7800 gamepad two-button option with the A8?

[walter_J64bit]

I know that you just plug the gamepad and just play your games as if it was a one-button but can the A8 be coded use the two-button option?

[Prodos8]

I think so, though I've never done it myself. Each button is connected to a paddle input, so pushing it is like cranking the paddle max resistance.

[Rybags]

I've tried mine (both) but no go.

 

Even tried the keyboard strobe method (like you're supposed to with a 2600 keypad).

 

Someone else might correct here, but it's a bit like button 2 on the ST mouse - uses the paddle input, but the resistor value isn't such that it registers differently on the A8.

[Prodos8]

Try using the paddle function in basic and see what values you get back when the buttons are pressed/released. I would but I don't have an Atari 8-bit computer. I think instead of high resistance, though, it goes to low resistance when the button is pressed.

[Rybags]

I've done that with both the ST mouse and the 7800 controllers. Nothing.

 

At the time, some searching revealed a "fix" for the ST mouse which involved changing a resistor value so that the second button would also work on the A8.

 

That makes me tend to believe that the 7800 sticks have some similar problem. Both my sticks worked fine on the 7800 last time I used them.

[+Philsan]

At the time, some searching revealed a "fix" for the ST mouse which involved changing a resistor value so that the second button would also work on the A8.

http://www.mathyvannisselroy.nl/stm18bit.txt

[Rybags]

That's the one.

 

If I remember rightly, the Amiga mouse was the same deal on the A8.

 

Searching around revealed nothing so far as fixes for the 7800 controllers though. Weird that Atari would make them such that you can't scan both buttons on the computer.

[Prodos8]

I'm going to try this out on my C64 once I locate the power supply. No paddle function in basic, so I guess I'll be looking up were in memory to peek for the values.

[+Philsan]

I'm going to try this out on my C64 once I locate the power supply. No paddle function in basic, so I guess I'll be looking up were in memory to peek for the values.

http://www.zimmers.net/anonftp/pub/cbm/man.../1351-mouse.txt

[Rybags]

On the C-64:

 

Paddles read from $D419/A (54297,98)

 

Problem is: you need to set Data Port A to which pair (ie - joystick port) you want. The OS strobes that port in the jiffy IRQ for it's keyscan.

 

But, you'd probably find it would work in one port or another (maybe).

 

PORTA is $DC00 - bits 7-6 (write) control which joystick ports to return paddle values for (01 =A, 10=B)

bits 4-0 return joystick 1 + trigger

PORTB is $DC01 - bits 4-0 for joystick 2 + trigger

 

 

I believe C-64 paddle reading works slightly differently in that: 1. They scan automatically, and faster (?) than the Atari

2. The values returned can range from 0 to 255.

Edited November 24, 2007 by Rybags

[walter_J64bit]

WOW, if this could be worked out just think of the new games that could use two-button option!

[mimo]

WOW, if this could be worked out just think of the new games that could use two-button option!

A proper version of Qix for a start

[Prodos8]

Well with the C64 its a no go as far reading the CX-24's twin fire buttons. I tried the following crude piece of code and all I got was a stream of '255' up the screen with buttons pressed or not. When I plugged in a set of paddles I could vary the value between 0-255 as expected. I guess I can understand now why it was not working on the A8 as the port is essentially the same as the C64's. Now I wonder how its done on the 7800?

 

You could make it work by tying the fire buttons to pin 7(+5v) and disconnect them from pin 8(gnd) & pin 6(fire). But that would require modding the stick. Interesting idea anyway.

 

5 poke 56320,64 : rem select pots on port a
10 ? peek(54297), peek(54298) : rem xpot, ypot value
20 for x=1 to 10: next x: goto 10

Well at least, after getting my C64 set up, I was able to test out my new CBM drives. The 1541 works fine, but unfortunately the 1571 isn't working it causes the computer to lock up and reset when plugged in.

Edited November 25, 2007 by Prodos8

[Rybags]

I tried the C-64 as well - no go there.

 

The pad uses a pair of 620K resistors (I think it was that value, it was just before bedtime I pulled it apart).

 

I'm thinking here that possibly lower value resistors might work? Although the worry always is breaking 7800 compatibility.

 

 

That 1351 mouse article is in no way applicable in this situation. It works totally different to an ST or Amiga mouse.

 

The ST/Amiga mice return an instantaneous bit pair for the X/Y positions of the mouse, where the 1351 returns a delta value over the paddle inputs.

[Heaven/TQA]

what about the genesis pads?

[Rybags]

No idea - from what I've read in the past, I think they have to be modded as well for the extra buttons to funtion on an Atari.

[+CharlieChaplin]

Well,

I have a Sega Mega Drive / Genesis 6-button pad (actually 6 buttons + left/right finger trigger) connected to my Atari XL. Fire button "B" works as the Atari firebutton. Afaik, there is already the game "Gem Drop" by Bill Kendrick available that supports two buttons of the 3- or 6 -button Sega pad on the Atari...

 

So, there is probably no need for modification of the Sega pads. Alas, I also have a third-party 3-button pad for the Sega, it works well on the Sega, but to my surprise not so well on the Atari XL (the directions work, but none of the fire buttons work on the A8)... -Andreas Koch.