the only time you need to access PDS is to access I/O, display, etc.

I wonder if it would just be better to put the RAM and ROM on the accelerator card, and ignore the original processor entirely, that way the RAM isn't limited and you don't have to worry about the processor switchover.

It should just be a 68uH inductor, something like a Sumida RCH875NP-680K or Wurth 744731680 should fit good.

I'm surprised no one has cloned that CAS PAL chip yet, it's simple and much easier than most of the other reverse engineering efforts I've seen people do.

One of them looks like the Video Explorer:

I think something like the ST L7805ABV may work. Not all 7805s are quite the same and I don't remember what qualities are typically required, but the L7805ABV at least shows an example of it being used for negative voltage: I think the numbering may be incorrect on the schematic symbol, but...