Recent content by SuperSVGA

Here is a pinout if it's helpful:

It sounds like unstable power especially if it's inconsistent in how far it starts up. Are you able to check the +5V rail with a multimeter?

You would have to completely move them out of their current space from the code side in order to have contiguous RAM. This does unfortunately involve patching the ROM in many places to change the addresses for ROM, SCSI, sound, video output, and system error storage.

Depends on how much RAM you want to add. What you would want to do is change where the CPU thinks the memory locations are (i.e. edit the ROM to change their locations) but the logic board would need them accessed from the same location. For example how I would do it: RAM, ROM, a 68000, and...

Without separating the CPU from the computer in order to rewrite addresses, you would have to move other devices on the bus to different parts of memory. You could get up to 5.5MB just by moving the ROM, but now the SCSI address space in the way. If you moved SCSI, you would get up to 8MB where...

It doesn't take much, the basic process is disabling the built-in ROM with the switch/jumper on the board, putting the ROM on a PDS card, and making a few patches in ROM to make sure it finds it at that higher address. The PDS card has a CPLD to decode the right addresses, but you could do it...

The Disk ][ card did not have any PALs, it was all general logic and two PROMs. I fit it all into a single ATF1504 at one point, including the PROMs.

Unfortunately the 68000 only had 24-bits of address lines connected. To address additional memory you would need to implement some sort of bank switching/MMU. It wasn't until the 68012 which had 31-bits connected, or the 68020 which had 32-bits.

The Portable tops out at 9MB (not sure about the PB100) but I moved the ROM higher into the memory space to make space for 15MB of RAM.

One thing I was thinking about lately, who has the most powerful/fastest/most capable 68000 Mac out there? I’m only counting the original 68000 processor here, once you get into the 68020/68030/68040 you have a lot more performance related aspects to consider (MMU, bursting, larger address...

It's through the serial testing interface that's available in pretty much every single Macintosh with a serial port since the SE. The general method of accessing it is by connecting to the modem port with a serial terminal of some sort (for example a modern computer and a USB to serial adapter)...

Since it's returning 2 that means it's the second ROM (I think that would be MH, I can't remember) that failed checksum and the others all tested fine.

If switching to another known good ROM set doesn't work then it's probably an addressing issue. You're clearly getting far enough into the ROM for it to run tests, meaning all four ROMs are are working up to that point, but perhaps because of the address line issue the rest of the ROM space is...

The DIP-28 could definitely fit everything you need in roughly the same footprint. Here's a rapidly put together render: The PLCC-44 form factor would take a bit more but is still doable if you stack boards:

If you're not intending to connect a physical disk drive you could probably just leave the programmable logic out and just use the microcontroller alone. You could fit the entire IWM on a CPLD, but there's no point if having the microcontroller talk directly to the bus is an option.