Re: Apple II Pi

[David Schmenk <dschmenk@gmail.com>]

On Thursday, 23 May 2013 17:58:45 UTC-7, Michael J. Mahon  wrote:
> David Schmenk <dschmenk@gmail.com> wrote:
> 
> > This weeks project:
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> > 
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> > http://youtu.be/Kx_ggKHWaxA
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> 
> 
> Dave,
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> 
> 
> You can probably use the RPi GPIO pins to eliminate the need for a serial
> 
> link...  It shouldn't take more than an octal transceiver connected between
> 
> the RPi and the Apple bus--controlled by the Apple bus. 
> 
> 
> 
> -michael - NadaNet 3.1 and AppleCrate II: http://home.comcast.net/~mjmahon


The RPi GPIO pins really aren't as powerful as you might think.  The choice by the Raspberry Pi foundation as to which pins to bring out to the header, was, um, a little odd.  Once I gave in to using the serial interface as the communication channel and using the 6502 to do the dirty work, it actually made things much easier.  For one, it's pretty hard to service interrupts for the Apple Mouse remotely.  As I'm running the serial link at 115K and the communication traffic is pretty light, performance isn't much of an issue.  I would like to add the ability to read and write Apple II memory from the RPi, as well as call code on the Apple II - kind of like a retro Arduino.  My thoughts on the IIe expansion card are to use a 6551 (same as the SuperSerial Card) but derive it's baud rate clock from the RPi's GPIO general purpose clock pin (thus saving a crystal).  Also connecting one of the GPIO pins to the 6502 RESET line would allow the RPI to reboot the Apple II if it hung.  Then we could play with the Apple II's I/O bus from Linux.

Dave...