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Booting Mac Plus right from ROM + some games!


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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.

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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.
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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. :)

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 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.

Edited by trag
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  • 2 weeks later...

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.

 

post-1779-0-13221300-1419118331_thumb.png

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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

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lol can’t you tap into the 3 megs between SCSI and SCC ?  icon_razz.gif

sorry you give me and inch and i am trying to take a mile icon_smile.gif Flashing on on the fly… ( in machine ) is super awesome… Wonder if your software could be used with Dougg3′s 2mb and 8mb simms ? lol then people will not need to buy his programmer.

 

not that dougg3's programmer isn't awesome...   

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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. 

 

I actually ran the program under Mini vMac in Windows to generate the screenshot. :)

 

Yeah, you still need an external EPROM programmer to do the initial programming of the flash chips - you can't just stick blank ROMs in the computer and boot it up. But once the ROM has been programmed once, you can use this Flash Tool to update its contents without removing the chips from your Mac. If you could get a friend to do the initial programming for you, or buy pre-programmed chips, then in theory you wouldn't need an external EPROM programmer at all. But techknight's right about the risk of some unexpected error writing bad data to the code section of the ROM, essentially bricking the Mac until you reprogrammed the flash chips externally.

 

I looked into it a little, and I don't think it's possible to extend the ROM area beyond 1 MB without multiple hardware and software changes. In theory it's probably doable, but not really worth the effort. 1 MB is a good number. :) But maybe someday...

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bbraun used wires with test clips, check out his photo:

 

plusrom-small.jpg

 

I was never able to get that to work, though. There's very little clearance between the CPU and the SIMMs, and between the CPU and the chassis frame. A couple of times I was able to get clips to stay put long enough to try sliding the logic board back inside the case, but the wires always caught on the chassis and ripped out.

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LOL! Powering up my good IIsi to to test a 12" RGB with a pair of those same clips hooked up to address lines on MDU killed it deader-n-a-doornail! I forgot I had a few PDS Cards stored inside on top of them . . .

 

OOPSIE!!!!!!!!!!!!!!!!! ;D

 

I'm still lovin' those clips though. On power-up that IIsi board now does the most amazing VampireVideo ScreenDump! :D

Edited by Trash80toHP_Mini
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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.

I have had good luck with a similar approach -- copy the files to my netatalk server and use GraphicConverter on my Mac mini with Mac OS X 10.9 or 10.10 to convert them to PNG files. It works really well, at least with the screenshots system 7 saves.

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OK, the universal ROM adapter for Mac Plus, 512Ke, 512K, and 128K is working! It's a single PCB with two sets of socket footprints, so depending on where you add the sockets it can fit logic boards with different chip spacings. I built two of them, one for the Mac Plus and one for the Mac 512K, and they both work. 128K is untested, since I don't have one, but it should work.

 

bbraun's ROM disk driver initially had some trouble on the 512K, but I managed to fix that, so now it's smooth sailing.

 

I also made some improvements to my Flash Tool used for in-system ROM updating, so now it's a little more idiot-proof. Just choose which area of ROM you want to update, select a data file to use, and the tool does the rest. It also validates that the file is the right size for the area of ROM you said you wanted to update, to help reduce the chances of bricking your Mac with a bad update.

 

flash-tool-1.5.png

 

Flash Tool currently won't run on a Mac 128K, so while you can use the ROM adapter board on that machine, you can't do in-system updating of the ROM contents on it. That may be solvable… not sure yet.

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Funny you mentioned it. I looked at that, and it's certainly doable, but more complex than I thought. The same Macintosh icon data is shared for sad mac, happy mac, and possibly some others. Then the "face" data that appears on the mac screen is stored separately. So without a pretty big code change, you could turn the happy mac icon into a bug-eyed mac or something, but you couldn't change it into something completely different.

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