Q's on 5200 controller specifics

[Viso]

I've been working on a gizmo to indirectly connect one or two unmodified Playstation controllers to an Atari 2600 and 7800. I'm having to redesign some of it, so I figured I'd try to support the 5200, too. But I need more information before I can get very far.

 

First: Joysticks

 

The schematics on the Atari Age site seem to be rather vauge on how the 5200 joystick inputs are handled. It looks like there is a 1.8K ohm resistor on each of the 8 input lines. As I understand it, a capacitor needs to be charged and the time it takes is used to determine the joystick position. The schematics show only two capacitors on the 8 input lines. That is two total, not per line. One is between the resistor and the POKEY, which makes sense, and the other is between the resistor and the controller. Both have different values.

 

What does the input circut really look like? The schematics show a circut that shouldn't work unless a voltage is used to determine the joystick position rather than a current. I'd really like to know the values of the resistors and capacitors involved, including the potentiometer in the joystick controller.

 

By contrast, the 2600 and 7800 schematics make sense. Except for the 2600A, they have 1.8K ohm resistors on the paddle inputs, and they all have 0.068uF capacitors between the resistor and the TIA. If I'm not mistaken, a 1M ohm potentiometer is used in each paddle. I thought the 5200 joysticks worked in much the same way as the 2600 paddles. Am I wrong?

 

Second: keypads

 

As the 5200 scans the rows of one controller, is it possible to tell which rows are being scanned on another controller without using the other controller's connection? My gizmo will only have enough input to see the row scanning for one keypad, and it would be nice to support two. So, are the same rows scanned on every controller simultaneously? Is it something like row N on one controller and row N+1 on the next controller to the right? Or is there no way to tell?

[DanBoris]

Joysticks:

 

Each pot input has an RC network (resistor/capacitor). There are two capacitors on each input. As you noted the schematic only shows two, but each one is labeled "TYP-8", meaning that the capacitor is repeated 8 times, once for each pot input. Each controller has two 640K pots which connect to the pot inputs, and also to an adjustible pot centering circuit.

 

Keypad:

 

The scanning circuit in the Pokey chip is switched to a specific port under software control, so if you are only connected to port 1 there is no way to see which of the other ports is being scanned.

 

Dan

[Viso]

Thanks Dan! Great answers.

 

Out of curiosity, is "TYP-8" a common thing to find on schematics?

[DanBoris]

The abbreviation "TYP" for Typical, is common on schematics. It is used to indicate a section of a circuit that is duplicated multiple times, but only shown on the schematics once.

 

Dan