Mac SE FDHD ROM / SWIM PROM clones?

[clh333]

Is there an EPROM / EEPROM which has the same pinout and capacity as the Macintosh's masked ROMs?  I would like to copy my FDHD's ROMs and equip another SE with FDHD capability.  Aside from the MFM 1.4 drives, I believe these are the only differences between the machines.  Am I correct?

-CH-

 

[Themk]

Sorry, but you can't just copy the FDHD ROMs over to get SuperDrive capabilities! You have to have the Sandberg-Wozniak Integrated Machine chip in order for MFM formated disks to work. You need the drive + floppy host controller (SWIM) + ROM in order for it to work.

Sorry. Also, the SWIM chips are hard to find just on their own, but you may find a FDHD upgrade kit somewhere, who knows.

 

[avadondragon]

The SWIM is not a ROM so it can't simply be copied with a PROM burner.  You must duplicate the logic inside the thing and then replicate it in a custom logic device.  I once had the fantasy of reverse engineering the SWIM chip and recreating it in a cheap PLD.  Seemed like something fun to put my FPGA project board to use on.  I gathered up a ton of technical documents on it but then I mysteriously discovered an FDHD buried in the woods and stole its ROMs and SWIM chip so I lost interest in the idea.  In theory someone that had a good understanding of how the SWIM chip worked could do it.  Maybe the guy over at BMOW who made the Floppy Emu could do it?

If you steal a SWIM out of another Mac (and it's floppy drive) you can copy the ROM from the FDHD and make that work.  There are different versions of the SWIM and a couple different packages for the original SWIM.

 

[Themk]

I have a nice technical listing of the SWIM chip sitting on my hard drive, thought about doing a design, maybe it has the schematic in the back of it? Its like a 200MB PDF document.

 

[clh333]

Thanks for your replies.  Today I located a PDF of SwimChip User's Ref, copyright 1988 from Apple.  There was enough technical detail in the document to let me understand that the IWM and SWIM (they refer to it as ISM) are both dedicated controllers, along the lines of the Zilog or NEC chips, rather than ROMs.  Somehow I got the misperception that the Sony drives were doing most of the controller's functions.

I understand the difference between the GCR group coding employed by the IWM and the MFM coding used by the SWIM: both are a form of RLL encoding designed to compensate for the signal format and timing issues inherent in communicating with disk drives - especially floppies.  I also understand that the 800k Sonys vary track density by spinning the disk at different speeds when the head is in different zones of the disk, while the 1.4M drives are constant-speed.  Constant speed and MFM encoding make them compatible with IBM's format.  So the SWIM has to be able to handle either type of drive, and by extension, either type of scheme.

Obviously the drive is responsible for identifying the type of disk currently inserted.  I would assume the controller (i.e.IWM/SWIM) receives this information from the drive and passes it along to the ROMs, but that's just a supposition.  But to return to my original idea:  It is not possible to "upgrade" an SE to an SE FDHD by copying the three chips of an FDHD that serve as ROM and disk controller.  It appears that it IS possible to "swap in" these chips on an SE motherboard as the pinouts are the same for both machines.  Provided that the machine is also equipped with a Sony 1.4M drive it will then function as an SE FDHD.  Is this correct, or is there another factor that I'm missing?

Lastly, there were several different form factors and more than one functional variants of the SWIM chip, but the basic dual-density functionality is contained in the 28-pin DIP.  Cloning the ROMs is a much less formidable task than duplicating the function of this chip.  For now, that means cannibalizing existing equipment.

-CH-

 

[avadondragon]

You seem to have a very good grasp of the situation now.

The ROMs are easy enough to copy (you could probably even find an FDHD ROM dump onine) if you can get another SMIW from somewhere and Sony floppy drive then you'll have yourself an upgraded SE FDHD.  I did exactly this on my own SE.

 

[techknight]

If you have a PLCC to DIP adapter, you could steal a PLCC version of the SWIM from another machine, like a battery blown one. 

 

[Trash80toHP_Mini]

That'd be your FDD donor as well, got linkage for that adapter?

I'll be looking at the DevNotes on my DOA system boards for Macs with discrete SWIM IC's. IIRC its function was rolled into ASICs at some point so the donor list would be good to post here if someone wants to put one together.

 

[clh333]

I have extra Sony drives 800 and 1.4.  I have a PROM burner.  I have extra SEs that I could "convert".  But I only have one SE/30 and one SE FDHD, both working.  I purchased the SE FDHD as a "project" which supposedly had "issues" but the damned thing runs like a top, so I'll have to keep looking for a donor.

-CH-

 

[CC_333]

What kind of logic does the SWIM use? Someone should try to clone it....

Of course, it is probably prohibitively difficult/impossible, as I'm sure someone would've done it by now if it weren't.

On the other hand, nobody here ever thought (to my knowledge) that custom ROM SIMMs were possible until doug3 invented them, or that the HD20 could never be emulated (until BMOW reverse engineered the HD20's protocols and successfully emulated it) so perhaps it'll be done eventually.

c

 

[Trash80toHP_Mini]

Or somebody might ask the Woz if he's got any documentation on his masterpiece?

 

[Themk]

I found a boatload of information on the SWIM, ISM, IWM

Lots of PDFs which have lots of pages here:

http://dec8.info/Apple/Apple%20Floppy%20Notes/

 There are goodies like "ISM ASIC Spec", "IOP SWIM Driver ERS", "IWM Design Spec", SWIM Chip spec, SWIM Users Reference... and more

 

[360alaska]

If you have a PLCC to DIP adapter, you could steal a PLCC version of the SWIM from another machine, like a battery blown one. 

I did something like that in my conquest thread:

https://68kmla.org/forums/index.php?/topic/25854-alaskas-collection/

 

[Trash80toHP_Mini]

Fabulous work in that thread, surprised I missed it.

 

[techknight]

Because its in the wrong forum

 

[Trash80toHP_Mini]

You mean like this hacks thread?