Re: Commodore joystick ports

From: Jim Brain (
Date: 2004-10-23 22:42:03

Just a short note... Hársfalvi is my lastname... so, just in case you 
intended to call me by my firstname, you should call me "Levente" ;-).

Many apologies. The last_name first_name thing is hard to discern from 

> The 10 cycles delay is introduced by the 10k resistor. I used it 
> mainly for safety reasons and compatibility (the 1351 had 5.1k, but 
> due to the 5717's outputs having greater resistance than the PIC16c84 
> outputs, I raised it to 10k to meet similar delay in overall). Though, 
> I haven't investigated this further. In theory, you could completely 
> omit the resistor; after that move, the minimum value (read from the 
> SID registers) is a function of

I tried that last night, but if the resistance is < 3k, the 
uController's ability to source is more powerful than the SID's ability 
to sink, so no falling edge is seen, so the unit does not work.  
However, at 3k, I can get down to "4".

> Actually, you could use the Atmega8's internal RC oscillator (in case 
> you're experimenting with a 'mega8 ).

I have one here, but was using a 16 for initial tests.  However, I'll 
try the 8 I have.

> The biggest problem -- if I'm correct -- won't be the protocol itself, 
> but the interference with keyboard activity. ...But I may as well be 
> wrong in this.

My protocol idea assumes you don't scan the keyboard rows during the 
time you request raw data.


Jim Brain, Brain Innovations                      
Dabbling in WWW, Embedded Systems, Old CBM computers, and Good Times!

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