From: Daniel O'Shea (dan_at_ozramp.net.au)
Date: 2007-04-11 06:32:18
thanks Jim & Levente, the ATmega8L looks like a good choice!
Jim Brain wrote:
> For the PWM code to work, you need 2 outputs for the POT lines, plus 1
> IRQ (can;t be on of the outputs) 3 pins
> 5 JOY buttons = 5 pins
I'm a little hazy as to how the IRQ works, I'd still want to have the
standard DE9 pinout as the interface to the C64:
1. Up
2. Down
3. Left
4. Right
5. Pot Y
6. Fire Button
7. +5V
8. GND
9. Pot X
...does the IRQ first read from the Pot lines, and then write to them?
> If space isn't a premium, I vote for the ATMEGA8, a 28 pin IC that has
> plenty of program space and IO for what you plan to do. It's $3.66 in
> singles. You can add some more goodies to the code later, if you wish.
Yes, I already have some goodies in mind for later... like maybe
adjusting the PWM for an Atari or VIC20, or maybe sending out button
presses as a NES/SNES compatible serial signal!
(PS. Jim, http://www.jbrain.com/ gives me an Error 403 - Forbidden?)
Hársfalvi Levente wrote:
> As of deciding which mode of operation should be the current one for
> the interface (C64 vs. PXA270): instead of jumpers, you can probably
> measure the supply voltage of the MCU right in the reset routine. All
> those Atmels have a built-in voltage reference... measuring the supply
> voltage by an ADC channel is fully possible. In the reset routine,
> your code could decide if the unit is powered from 3.3 or 5v, and set
> things up accordingly.
Yes, very good point - I had thought of that, but was worried about
accidentally sending 3.3V in to the C64! But I suppose it should be safe
if nothing is sent out until this check is done - would also be handy to
have the setup routine turn off the microcontroller's ADC Pot inputs in
3.3V mode, as they won't be needed...
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