A few weeks ago, Ben Heckendorn presented a couple of episodes of the
Ben Heck show in which he built an Apple-1 replica. It's not clear what he used as the schematic and he built his electronics on perfboard, but there are many hints that he used the
Brielcomputers Replica-1 as the basis for his design: he used a Propeller for the video, a PIA to connect the Propeller to the 6502, a static RAM chip, and an EPROM.
One of the remarks he made in the
second episode of the
three-show project was something like: "The Propeller could replace the PIA if you would program it in Assembler". If you follow me on
Google+, you already know that
I created an Apple-1 replica with my
Propeddle project earlier this year, so I already have the assembler code to do that. I also
worked with Vince Briel on his
Superboard project, so I had some code to let the Propeller emulate ROM and RAM. So I wondered: how hard would it be to strip down my Propeddle design and create a simple schematic with just a Propeller and a WDC 65C02, without the glue logic and without RAM or ROM chips, to replicate small simple computers such as the Apple-1, that don't need IRQ or any of the other signals.
As it turns out, that wasn't hard at all.
I had an old USB Proto board from Parallax (#32812) in my parts drawer, and they can't be used for making a Propeddle clone because the Propeller is in the middle of the PCB and doesn't leave enough space to put the other components on there.
Parallax don't sell that particular board anymore, but a similar board that has a Propeller Plug header instead of a USB port is still available as
#32212. They also have the
#32810 which has the Propeller on the side and therefore leaves a lot of space for components (I made a
wire-wrap version of Propeddle on one of those). Anyway, I soldered a 40-pin socket onto my proto board so that the D0-D7 data bus pins lign up with the P0-P7 pins of the Propeller, and wired up the other connections in less than an evening. Then I converted my Apple-1 replica software from Propeddle into a new Github repo at
https://github.com/JacGoudsmit/L-Star.
Attachment:
File comment: The top side of the PCB. The video output and keyboard input are optional: the Apple-1 works like a terminal so you can just use the serial port instead.
2014-12-13 10.52.42-small.jpg [ 1.12 MiB | Viewed 969 times ]
I took pictures while I was wiring up the PCB but unfortunately I made a few mistakes while I did this, so the pictures are unusable. But I got it to work as an Apple-1. The attached picture shows it running the "30th anniversary demo" for Apple-1 that I found online somewhere. I also played Star Trek and other BASIC games on it.
Attachment:
File comment: L-Star running the Apple-1 "30th anniversary demo" showing the picture of Woz in glorious ASCII definition :-)
2014-11-28 23.59.22-small.jpg [ 1.05 MiB | Viewed 969 times ]
I'm currently away from home on a business trip, and I took the hardware with me, so that I could spend some spare time creating an OSI Superboard II emulator. Unfortunately my hardware stopped working so I'll have to build another one and that's not going to happen until after Christmas, probably not until the beginning of 2015. This time I'll take more pictures and I'll make sure I don't make mistakes so I can post a how-to on Instructables or here in the 6502 forums or on the Propeddle website or on the Parallax website or
hackaday or...
For now, if you want to build one yourself, go to the
Github repository and read the ReadMe. There are schematics and even a rudimentary PCB design (in Kicad format) if you want to build one from scratch, but it's probably easier to get a Parallax proto board and put the 65C02 on it. If you have any questions, post them here. Thanks for watching!
===Jac
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