Jump to content
Sign in to follow this  
johnklos

Rewritable ROM for the Mac Plus from Hackaday

Recommended Posts

It is really is an elegant solution to yanking them out and using an external programmer. If the ROM expansion ever happens for the Classic II, I hope your program can be updated to support it as well.

Edited by Paralel

Share this post


Link to post
Share on other sites

 

[steve] then dug in and created an old-school Mac app in Metrowerks Codewarrior to write new values to the ROM.

Wait, so you can program the ROM from the Mac?

Share this post


Link to post
Share on other sites

http://www.bigmessowires.com/2014/12/20/rewritable-rom-disk-for-mac-plus/

 

 

Stuffing new technology into old hardware is fun. How about a bootable, rewritable ROM disk for a Macintosh Plus, using modern flash memory? Dream no more, the reality is here. icon_smile.gif Using a small adapter board, the original ROM chips on the Mac’s logic board are replaced with 1 MB of flash ROM. The flash ROM contains a modified copy of the original Apple ROM data plus a special disk driver, and a disk image occupies the remainder of the 1 MB of flash. When powered on, the Mac can be booted from the built-in ROM disk with a single key press. When necessary, the contents of the ROM disk image can be rewritten from within the running system, using a custom-made flash updater program. You can fill the ROM disk with system software and a couple of games, or whatever you want to show off without needing a disk. The same thing should be possible for the Mac 128K and Mac 512K too.

 

Share this post


Link to post
Share on other sites

128k part sounds interesting.   I really want to push the 128k and just first hand see all of what i can run on it.

maybe do some more HD20 testing with it as well.

Share this post


Link to post
Share on other sites

haha YES:-)  maybe they will allow my comment?

 

 

 

  1. Charles says:

    Your comment is awaiting moderation.

    Vintage Mac is awesome. Thanks to everyone that helps support our community!
    Mike from Australia and his SCSI2SD, Steve with his Floppy Emu/ HD20 Emu, Plus Rom Hacks, IIx,IIfx,IIcx,IIci,IIsi,SE/30 (2mb and 8mb) Programable Rom Simm hacks from Dougg3 and S/W by bbraun. jt for all his mac hack knowledge (IIsi radius pivot video card in the SE/30) Techknight with a 7/8mb ram expansion card for the Mac Portable, Max for his hand made active terminated SCA to SCSI adapters. gnolivos for his 3D printed floppy gear replacements for the auto-eject assm. And many others from Over Clocking to new Pram Battery adaptor boards.

Share this post


Link to post
Share on other sites

Yeah, these will give that big pile of mostly worthless Pluses we have a very excellent boost in their value, I think (they will make the 512k more versatile as well, given their lack of on-board SCSI). They probably won't sell for as much as an SE/30, but with these they will probably go for at least enough to break even.

 

c

Edited by CC_333

Share this post


Link to post
Share on other sites

I differ on the value of the pluses, the HD20 emu basically solved the problem of Pluses having serious limitations. Now its essentially no different than a Macintosh Classic, it just lacks the internal SCSI, but does take regular SIMMs compared to the Classic and its weird RAM card.

Edited by Paralel

Share this post


Link to post
Share on other sites

Good point!

 

But it does help the Plus's value that the ROM can now be messed around with in creative ways, giving it functionality it never had before (like booting from a ROM disk, for example).

 

That has been done on the SE/30 and most of the Mac II family by way of dougg3's custom ROM SIMM, and it's been absolutely invaluable in terms of all the extra funcionality it can add (which makes those models more desireable).

 

c

Share this post


Link to post
Share on other sites

This is what I'm hoping for with the planned ROM card for the Classic II. It should be possible to put an entire barebones System 7.1.x install in the ROM space.

Edited by Paralel

Share this post


Link to post
Share on other sites

Yeah, and then all compacts (except the Classic, for now) will have a customizable ROM with space for a boot disk image. How exciting!

 

And just think, all this was considered a pipe dream when these machines were current (or, indeed, right up until just a few years ago).

 

I wonder what will be next? Custom ROMs for PPC Macs up to the beige G3?

 

c

Share this post


Link to post
Share on other sites

...I remember seeing a webpage years ago explaining how to locate the ROM disk in a Classic ROM dump, extract it to a disk image, modify it, then put it back again, giving you a rom dump with a custom disk image (it wasn't too large though, only a few hundred KB IIRC, enough for System 6 and a couple of apps).

 

I wish I could find this info again.

 

It'd be a quick way to giving a Classic a custom ROM disk (should you be able to replace the ROM chips with rewritable ones).

Share this post


Link to post
Share on other sites

well there is 2 versions of Classic II main boards.

 

 

there is the 4 chip version…

ClassicII.jpg

 

 

 

 

 

and i am pretty confident that with (this)… i can do what parallel is talking about.  with the dougg3 programmer, and with this new simm he has made!

 

DIPSIMM.jpg

 

 

 

 

and this is not just (rev 1) Classic II excitement… this is LC-I and LC-II as well!!!   /performa variants

 

The only issue is the later version of classic II has different roms,  only 2,  longer ones.

classicII-rev2.JPG

 

so look to see what board you have.

Share this post


Link to post
Share on other sites

Mine is the 4 chip version, as in your pic. I guess the only thing you'd need to do at that point is put the ROM's on a card with the pin-out that matches the weird interface it has. It should also be possible to combo an FPU on the card as well, if I remember correctly, then you'd really have a sweet product on your hands. FPU + ROM expansion.

 

One would probably want to re-write the ROMs on the logic board as well to reclaim the 1/2 megabyte that is just sitting there blank, that would give one 3 1/2 megabytes of contiguous ROM to play with, since all 4 megs gets put into a contiguous memory space despite being split between the motherboard and the card. That's quite a hunk of space. I have no doubt I could get System 7.1.2 down to 3 1/2 megs easily.

Edited by Paralel

Share this post


Link to post
Share on other sites

Or find out if the RAM card interface has enough of the databus to contain a ROM/RAM card. Then you can run the appropriate jumper wires. IT would be universal at that point. 

 

The Classic II, the RAM slot is actually a ROM expansion slot. So it would just be direct plug/play. The Classic 1, youll probably need a couple jumper wires. 

Edited by techknight

Share this post


Link to post
Share on other sites

It actually isn't a RAM slot on the Classic II, it was always meant for an FPU/ROM card, that's why there are spots for RAM SIMMs on the main board. Although it looks similar to the RAM card interface of the Classic I it was never meant to serve the same purpose as a RAM expansion point.

Edited by Paralel

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

×