Creating a Mac 128Ke

[napabar]

I'd like to my hands on a Mac 128Ke for some experimenting. I actually had one of these back in the 90's when I owned a few 128k's. I remember being disappointed that it wasn't a "pure" 128K! Needless to say, I don't have it anymore, and they are almost impossible to stumble upon.

Which leads me to my question about creating one. Apple sold a kit for the Mac 128K and stock Mac 512K that included the 128K ROM and 800K floppy drive. They also had a kit for fully converting them to a Mac Plus, but the lesser upgrade did exist.

Shouldn't it be as simple as procuring a working Mac 128K and a Mac Plus, then swapping the ROM and Floppy drive from the Plus to the Mac 128K?

Is this particularly hard to do?

 

[Dennis Nedry]

It may be even cheaper and more readily available to buy two blank ROM chips and burn them with the Plus ROM. Here's what to do:

-Buy two ROM chips on eBay (someone here can recommend a part number).

-Buy a cheap Willem ROM burner on eBay.

-Hook the ROM burner to a PC's parallel port & USB port.

-Insert LO ROM, burn with LO ROM image. Repeat with HI ROM. (This may require splitting a Mac Plus ROM file if it's just one file, we can help you with this.)

-Put these chips into your Mac 128k and safely store the originals.

It is LITERALLY that easy to make your own ROM chips. If you have destroyed a Mac with this ROM (Mac Plus, 128ke, 512ke), or if someone who has can vouch for you, maybe this could be considered a legal backup copy if you're overly concerned about that sort of thing.

800k drives can also be had from eBay.

 

[Mac128]

Actually Dennis, it's probably a lot easier and cheaper to buy a Mac Plus off eBay. They are plentiful and cheap. It will also give one a place to safely store those removed parts from the 128K. Besides, I always recommend anyone with a 128K to also own a Plus since it is so similar to the 128K and has a SCSI port for use with Zip drives and such for transferring files back and forth between OS X and other Macs, and very helpful for troubleshooting and creating 400K disks. Easy to swap out and return the parts as needed.

 

[Dennis Nedry]

That does make good sense to have a Plus around. However, to use the Plus in that way, you must keep swapping the ROMs back into it which is a little dangerous. I always manage to bend the pins at least a tiny bit each time. Considering shipping, it may cost about the same, maybe just a bit less, to buy the burner ($30 shipped) and 2 ROMs ($10 shipped maybe?). So we're talking $40 and you get to keep the nice burner for other crazy projects.

The best solution is to do both I guess, so you have a handy Plus with its 800k and SCSI port and your 128ke. You could even dump the real Plus ROMs and burn exact copies without all the splitting business.

It is also possible to send blank chips to one of us and have us do the burning for you.

 

[napabar]

I'm not worried about reusing the Mac Plus. Just curious as to how easy/difficult it is to do the ROM swap.

 

[Dennis Nedry]

All that you need to swap ROMs is a flat edge screwdriver. They pry right out. You must pry just a little at a time from each side, back and forth, so that you don't bend the pins.

You also will need a very long Torx T-15 screwdriver to open the Macs.

Maybe the Plus will work normally with the Mac 128k ROMs and the HD-20 init?

 

[napabar]

All that you need to swap ROMs is a flat edge screwdriver. They pry right out. You must pry just a little at a time from each side, back and forth, so that you don't bend the pins.
You also will need a very long Torx T-15 screwdriver to open the Macs.

Maybe the Plus will work normally with the Mac 128k ROMs and the HD-20 init?

Thanks. Was wondering about what tools I'd need to pop the ROM out.

Don't think a Plus would work with the 64K ROM. Too many of it's new features depend on the 128K ROM, like SCSI.

 

[Gorgonops]

Thanks. Was wondering about what tools I'd need to pop the ROM out.
Don't think a Plus would work with the 64K ROM. Too many of it's new features depend on the 128K ROM, like SCSI.

It might be interesting to see how much of the Plus works with the old ROM. Obvious SCSI won't work, but... other than that addition the machines might be similar enough for the Plus to make it to the desktop if you boot it with an appropriate single-sided System disk. (It in particular might be interesting to see if the 64k ROM freaks out when presented with 4MB of RAM.) ;^)

Heh. If you're really bored you could rewrite this SCSI driver software to support the Plus's built-in SCSI, assuming the Plus boots with the 64K ROMs. The hardware is actually *very* similar. (It's one of the reason the Mac Plus' SCSI is so slow, even compared to the otherwise similar SE.) If you did that you'd make someone on this board SUPER HAPPY since then he could add a Dove SCSI board (which matches the Plus' memory map) to a 128k and have mass storage while preserving the sacred 64K ROMs for all eternity.

 

[Mac128]

The Plus boots fine with 64K ROMs. It's been done by both myself and Tom Lee. Neither of us used it extensively, but if I'm not mistaken, the 64K ROM was coded to be aware of at least 4MB of RAM if not more, up to the limits of the 68000. If not it definitely supports 512K RAM, which is the base configuration of the Plus. But even in the presence of 4MB installed, wouldn't the ROM simply ignore the higher RAM addresses?

