When I first heard about the Replica One, I was jumping for joy. I thought that was the coolest thing ever. I bought the Building the Replica One book (first printing) with the hopes of one day building it.
I also always planned to buy the Replica One kit from Briel but couldn't justify the cost at the time. Well, a DECADE later, I decide it's finally time to buy the Replica One. Now, as luck would have it, it seems Vince has gone off the grid with regards to building/selling these kits. This is my fault for waiting so long.
Anyway, the second reason for buying that book was to learn enough to build my own 6502-based computer. So I thought...why not build a "Replica One" replica? A replica of a replica! LOL
But seriously, I am designing a 6502 computer that, I would hope, would be mostly compatible with the original Apple 1. Now, here's the deal...I have several ROM's that I would like to load on it. Some that won't fit into the 8K that Vince's design uses. In fact, my design uses 32K RAM and 32K ROM (minus a little RAM for I/O).
Now, I see a few problems with this.
1) The PIA address space for keyboard / display of $D010-D013 is in conflict of my 32K ROM.
2) The $E000-$EFFF RAM space is in conflict of my ROM based on a memory map that I read:
"RAM space available for a program in an 8K system modified to use cassette BASIC"
3) A few addresses in the $CXXX space for the cassette interface. Believe it or not, I actually want to support the cassette interface.
As you can see, my 32K ROM is just going to be out of the question if I want to maintain this address space and NOT use something like CPLD/FPGA for advanced memory decoding (I don't want to use programmable logic).
So, what are my options? I suppose I could recompile the Woz mon (for example) to use a different address for the PIA. But that would probably break a lot of legacy code.
I guess the question comes down to how much Apple 1 compatibility I want vs. how much of a general purpose 6502 computer I want.
What are your opinions?
You should check your out the brain board documentation and firmware for one way around your dilemma.
I think it's a great project to do. You should try to make it as compatible with the Apple-1 as possible, but include a cassette interface (ACI). You can drop all the circuitry for the LED signal indicator on the cassette interface to simplify it.
Since Vince has disappeared from making the Replica-1, I think the appetite for a simple Replica-1 type system has built up. If you could fix the minor things about the replica-1 that sucked it would be great and then you could even sell a blank board with EPROM to help finance your project.
Things I would fix...
When Vince went off the grid I tried (and failed) to build his original Replica 1 from scratch, as it was the only version I could find with complete documentation.
I was thinking about purchasing an L-Star, which is a very simple Apple 1 replica, it can even be assembled from scratch on a breadboard. It could be a place to start: https://hackaday.io/project/3620-l-star-software-defined-6502-computer
Those are some great ideas!
Some ideas that I would remove from my version of the Replica One would be:
1) Remove ATX power supply support (I think I could get the other voltages someway else if I *HAD* to have them).
2) Use a standard wall-wart DC power supply for the board. Also, provide a two-pin header (or maybe JST) so that it could be mounted in a case.
3) Remove ASCII support. This is really nice. But who can afford these anymore even when they do show up!
Some ideas I would like to add:
1) VGA support. Even if monochrome. NTSC would still be nice to support if you wanted. But I have a 14" VGA monitor that weighs about 5 lbs and takes up very little space. Would love to use it instead of my beefy 1084S.
2) And extra VIA or two for I/O.
3) 32K RAM
I can personally recommend the L-Star. Jac is a very smart guy and his board is a joy to use. I have one of his first runs (not the Plus). In fact, it's about as close as you can get to a Apple One that is still made and affordable.
The only reason I want to build my own (other than saying I built my own) is that I don't want to emulate the glue, RAM, etc. His implementation is awesome. Just a different direction I want.
@CBmeeks I share Corey's enthusiasm for your project. Good luck with it!
>> I can personally recommend the L-Star. Jac is a very smart guy and his board is a joy to use. I have one of his first runs (not the Plus). In fact, it's about as close as you can get to a Apple One that is still made and affordable.
I'm not very familiar with the L-Star but the Mimeo kit is much closer to being a "real" Apple 1 and it's relatively affordable.