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I though SMS controllers were OK?


eightbit

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You know, I could swear I have used SMS (Sega Master System) controllers on Commodore machines in the past with no issue. But today I had an issue.

 

I wanted to test the directionals of one SMS pad I have and usually I use a joystick tester application I have for the C64/C128. I was using a C128 today to do this. Plugged the controller in port 2, ran the test, all seemed good. I did press the second button on the SMS pad and of course it did nothing as only button 1 registers as fire on the Commodore.

 

After I was done with the test I turned off the C128, unplugged the SMS pad and returned my Hyperkin joystick. When I turned the C128 back on the fire button on the controller would not work! Directionals worked, but not the fire button.

 

I suspected a CIA issue and I was right. After swapping around the CIA's the fire button on port 2 works. So, one slightly defective CIA it appears.

 

Do you guys think the SMS pad did this? Maybe when I pressed button 2? Or just an odd coincidence?

 

Either way, now I have to source another CIA....and I am never introducing a SMS controller to the computer ever again!

Edited by eightbit
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Just now, bluejay said:

 I've heard stuff about Sega controllers causing issues on Commodore machines quite a few times. Stuff like frying CIAs and various odd unhealthy behavior. So most likely it's your SMS controller at fault.

 

For years I have heard this for Genesis controllers, but never SMS controllers as they are wired differently. Many people on Lemon64 swear by using the SMS pad as well. But, I have to agree. I won't test it again that is for sure!

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From what I understand, pressing button 2 would tie POTX (in the SID chip) to ground. In itself that should not make any change to the CIA unless there occurs some reverse current or whatever. In comparison, the Genesis pads tie its Select to 5V to enable buttons B and C, which translated to C64 means tieing 5V to POTY (again in the SID chip). This is what the C64GS did to get additional buttons, but it recommended to put a ~300 ohm resistor between the two, to reduce the voltage which of course a Genesis controller doesn't have. Once or twice it might not damage the SID chip but multiple and long lasting presses on buttons B and C cause damage when feeding 5V directly into the SID chip.

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1 hour ago, eightbit said:

I just checked the SID chip to be safe and it is fine. I spoke to Ray Carlsen about what happened and he thinks it may have just been an odd coincidence and the chip was just failing. Really weird timing if that is the case.

I would more readily accept this hypothesis.  The CIAs can be fragile devices but still work fine until just one little thing changes.  I blew out a CIA once by swapping out a PLA.

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As near as I can tell, the issue with Sega Genesis/Mega Drive controllers is that they utilize pin 7 for the start button (and possibly two of the three other action buttons as well), which on Commodore ports is mapped to +5v which can be shorted into either the CIAs or the SID depending on the button pushed.  However, Master System controllers don't utilize pin 7 at all.  The D pad and Button 1 are mapped the same as an Atari stick.  Button two is wired to pin 9, which on Commodores grounds the pot pin used for paddle/mouse inputs on the SID.  To my knowledge, this is safe (or at least, I've never had a problem with it).

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1 hour ago, carlsson said:

What if the cable somehow has a short, and you effectively tied one CIA input to the SID POTX in some sort of short circuit? OTOH if the cable has a short, that would happen when you pushed the first button as well.

Looking over the pinout for these, if a short did exist between both action buttons, then that connection would be present whether the buttons were pushed or not.  Instead, pushing button 1 or 2 would ground both the SID and CIA simutaneously.  Assuming that the short between the SID and CIA didn't cause an immediate malfunction for the computer, then such a short would likely mean that pushing button 2 would result in the same action as pushing button 1 (fire/jump/whatever action the game dictates).  

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3 hours ago, DistantStar001 said:

Looking over the pinout for these, if a short did exist between both action buttons, then that connection would be present whether the buttons were pushed or not.  Instead, pushing button 1 or 2 would ground both the SID and CIA simutaneously.  Assuming that the short between the SID and CIA didn't cause an immediate malfunction for the computer, then such a short would likely mean that pushing button 2 would result in the same action as pushing button 1 (fire/jump/whatever action the game dictates).  

If the cable had such a short wouldn't it affect its functionality on a Sega Master System as well? I tested both controllers I have on a real Sega Master System using a game (Fantasy Zone) that uses both buttons. UP/DOWN/LEFT/RIGHT (and diagonals) work fine in the game and button 1 (shoot) and button 2 (bombs) work fine as well.

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21 minutes ago, eightbit said:

If the cable had such a short wouldn't it affect its functionality on a Sega Master System as well? I tested both controllers I have on a real Sega Master System using a game (Fantasy Zone) that uses both buttons. UP/DOWN/LEFT/RIGHT (and diagonals) work fine in the game and button 1 (shoot) and button 2 (bombs) work fine as well.

Yes.  If such a short were present, then pressing either button would ground both at the same time (shoot and bomb at once).

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  • 4 months later...
  • 2 weeks later...
On 12/10/2020 at 10:23 AM, carlsson said:

From what I understand, pressing button 2 would tie POTX (in the SID chip) to ground. In itself that should not make any change to the CIA unless there occurs some reverse current or whatever. In comparison, the Genesis pads tie its Select to 5V to enable buttons B and C, which translated to C64 means tieing 5V to POTY (again in the SID chip). This is what the C64GS did to get additional buttons, but it recommended to put a ~300 ohm resistor between the two, to reduce the voltage which of course a Genesis controller doesn't have. Once or twice it might not damage the SID chip but multiple and long lasting presses on buttons B and C cause damage when feeding 5V directly into the SID chip.

The simpler way it was explained to me, was that if you pressed "B" and hit a keyboard key at same time, it would fry the chip.

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