Ideas for a new Apple I

5 replies [Last post]
cbmeeks's picture
Offline
Joined: Jan 17 2005
Posts: 56

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?

Thanks

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.
Offline
Joined: Jun 5 2008
Posts: 380
Re: Ideas for a new Apple I

You should check your out the brain board documentation and firmware for one way around your dilemma.

Regards,
Mike Willegal

Offline
Joined: Oct 9 2011
Posts: 1045
Re: Ideas for a new Apple I

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...

  • USB Keyboard, PS2 are getting hard to find.
  • Forget the whole run it off a USB adapter thing, it's worth using a wall wart to have a built in ACI. FYI: The trick of using ground instead of -12 for the cassette adapter isn't reliable with the noise an EEPROM puts on the bus. This is something that Vince found out when trying to make his own ACI. So use an ICL7662 to invert wall wart power to -12V and a simple 7805 for the main board to make 5V.
  • Have a soft reset option to trigger the reset and clear screen using the keyboard. Makes it easier to put the board in a case.
  • You can drop the Apple II keyboard socket, its not worth wasting an Apple II keyboard, they are too expensive now.

CWJ_Wilko's picture
Online
Joined: Jun 3 2015
Posts: 272
Re: Ideas for a new Apple I

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

cbmeeks's picture
Offline
Joined: Jan 17 2005
Posts: 56
Re: Ideas for a new Apple I

@Corey986

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. Smile

2) And extra VIA or two for I/O.

3) 32K RAM

@CWJ_Wilko

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.

evank's picture
Offline
Joined: Jan 30 2005
Posts: 48
Re: Ideas for a new Apple I

@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.

__________________

@ Director, Vintage Computer Federation, a 501(c)3 non-profit -- www.vcfed.org
@ Author, "Abacus to smartphone: The evolution of mobile and portable computers" -- www.abacustosmartphone.com
@ Homepage: www.Snarc.net