Re: Apple II with ATMega (was Re: Apple II Pi)

[David Schmenk <dschmenk@gmail.com>]

On Monday, 3 June 2013 17:59:27 UTC-7, Ralph  wrote:
> Thanks for posting this.  It's fun to see folks hooking their Raspberry Pi systems to the Apple //.  
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> 
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> I'm (slowly) working on something similar, except with the Propeller or ATMega/Arduino chips.  I think the ATMega would be a better I/O processor for Apple // connections, compared to the Raspberry Pi.
> 

Actually, I'm using the Apple II as the I/O processor for the Raspberry Pi.  I find it's much easier to interface real world devices to the Apple II, either through the game port or through a proto-board/breadboard.  I don't find the 3.3V low power I/O of the RPi, or the Aurdino for that matter, as easy or robust as good 'ol 5V TTL.  Of course the Broadcom part in the RPi and the ATMega in the Arduino were meant for very low power applications, so it makes sense that they were designed that way.  Kind of like the difference between a big block V-8 and a high-strung 4 cylinder.

>  
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> I'm considering a 74LVC244 or 245 chip to use as a bus transceiver, to convert from 3.3V to the 5V used by the 74LS TTL levels used by the Apple //.  Finding a cheap source for DIP versions of those chips would be helpful, since I'd prefer not to spend more on logic-level conversion than the micro-controller itself.

I'm going to be experimenting with that myself.  I'm going to interface a 3.3V serial port to the 6551.  I hope I only need a voltage divider from the 6551's Tx to the BCM's Rx line.  Then I hope to power the 6551's crystal input directly from the GPIO GCLK. Fingers crossed.

Dave...