Megadrive pad for Atari ST

[Alc]

Hi all.

I want to use a Megadrive pad on my Atari ST. From what I've read, their joysticks/pads are functionally very close, as the Megadrive apparently supports Atari 2600 pads, and some people say that their 3-button Megadrive pads just work on their Atari ST. I've tried all mine, and they don't, so I'm left wondering where to go. I've found a crap third-party SMS pad which works, and it's ok for the moment, but ideally I'd like to use a first-party Sega pad. Not fussed whether it's a 3-button or a 6-button, happy to get the soldering iron out and do whatever's necessary, although if I could retain compatibility with both that'd be a bonus.

So far I've tested the following:

Megadrive 6-button pads: fire works, d-pad doesn't.
Megadrive 3-button pads: same
Third-party Megadrive pads: same
Master System pad (first-party): d-pad works, neither buttons do anything.

All hardware is from a PAL territory (UK).

Apparently the pinout for a standard Atari pad is as follows:
Pin Color    Function
1  White    Up
2  Blue     Down
3  Green    Left
4  Brown    Right
5           no contact
6  Orange   Fire button
7  Red      +5V, max. 50 mA
8  Black    Ground
9           no contact
Only one fire button, but other buttons have been added along the way for other Atari consoles/computers (and other platforms), presumably to lines 5 and 9.

I've also read a document linked in another thread here which mentions some kind of "compatibility mode" that the Megadrive has for other joysticks, and a lot of signal processing stuff which is over my head, really. Is there any simple modification of a Megadrive pad that will enable it to work with the Atari without having to sacrifice compatibility with the Megadrive, or do I need to rewire the Megadrive pad up like an Atari one?

[NFG]

I used to use a Master System pad on my ST with no trouble.  While I can't remember using a MD pad, it SHOULD work.  Have you tried any other pads on your ST, that work fully?  Have you tried these pads on a MD to make sure they work?

MD 6-button pads have a compatibility mode, but it's controlled by the SOFTWARE not the hardware.

Basically, unless your hardware (the ST or MD) is sending a signal on the MD's clock/select line the pad should be stuck in regular 2-button pad mode: UDLR, ST and B.  The ST should understand UDLR and B with no trouble.

[Alc]

I used to use a Master System pad on my ST with no trouble.  While I can't remember using a MD pad, it SHOULD work.  Have you tried any other pads on your ST, that work fully?  Have you tried these pads on a MD to make sure they work?

My third-party SMS pad works fine, but I've tried eight Megadrive pads, and none of them work. I've never had any functional issues with any of them, outside of the odd dodgy d-pad (i.e. not circuitry). Obviously it's not feasible that they're all knackered, so I'm guessing something is screwy with the Atari STe, or my one at least.

MD 6-button pads have a compatibility mode, but it's controlled by the SOFTWARE not the hardware.

Basically, unless your hardware (the ST or MD) is sending a signal on the MD's clock/select line the pad should be stuck in regular 2-button pad mode: UDLR, ST and B.  The ST should understand UDLR and B with no trouble.

So, if I add a switch to the select line, the pad should have to default to the correct connections, right? I'll test by just lifting the contact first, or should I attach it to ground?

Thanks for the quick reply, by the way.

[NFG]

If you tie the select line (pin 1) to GROUND you'll get the A inputs, which are basically useless (most of them are just tied to ground instead of an input button).



   Pin 1 - Select   Pin 16 - Vcc (+5V)
   Pin 2 - 1A   Pin 15 - ENABLE (Ground)
   Pin 3 - 1B   Pin 14 - 4A
   Pin 4 - 1Y   Pin 13 - 4B
   Pin 5 - 2A   Pin 12 - 4Y
   Pin 6 - 2B   Pin 11 - 3A
   Pin 7 - 2Y   Pin 10 - 3B
   Pin 8 - Gnd   Pin 9  - 3Y

I'm not sure if you can just lift the select pin or if you'll have to wire +5v to it, but in theory if you do that it should be just fine.

There's no encoder or other componentry in the MS pad so I cannot imagine any circumstance that would keep it from working...