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#1 2014-11-04 05:26:49

bbraun
Member
Registered: 2014-05-29
Posts: 1,064
Website

Plus ROM Hack

I mentioned this in my thread about compacts for trade, but I think some folks might have missed it.

Hopefully, we all know about dougg3's ROM SIMM, which allows a programmable ROM in IIx, IIci, IIcx, IIsi, and more systems, if they have a ROM SIMM slot.
I've done something similar, but for the Mac Plus (and probably the earlier compacts as well, but untested).  The address layout in these machines have 1MB of addressable space for the system ROM, although the ROM its self is only 128k.  Interestingly, the 28 pin sockets used by the ROMs have an additional address line going to them, bringing the total possible size to 256k.  By stringing 2 additional address lines from the ROMs to the processor, we can get a full 1MB of addressable space.
Two 29F040 flash ROMs can store 1MB, so all that's needed is an adapter:
adapters.jpg
plusrom-small.jpg

Having a programmable ROM with that much space is great and all, but what are you going to put in that 1MB?
I've modified the bootable ROM disk I made for dougg3's ROM SIMM, to work on the Mac Plus, and use an 800k+ ROM disk image in the remaining space.  That's not a huge amount of space, but for a Plus and System 6, you can fit a bootable system and some utilities or games on there.

I've made up a couple extra of these in case anyone else is interested.  I'd much prefer to use them to as a way to unload some of my Plus' (if anyone needs one, let me know!), but I'm willing to part with them separately too.

I've written up a little User's Guide on how to install and use it.

There's some more information at the following locations:
http://synack.net/~bbraun/plusrom/
https://mac68k.info/forums/thread.jspa?threadID=312&tstart=0

I've made up 5 extras right now, although I'm waiting on the 29F040 flash ROMs, and the clips to connect the address lines to the processor without soldering.

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#2 2014-11-04 05:50:34

uniserver
Member
From: Sf, Mi
Registered: 2014-05-15
Posts: 956
Website

Re: Plus ROM Hack

I just think this is great.
I guess if one uses an os that is much smaller then 6.0.8, then that leaves more room for App's smile


#I Re-Cap √Mac √NeTX √Amiga Boards - A/B - PSU# (MacCaps.com)  Modern SCSI HD's - For Old Macs - Pre Cfg'd - 10k RPM! 73gb!! $50 + free shipping  -- Mac 128K Re-Ram kits (16 Chips) $35 + shipping, Floppy Issues?-> Bourns Filter Solution 128k - SE/30, $16 + shipping

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#3 2014-11-04 05:51:58

uniserver
Member
From: Sf, Mi
Registered: 2014-05-15
Posts: 956
Website

Re: Plus ROM Hack

I would even think, maybe this would work with the Macintosh SE?   or might be another ball of wax...


#I Re-Cap √Mac √NeTX √Amiga Boards - A/B - PSU# (MacCaps.com)  Modern SCSI HD's - For Old Macs - Pre Cfg'd - 10k RPM! 73gb!! $50 + free shipping  -- Mac 128K Re-Ram kits (16 Chips) $35 + shipping, Floppy Issues?-> Bourns Filter Solution 128k - SE/30, $16 + shipping

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#4 2014-11-04 17:23:14

MinerAl
Member
From: The not-so-great plains
Registered: 2014-08-26
Posts: 73

Re: Plus ROM Hack

So Cool!

A System 3.2 bootable ROM (assuming it's much smaller than 6.0.x) with MacWrite and MacPaint and maybe a game or two would make these Plusses pretty sweet little appliance computers.  You'd need a serial printer though smile

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#5 2014-11-04 17:34:56

bbraun
Member
Registered: 2014-05-29
Posts: 1,064
Website

Re: Plus ROM Hack

Thanks!
Looking at Guide to the Macintosh Family Hardware, it looks like it should physically work for the SE, but the SE of course has a newer and larger ROM, so the current ROM image won't work, and the disk image would be <800k.

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#6 2015-01-02 18:34:16

uniserver
Member
From: Sf, Mi
Registered: 2014-05-15
Posts: 956
Website

Re: Plus ROM Hack

HAHA,  ok i just got the latest ( in machine re-writeable ) Plus ROM from bbraun...  Had to attach 3 wires to the CPU instead of 2 wires.

so A18 - A19 - R/W, its no big deal.

And i used BMOW's new Flash tool 1.2

bbraun helped me out and patched up my rom/rom disk for me,  he added BMOW's new HARP Mac Start Up bong patch too.

I hit the Go button on the software, screen went blank, and the first 3 sets of 128k writes to the ROM it was the normal bong,  Then The bongs changed into a HARP!!! haha
it was great.  ( maybe i am easily amused )
Then the last 3-4 sets of 128k writes were all HARP.    That is how his software works, Instead of seeing status, you hear Bongs per 128k writes.
Rebooted and it was all set.( all though rebooting was not needed )(just want to check to see if it came back up ok)  About the only thing i can say is, there is still quite a delay when your first power the plus on, with 4megs of ram installed.

Last edited by uniserver (2015-01-02 18:47:47)


#I Re-Cap √Mac √NeTX √Amiga Boards - A/B - PSU# (MacCaps.com)  Modern SCSI HD's - For Old Macs - Pre Cfg'd - 10k RPM! 73gb!! $50 + free shipping  -- Mac 128K Re-Ram kits (16 Chips) $35 + shipping, Floppy Issues?-> Bourns Filter Solution 128k - SE/30, $16 + shipping

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#7 2015-01-02 18:38:40

uniserver
Member
From: Sf, Mi
Registered: 2014-05-15
Posts: 956
Website

Re: Plus ROM Hack

also, physically, this plus ROM KIT almost fits in the SE, but there is still a slight bit of spacing issue, the rom sockets are a hair too close.
basically it doesn't fit though, you could make it, but its not going to work.

so looks like we would need 3 physical ROM adaptors.      128k - 512k / PLUS / SE

Last edited by uniserver (2015-01-02 18:39:01)


#I Re-Cap √Mac √NeTX √Amiga Boards - A/B - PSU# (MacCaps.com)  Modern SCSI HD's - For Old Macs - Pre Cfg'd - 10k RPM! 73gb!! $50 + free shipping  -- Mac 128K Re-Ram kits (16 Chips) $35 + shipping, Floppy Issues?-> Bourns Filter Solution 128k - SE/30, $16 + shipping

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