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Jope · 30 August 2013, 12:13

There has been a lot of discussion about using Sega Megadrive/Genesis pads on the Amiga.

It seems the Paula pin servicing the controller port pin 5 can handle the current drawn from it, since it's designed to handle being shorted to ground by a middle mousebutton. Unmodified pads shouldn't burn anything in the Amiga.

One reason to do the modification is, that the Amiga cannot control the multiplexer inside an unmodified Megadrive pad, thus you will only be able to use two of the fire buttons. Pin 7 low = A+Start are readable, Pin 7 high (locked to this state in an unmodified pad) = B+C are readable.

Don't connect them to a C-64 without doing the 5<->7 swap. The circuit is different in those.

The following is recorded here for history's sake, make of it what you will.

Many people have noticed that they seem to work just fine unmodified and have no second thoughts about it.

However you should be aware that there are a few things to understand and after that you can make the decision whether to keep on using the unmodified pad, or to do something about it.

The difference is that on atari sticks the +5V supply[1] is on pin 7, and on the megadrive, pin 7 is a signal pin instead[2].

So why you shouldn't just plug in a megadrive pad into an Amiga unmodified? If the POTGO register has been configured to set pin 5 of the joystick port as an output with the value 1, you are driving the megadrive pad's power supply from a signal pin and you might fry the signal driver in your Paula.

To be safe, you should either make an adapter that passes all other pins through but crosses 5 and 7, or modify the megadrive pad itself, by desoldering these two wires from the circuit board and reconnecting them in each other's place.

This goes the other way if you have a USB -> Megadrive pad adapter and connect an Atari joystick to it, you're driving the Joystick's autofire circuit's Vcc with the megadrive adapter's pad duplex select signal instead of an actual power supply line (which would be on pin 5 for the megadrive).

Sure, it might work forever if you're lucky, but then again it might burn out the driver for that signal at the controller chip inside the USB adapter if you're unlucky. Then you can't use megadrive pads with the adapter any more.

[1] http://old.pinouts.ru/Inputs/AmigaMouseJoy_pinout.shtml
[2] http://pinouts.ru/Game/genesiscontroller_pinout.shtml

30 August 2013, 12:13	#8
Jope - Join Date: Jul 2003 Location: Helsinki / Finland Age: 43 Posts: 9,863	There has been a lot of discussion about using Sega Megadrive/Genesis pads on the Amiga. It seems the Paula pin servicing the controller port pin 5 can handle the current drawn from it, since it's designed to handle being shorted to ground by a middle mousebutton. Unmodified pads shouldn't burn anything in the Amiga. One reason to do the modification is, that the Amiga cannot control the multiplexer inside an unmodified Megadrive pad, thus you will only be able to use two of the fire buttons. Pin 7 low = A+Start are readable, Pin 7 high (locked to this state in an unmodified pad) = B+C are readable. Don't connect them to a C-64 without doing the 5<->7 swap. The circuit is different in those. The following is recorded here for history's sake, make of it what you will. Many people have noticed that they seem to work just fine unmodified and have no second thoughts about it. However you should be aware that there are a few things to understand and after that you can make the decision whether to keep on using the unmodified pad, or to do something about it. The difference is that on atari sticks the +5V supply[1] is on pin 7, and on the megadrive, pin 7 is a signal pin instead[2]. So why you shouldn't just plug in a megadrive pad into an Amiga unmodified? If the POTGO register has been configured to set pin 5 of the joystick port as an output with the value 1, you are driving the megadrive pad's power supply from a signal pin and you might fry the signal driver in your Paula. To be safe, you should either make an adapter that passes all other pins through but crosses 5 and 7, or modify the megadrive pad itself, by desoldering these two wires from the circuit board and reconnecting them in each other's place. This goes the other way if you have a USB -> Megadrive pad adapter and connect an Atari joystick to it, you're driving the Joystick's autofire circuit's Vcc with the megadrive adapter's pad duplex select signal instead of an actual power supply line (which would be on pin 5 for the megadrive). Sure, it might work forever if you're lucky, but then again it might burn out the driver for that signal at the controller chip inside the USB adapter if you're unlucky. Then you can't use megadrive pads with the adapter any more. [1] http://old.pinouts.ru/Inputs/AmigaMouseJoy_pinout.shtml [2] http://pinouts.ru/Game/genesiscontroller_pinout.shtml Last edited by Jope; 30 January 2019 at 08:37.