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A Few Lisa Things I've Been Working On

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AlexTheCat123:
Over the past several months, I've been designing and reverse-engineering a few boards for the Lisa and I can finally share my results now that I'm done.

First up, I made replicas of the 2-port parallel card and the 2/5 motherboard that are as similar to the originals as possible. I actually put these on GitHub a month or so ago, but I realized that I forgot to make a post on here when I did!

After the intellectual property discussion on here about reverse-engineering the Sun SCSI card, I decided to just make my own version that consolidates the glue logic into a GAL16V8 and that swaps the EPROM out for an F-RAM that can be reprogrammed without having to remove it from the Lisa. Hopefully that last feature makes it easy to write code for expansion cards! I originally wanted to use a 28C64 EEPROM instead of the F-RAM since they're a bit cheaper, but the write time of 5ms was just too slow.

For practice with 68K assembly, I also ended up writing a little program that lets you write a 4K ROM image from your modern computer straight into the expansion card F-RAM over serial. It's really simple, but also really useful!

I also adapted this program to let you load code straight into the Lisa's RAM over serial to speed up software development. It's sort of like the BLU serial bootstrap program, except that you don't have to hard-code the size of your program and it automatically jumps to your code after a one second timeout of not receiving any data from the serial port.

I'm not sure how useful some of these tools would be to people (the PCBs are probably way more useful than my assembly language programs), but I figured I'd share everything anyway.

Let me know how all this stuff looks and if you guys have any suggestions for potential future revisions!

rayarachelian:

--- Quote from: AlexTheCat123 on July 11, 2022, 05:59:01 pm ---Over the past several months, I've been designing and reverse-engineering a few boards for the Lisa and I can finally share my results now that I'm done.

--- End quote ---

Well done good sir; if I may "Meow" to you.

stepleton:
Wow, congratulations on these developments!

I am a little embarrassed to say that I had never heard of F-RAM before. The very distant similarity to magnetic core clearly makes this a technology of choice for retrocomputing projects  :D

One of the biggest problems I've had with making Lisa expansion cards is just getting the size of the card right. Kudos for this feat alone; if you find that your cards fit correctly, I'll happily revise to your measurements. In general, this all looks like it must have taken tons of time!

D.Finni:

--- Quote from: stepleton on July 11, 2022, 08:15:45 pm ---I am a little embarrassed to say that I had never heard of F-RAM before.

--- End quote ---
Well don't be, because you could be like me: I post fairly regularly here, but I have never seen an Apple Lisa, much less even used one.  :o

AlexTheCat123:

--- Quote ---Well done good sir; if I may "Meow" to you.
--- End quote ---

--- Quote ---Wow, congratulations on these developments!
--- End quote ---
Thanks! I'm glad you guys like them!

--- Quote ---I am a little embarrassed to say that I had never heard of F-RAM before.
--- End quote ---
Don't be embarrassed; I hadn't heard of F-RAM chips either until Ray suggested them to me! They're really cool and useful!

--- Quote ---One of the biggest problems I've had with making Lisa expansion cards is just getting the size of the card right. Kudos for this feat alone; if you find that your cards fit correctly, I'll happily revise to your measurements. In general, this all looks like it must have taken tons of time!
--- End quote ---
I know what you mean; it took a lot of work to get the card size just right. They seem to fit really well, so feel free to revise your design if you want! And yes, all of this took several months to complete (although I wasn't working on it nonstop).

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