LCIII EPROM?

[frontein1]

Curious if anyone has tried replacing the stock LCIII ROM ICs with EPROMs? I'm thinking something along the lines of the 27C400, but I am trying to do a pin-by-pin comparison right now.

Has anyone done any research on this before? And if so willing to share?

 

[finkmac]

not much to research. you can replace any mac [P]ROM with an EPROM or EEPROM equivalent

 

[Boctor]

This research (authored by a user here!) helped me figure out which ROMs were compatible with my IIcx and IIci, and gave enough introductory info to help me replace my failed mask ROMs with cheaper flash ones... After a bit more help from other users here, who alerted me to the obvious but easily-solved pitfall I forgot about: Common flash chips like the SST39SF010 need the Write Enable pin to be high when in the Mac, to enable reading. Other than that, they're perfect.

 

[frontein1]

Thank you @finkmac and @Boctor!

Have the ICs and programmer in the mail. Looking forward to having some fun with the LCIII that I originally purchased from @jmacz.

 

[jmacz]

Thank you @finkmac and @Boctor!

Have the ICs and programmer in the mail. Looking forward to having some fun with the LCIII that I originally purchased from @jmacz.

Nice, have fun!

 

[finkmac]

Thank you @finkmac and @Boctor!

Have the ICs and programmer in the mail. Looking forward to having some fun with the LCIII that I originally purchased from @jmacz.

consider investing in an EPROM eraser too!

protip: the phone sanitizers with UV bulbs (not LEDs) work VERY well.
they can also be had fairly cheaply and are generally higher quality than the generic "eprom eraser" deathtraps you can get on amazon and such.

 

[frontein1]

consider investing in an EPROM eraser too!

I went with the GQ-4X4 from MCUMall. Also with the appropriate adapter and UV eraser. I'll report back on how that bundle works.

Interestingly, I took a closer look at the board, and I noticed that the ROM sockets are actually 42-pin each even though the ICs being used are 40-pin. I pulled up the Apple Developer Notes and Bomarc schematics. I am wondering if these are tied to additional address lines, and if so, perhaps I could expand the ROM to 4MB with room for a built-in ROM Disk.

 

[finkmac]

this guy? i wouldn't use those, they're AC wall power direct to the UV bulb. simple, but potentially dangerous...

 

[dougg3]

I am wondering if these are tied to additional address lines, and if so, perhaps I could expand the ROM to 4MB with room for a built-in ROM Disk.

They are. They go to A20 and A21. I haven't tried it myself, but it should work. I'm not sure if you would need to do any MMU reconfig like what was required for the Quadras, but it should be possible to get 4 MB of ROM in the LC III.

 

[frontein1]

They are. They go to A20 and A21. I haven't tried it myself, but it should work. I'm not sure if you would need to do any MMU reconfig like what was required for the Quadras, but it should be possible to get 4 MB of ROM in the LC III.

Looks like I've identified my MARCHintosh project for this year!