Hello. I'm new at this, so here goes:
I'm really interested in building a computer based on the 6502 similar to an Apple ][. I don't have the foggiest idea where to find the schematics necessary, or quite where to start. I really could use some help! Thanks!
A.S.

The most straightforward way is to buy a copy of the old "Aplle II+ Technical Reference Manual" which came with all of the Apple II+ computers ever sold, so there are still a lot around in the back dusty shelves of used computer stores. Also check out swap meets, Goodwill, and Salvation Army store bookshelves.

This book not only has a complete schematic including the video generation circuitry, it also has a complete listing of the firmware (monitor ROM) and some pretty decent descriptions of how everything works.

If you can't find it anywhere, post a reply or E-mail me directly and I will try to scan in my copy -- but it is fairly large so it will have to be done in sections.

-- Brian Farley

It's likely that the reason you want to make a copy of the Apple][ because you don't have one. It would be easy enough to get one for the cost of shipping if you simply put out a call in a few newsgroups.

Also, if you'd had one back when they were mainstream, you'd really want something a bit less restrictive. IIRC, the ][+ had three segments of memory dedicated to display refresh right in the middle of everything else. Also, not only does the processor run at somewhat less than 1 MHz, but it has wierd timing to make it easier to generate the video control strobes.

The text display memory was inconveniently located, kind of like the PC video memory, but much more so. As a result, APPLE][ applications had to be loaded at $0800 because the text memory was in the space below that. There are all sorts of oddities like that in the ][/][+

If you want to build your own, yet don't want to write all the code yourself, perhaps what you need to do is look at the software you want to use, and configure your system so it runs that.

I'm a believer in one RAM, one ROM, one CPU, and I/O where it's needed. What that means is that you can build a system with one 65kx8 ram device and one 64kx8 EPROM, and one processor, and you're done, except, of course for the I/O that you need in order to use the thing. You can make the I/O device selects "or'd" so they disable memory, hence can coreside with memory. The ROM is read at power-on, written directly back to RAM, and then disabled, which can also serve to increase the clock speed. Once you're that far along, all you need is to decide what you want and add it. As I said, you OR the enables to the I/O devices so they don't contend for the bus. A GAL or a 74HC133 can do that for you. (It's a 13-input positive-input NAND, hence, it's a 13-input negative-input OR.)

If you use your imagination, you can easily take several peripherals and address them wherever you like, and, in fact, change that under software control.

Uli

It would be interesting to build a clone of the Apple II...then again, while the monitor and most of that stuff is open source (!) the BASIC does not appear to be (well go figure, Microsoft wrote the first version) ^_^,,,

The IIc was essentially a clone of the II+, with most of the random logic implemented in a couple of gate arrays.

I've seen a couple of instances that used the "Applesoft" BASIC on non-Apple computers. Apparently, given enough knowledge about what it does and what system support it relies on, it's quite portable. I once used it on a clone of a Digital Group computer, running an operating system called APEX from 8" floppy disks. It seemed to work OK.

BTW, I was under the impression that Microsoft didn't actually write the Apple BASIC. I was told, though not necessarily persuaded, that a small company called Applesoft created what then was a near clone of the Microsoft BASIC for the Z80. It was a couple of generations behind the Z80 version, but, nevertheless, quite useful.

Uli

Microsoft BASIC ran the C64 (see the boot copyrights on some versions of the ROM: (C) 1977 Microsoft Corp.) and Applesoft BASIC had similarities to C64 BASIC that it did not have to GW-BASIC (which was essentially a port of Z80 BASIC to the PC with enhancements). And the Laser 128...

There's detailed history of the evolution of the various dialects of BASIC used on microcomputers over the mid-70's through mid-80's. I don't have it, nor do I know where it resides these days, but I don't think it's terribly important at this stage. It does come up in some of those senseless arguments about Bill Gates' life story, etc.

Love 'em or hate 'em, the Microsoft boys started the BASIC ball rolling with their Altair BASIC, and the fact that they were seemingly copied several times simply suggests that they did a good job. Remember, Microsoft didn't invent BASIC, they just invented the Altair BASIC, later to become MBASIC and later a couple of other dialects.

Uli