Booting Mac Plus right from ROM + some games!

[unity]

So a small adapter board to sandwich in between would not work?

 

[MinerAl]

I looked at this a bit further, and there's a small difference between the Mac 128K/512K ROM socket and the Plus ROM socket (beyond the difference in space between chips on the motherboard). So even if you could cut the adapter board in half, it still wouldn't work in the 128K/512K. Fixing it should be pretty simple, but it means there can never be a universal adapter board that works in all those machines. There will need to be a version A for 128K/512K, and a version B for Plus.

How do you put (actual) Plus ROMs in a 512K to make it a 512Ke then?

 

[unity]

I was going to ask too, but I thought maybe I was reading it wrong.

 

[uniserver]

stock plus rom's to pop right into a 128 / 512k.

Bmow is talking about Robs's rom's, pretty sure.

 

[bigmessowires]

How do you put (actual) Plus ROMs in a 512K to make it a 512Ke then?

The spacing between the two ROM sockets is different for the Plus and the 128K/512K/512Ke. That's the main reason a single adapter board for all those machines would be problematic.

The sources of the ROM sockets' chip enable and output enable signals are also different between the two types of Mac. The difference doesn't matter when you're doing a normal 128K ROM swap to turn a 512K into a 512Ke, but it does matter when trying to build a sneaky adapter to give you 1 MB of ROM. 

 

[trag]

I'm looking at the photos and it really doesn't look like you need the board at all. Simply bending four pins up and soldering wires from point to point will do the exact same purpose so the 512K mod is still possible. You just need to be good with an iron.

Now mind you I can't look at the actual layout files and confirm this because he's using formats that Eagle can't make any sense of. Fffs.

He's using OsmondPCB for the layout.  He gives a link to the software which is a free download so you can view the files.  Osmond is the only Mac PCB layout software of which I am aware, and there are PPC and Classic versions available.

His hack using the .print driver was interesting, but I wonder if he is aware of the ROM hook that Charlie told us about some years ago.  Older fellow who dropped in for a few months or years a while back.  He did some cool work on animating gif presentations on early Macs, I think.  I can't remember his exact handle.  Maybe it was Charles with a 3 instead of an e?

 

[trag]

His hack using the .print driver was interesting, but I wonder if he is aware of the ROM hook that Charlie told us about some years ago.  Older fellow who dropped in for a few months or years a while back.

Henry, not Charlie.  His handle is/was H3NRY.   Here's a tidbit:

"Hi trag, yes you remember right, but why anybody'd want to add ROM code to a 25-year old Mac is beyond me. In the day, we needed to add code to init our SCSI port and support the Micah hard disk in the 64K ROM environment. The need for that went away with the Mac Plus ROMs which had SCSI and HD support built in, as well as support for more than 512K of RAM."

https://68kmla.org/forums/index.php?/topic/10261-video-playback-on-plusclassic/?p=109856

I think he discussed that hook in another posting somewhere.  It may be worth searching his posts.  There probably were not that many of them.

 

[uniserver]

Wonder if there is any way to pop some (Fancy Rom's) into a 128k or 512k and using some kind of modern technology, flash or something, that can somehow patch a way to get around the lack of ram, like flash virtual ram.  AH, i guess its just much easier to use a Mac with more ram.

 

[trag]

Ah, and here he discusses, very briefly, the memory address in question adn the boot behaviour:

https://68kmla.org/forums/index.php?/topic/10261-video-playback-on-plusclassic/?p=109960

Turns out H3NRY was very active while he was here, until 2012, it appears.   I think his wife had health problems that may have caused him to no longer have time for these boards.

There's some very interesting hack-worthy info in some of his postings.  It appears he was the VP of engineering at Nuvo Tech, IIRC.

 

[bigmessowires]

Cool. The same hook for "test software" appears several places in the Plus ROM (128K ROM) too. It's literally the very first thing the ROM does when booting. If the long value at $F80000 is $55AAAA55, then it jumps to the address pointed to by whatever's at $F80004. There are three or four other similar checks during the boot sequences, at other addresses in the $F800xx range. I wonder what you'd do with that. I wonder how you could even add extra ROM that would get activated by memory accesses to that address range.

I think this would be most useful for some kind of temporary clip-on testing device containing extra software to do validation testing at the factory. If you want to permanently change the Mac's ROM-based behaviors, you're probably better off just replacing the ROMs.

 

[trag]

Cool. The same hook for "test software" appears several places in the Plus ROM (128K ROM) too. It's literally the very first thing the ROM does when booting. If the long value at $F80000 is $55AAAA55, then it jumps to the address pointed to by whatever's at $F80004. There are three or four other similar checks during the boot sequences, at other addresses in the $F800xx range. I wonder what you'd do with that. I wonder how you could even add extra ROM that would get activated by memory accesses to that address range.