Not sure I understand the Dove Mac Snap SCSI card comment, as it requires 128K ROMs and relies on the encoded SCSI instructions to function. If it were that easy there would not be so many threads devoted to it.

Dennis, your point is well taken, however, I was referrig to the whole package of the Plus, including the 800K disk drive which will probably cost more than the Plus by itself as well as additional shipping. I'm not sure the Plus ROMs by themselves would be so easy to come by either. At least with a functioning Plus, it offers many options aside from cannibalizing the ROMs whereas the equipment you recommend has a one time use for this purpose, as wells the learning curve to use it. For instance, it could be run more or less as a functioning 512K Mac. It could also make for a good parts donor when things start to fail on the original 128K, like the analogue board in particular.

IMHO, the whole Plus is the better deal, unless one wants to get into the business of burning and backing up ROMs, and other related experimentation.

 

[Gorgonops]

Not sure I understand the Dove Mac Snap SCSI card comment, as it requires 128K ROMs and relies on the encoded SCSI instructions to function. If it were that easy there would not be so many threads devoted to it.

The comment was in reference to the fact that if you compare the hardware design John Bass used when building his pre-Plus add-on SCSI board for Macintosh 128k/512ks it's *very* similar to the SCSI hardware of the Plus. (It's 95% accurate to say that only the memory locations differ, and in that only slightly.) For a capable programmer with access to the same developer tools John Bass used it appears it would be very trivial to rewrite his disk driver to work with the Plus' SCSI hardware. And since the Dove SCSI boards were compatible with the Plus hardware by extension a driver written on a 64K ROM-ed Plus would work on a real 128/512k equipped with said board and its original ROMs.

The reason's no one's done it is the *right* way to add a mass storage device to a Macintosh is to upgrade to the 128K ROMs. Apple made them available to everyone essentially for free with along with the very worthwhile double-sided drive upgrade. It's a completely pointless exercise to make SCSI work with 64K ROMs. That doesn't stop some people from wanting it.

 

[trag]

The much easier (although somewhat less reliable) method of getting Plus ROMs would be to find someone on the list with a chip programmer and the time to make copies into pin-compatible EEPROM or Flash chips. The Plus ROM dump from CopyROM will work as source, as long as one's programmer's software has the ability to interleave programming content across multiple chips, one at a time. IOW, program every other byte to this chip. Program every other byte starting with the second byte to this chip.

Only less reliable because one must depend on someone else to program the chips.

I don't have the time right now or I'd volunteer. I hope to eventually do something similar for IIfx and IIsi ROMs for the SE/30.

Ouch. Digikey's price on the proper EEPROM is $17 each and $8 - $11 for the Flash. Yow. At those prices, it's almost cheaper to build a circuit board to adapt a PLCC (little 7 x 9 x 7 x 9 SM chip) version to DIP.

 

[H3NRY]

If memory serves, a standard ROM chip doesn't just drop into the Mac 128, one pin needs to be jumpered for it to work. Easier and more certain to work if you have the genuine Apple chips. I think pin 1 of a 27C512 EPROM has to be lifted from the Mac's socket and a jumper wire run to pin 28 (directly opposite) because PROMs like Apple used have an active low chip enable and EPROMs are active high. Or something like that. I definitely remember putting jumpers on all the Beck-Tech ROM upgrades.

 

[Mac128]

The reason's no one's done it is the *right* way to add a mass storage device to a Macintosh is to upgrade to the 128K ROMs ... t's a completely pointless exercise to make SCSI work with 64K ROMs. That doesn't stop some people from wanting it.

I now understand your reference, the comparison the Bass' original design has been discussed numerous times in other threads. The trick of course as you so astutely point out is writing a driver for it, which few on this forum are interested in, or capable of doing.

While the 128K ROM might have been the "correct" way to do it, adding the 128K ROM is also arguably the "correct" way to add HFS support, and an external drive of any kind to the original Mac, not to mention that SCSI was a much more optimal format for the Mac than whatever the HD 20 drive is. However, that did not stop Apple from both creating the HD 20 and writing a software driver to use it with a 64K ROM. Wouldn't it have been easier to simply offer a ROM upgrade for the 512K Mac in September 1985 to allow the Mac to boot from the HD20, as well as natively use HFS? I think the "correct" answer is "yes". Morever this would fit with Apple's M.O. - how much more would power users have paid to get bootable ROMs for the HD 20? And then in January Apple could have released revised ROMs, with the 800K disk driver and SCSI, and charged those same users again for another ROM upgrade, which the die hard "brainwashed" Apple devotees would have happily ponied up for despite the price. Perhaps they could have avoided the 2 ROM revisions to fix the SCSI bug too.

As for being "completely pointless", that may well be in the real world, but as an exercise in vintage Mac tinkering, it has a much validity as any of the other proposed hacks on this forum. If Apple did it as an "official" solution to a similar problem in 1985, and John Bass did it unofficially, then it's just as valid an experiment today as it was back then, whether it is the "correct" way to do it or not.