Re: Commodore joystick ports

From: Daniel O'Shea (
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, 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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