I think this would be most useful for some kind of temporary clip-on testing device containing extra software to do validation testing at the factory. If you want to permanently change the Mac's ROM-based behaviors, you're probably better off just replacing the ROMs.

I think you would do this with some additional hardware and/or replacement ROMs.   It's gives a built-in method to add functionality.  I agree that it probably makes the most sense that Apple had it in there for some kind of clip on test hardware or similar.    But as long as it's there, we can bend it's true purpose to our ends, yes?

In this particular instance, I was wondering if Rob could have used this hook for loading his code, instead of replacing the .print driver as he did. 

 

[bigmessowires]

I finally had a chance to build a Plus ROM adapter today and try it out. Unfortunately it was a lot tougher than I expected, and I couldn't get it to work. I didn't anticipate the trickiness of soldering four rows of headers on the bottom of the board and two DIP sockets on the top, while keeping everything perfectly aligned so it would fit in the motherboard's ROM sockets. Mine was a little off, and I couldn't get it to fit right. I also had trouble running clips to the address lines on the CPU. My RAM SIMMs are slightly taller than what I think is standard, and the last SIMM blocks enough of the CPU that it was impossible for me to get the clips to stay on when the SIMM was installed. Then to add insult to injury, I couldn't even fit the motherboard with ROM adapter back inside the chassis, because it collided with the cross-piece at the rear just above the motherboard slot. Arghh! I did finally bend and wiggle it in there, but when I hooked everything back up the machine wouldn't boot.  It's still an awesome idea, just not quite as "plug and play" as I'd hoped. I'll chill out and try again with another board later.

 

[uniserver]

lol

its just like anything easier said then done

 

[MacJunky]

I didn't anticipate the trickiness of soldering four rows of headers on the bottom of the board and two DIP sockets on the top, while keeping everything perfectly aligned so it would fit in the motherboard's ROM sockets. Mine was a little off, and I couldn't get it to fit right.

Tossing some spare sockets on the free ends of the headers to hold them straight during soldering should help.

 

[bigmessowires]

Yup, I did use spare sockets to make sure the headers for each ROM chip were aligned, but I don't think there's any way to stabilize the gap *between* the rows of headers for the lo and hi ROM sockets, since it appears to be a non-standard spacing. So while my headers for each ROM socket were exactly 0.6 inches apart, I think the gap between them may have been slightly off. I guess I could try soldering everything together while it's actually plugged into the logic board sockets, that would guarantee it should fit.

 

[trag]

 Then to add insult to injury, I couldn't even fit the motherboard with ROM adapter back inside the chassis, because it collided with the cross-piece at the rear just above the motherboard slot. Arghh!

Back in the day....

The upgrade companies that sold piggy-back upgrades for these machines recommended that you do this:

Turn the machine upside down.   Take the logic board and slide the left or the right side into the frame/chassis slot for that side.  Gently take a flat-head screwdriver and pry the other side of the frame/chassis outwards just enough so that you can slip the other edge of the logic board into its slot.   Voila; logic board installed while avoiding rear cross-bar.

 

[bigmessowires]

Rewritable ROM disk for Mac Plus: achievement unlocked. http://www.bigmessowires.com/2014/12/20/rewritable-rom-disk-for-mac-plus/

Bbraun put together a new version of the Plus ROM adapater board, with one extra chip on it for generating the correct output enable signal for the flash ROM. Then I dusted off my Metrowerks Codewarrior skills, and wrote a little Macintosh program to do the in-system flash update. It helps that I recently did almost exactly the same thing for my 68 Katy breadboard computer, which coincidentally used the exact same flash ROM chip, and a 68000-family CPU, so I knew it could be done.

The Mac program reads 128K of data at a time from the image file you select, then disables all interrupts, does the magic incantations to unlock the flash ROM, and writes the new data to flash. It takes about 60 seconds to update the entire 1 MB contents of flash memory.

View attachment 4997

 

[techknight]

now THAT... is cool.... 

 

[CC_333]

What can it be used for? Bootable ROM disk?

We have a bunch of Pluses we can install these things in. I think it would improve their value considerably [] ]'>

Anyone figured out something similar for the Mac SE/Classic/Classic II yet?

Save for any architectural differences, accomplishing this on the SE shouldn't be too difficult (given that the ROM chips are socketed in a similar fashion as the Plus).

c

 

[markyb86]

Off Topic: Do you have an easy solution for getting screenshots from the 68k's to the modern web? I was using photoshop 1.0 to convert them to gif, then FTP'ing them over.