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Topic: Elppa I: An Apple I clone (Read 3309 times) previous topic - next topic

Elppa I: An Apple I clone

Hi Guys,

I'm starting work on an Apple I clone I call the Elppa I (Apple spelled backwards). I'm hoping to sell a few completed units. I'm starting a blog at elppa dot c o m. (Won't let me post URLs) Check it out and let me know what you think!

Adrian Sarli

Re: Elppa I: An Apple I clone

Reply #1
I am very very excited to see what you will do for the apple clone, and hopefully it will include LOTS of pictures! :P

One thing though if I may suggest, don't do all your write up on your blog and leave just one post here saying that it is on your blog. I was once tempted to do the same thing, but I realized that it is like self advertising on this forum and not what this forum is meant to do.

Instead I just use my webserver to host the pictures, putting less of a demand on dangerous prototype's bandwidth, and link my website back to dangerous prototypes. Eventually I will make a small photo gallery on my website for each project with a small write up, but the forum will be the majority of where the content will be.

Re: Elppa I: An Apple I clone

Reply #2
Oh wow, you can still buy those meaning they still manufacture them, or they are available to buy on eBay and things like that?
From my understanding most microprocessors from that time are no longer manufactured, but some (like the 8051) are being sold in terms of the IP to ic vendors for use in their ic's, like atmels AT89LP, but the original 8051's are no longer available from manufacture.

Re: Elppa I: An Apple I clone

Reply #3
I did see the FPGA Apple II clone, but I've settled on using a WDC chip because I don't have experience with FPGAs (though that is on my list of things to do).

The WDC chip is still in production, and from some communication I've had with them, they are still actively developing products.

I'm planning to use microcontrollers heavily to eliminate as many parts as I can. Given that a PIC24FJ64GA002 is available for about $3 and runs at 16 MIPS, I think this will prove economical.

Re: Elppa I: An Apple I clone

Reply #4
Though I don't have any experience with CPLDs, they appear to be the cheapest (and best) way to go. I guess I'll order a dev board. Which one should I get?

Re: Elppa I: An Apple I clone

Reply #5
Hmm... Can a CPLD have 960 bytes of RAM required for the video buffer? Maybe I should use a CPLD for glue logic/keyboard/replacing the 6821, and a PIC for composite/BW video output.

Re: Elppa I: An Apple I clone

Reply #6
A big CPLDs can hold the whole thing, ram and all. I guess that was already mentioned. You need a big one though 1024+macrocells. FPGAs are "cheaper" for RAM parts IMO.
Got a question? Please ask in the forum for the fastest answers.


Re: Elppa I: An Apple I clone

Reply #8
You can also use a propeller for video generation, it generates direct NTSC if you want. It was actually designed keeping video generation in mind! It is only $8.00, and can do 160 Mips

http://www.parallax.com/PropellerChips/ ... fault.aspx
http://www.parallaxsemiconductor.com/si ... v1.0_0.pdf <-- good examples for video generation.

Re: Elppa I: An Apple I clone

Reply #9
I am keeping the propellor in mind, but I really want to see if I can squeeze acceptable video generation out of a PIC. I've been having some modest success so far. Maybe I'll post some pictures on Sunday.

Re: Elppa I: An Apple I clone

Reply #10
What resolution and refresh rate are you aiming for? Your success might be limited because the PIC24FJ64GA002 does not have a DMA and runs at only 16 mips, may I suggest getting the pic32MX220F032B? It has a full blown DMA and runs at 40 MIPS, so getting video out of these guys should be easier if you run into a major roadblock. :P It costs 2.89 off microchip direct, and it comes in a PDIP variant, though the only problem is that you need a pickit3 instead pickit2 or a jtag programmer. Currently I am working on getting the bus pirate to program one of these guys so if I make any progress I can put the info here if you wish. :P

Some of us here are familiar with assembly so you can post up your code and we can try to squeeze some more out of it if you need help!

Re: Elppa I: An Apple I clone

Reply #11
Here's a picture of the video circuit:


I'm using a PIC24FJ64GA002 for testing. I need ~240 pixels for a 40 character display. (That's what the Apple I used, so to be true to detail, I'm thinking of doing that.) According to http://http://www.stanford.edu/class/ee281/handouts/lab4.pdf, (which I assume to be reliable) I have 51.5 uS to display the 240 pixels. If I run at 32 Mhz--16 MIPS, I will be able to execute 824 instructions during the visible portion of the line. This would give me 3.433 instructions per pixel. I can do some prefetching during the horizontal and vertical syncs.

I'm using a PicKit2 clone currently. I don't have the BusPirate programming adapter. (I think Ian is ordering more? If so, I'll probably buy one.) How similar is PIC32 assembly to PIC24 assembly? I could probably cook up uses for that extra speed--especially at that low price. (USB keyboards, for example.)

Re: Elppa I: An Apple I clone

Reply #12
You wont find any CPLDs in the 1k element range that aren't +3.3V or less and SMT.  So given that, I would recommend looking at a MachXO2 from Lattice.  It's hard to beat the combination of features and price.  You can get an eval board for as little as $29 direct from them.  And like with Altera, Xilinx, Actel and others, the development and synthesis software is free for small to mid-range devices.