PS/2 keyboard and connector notes for Development board

[Xiphod]

The "manual" should have a reminder that PS/2 connectors are not "hot swappable."

I went ahead and risked trying it - that's what the Development board is for, right? The first time, the "new" PS/2 keyboard didn't respond - I had to reset the system, but there was no overall adverse effect. On the 2nd time, testing a different keyboard, the system shutdown (powered off) when I reattached the new PS/2 kbd. But I think the actual reason is because I bumped the ATX power connector in the process.

So that's enough "testing" of that for me on that. I recall that being the case back in the day (early/mid 90s) that you couldn't add or swap in a new PS/2 device after power up of the system (mice or keyboard). And it's not worth the electrical risk to the system.


Also, I wasn't sure, but: would a full 350W ATX power supply work? Sorry to ask, I'm sure it's been discussed before. I used the 12V adapter to the "ATX slot" that was provided, but I wasn't sure if a "full sized" ATX power supply could also be used (obviously overkill, but if it's all you had? Any 250W to 1000W ATX?)


And as a very positive note: so far every PS/2 keyboard I've tried has worked with the Commander X16, I have about 10 of them. That was NOT the case for the ArgonLite - that's why I ended up with so many PS/2 keyboards, I kept trying so many to finally find one that did work with the Argon, and the 10th one finally did.

[Stefan]

I know some work was done previously to enable hot swapping.

I never tested it though, as I’m afraid to damage the board.

It’s also possible that R43 changes to the SMC ”disabled” hot swapping by mistake.

Great that we got the PS/2 comm stable as such. I have only tested one keyboard, and that worked.

[Wavicle]

I recommend putting hardware-specific questions in the hardware support forum. I know the forums here aren't exactly hopping with activity, but I'm more likely to scan the hardware forum.

PS/2 hot swap does work, as much as PS/2 hot swap can, but your keyboard needs to participate well in this process along with the X16 since the PS/2 spec does not cover hot swapping.

I just flashed the official R43 release onto my SMC, verified all fuses, unplugged the keyboard, powered the board on, and plugged the keyboard back in. It worked as expected. This was with the official keyboard (Perixx Periboard-409).

[TomXP411]

Hot swapping PS/2 is definitely not recommended. I actually did burn out a keyboard controller on a PC once by hot swapping a keyboard. I had to replace the motherboard on that PC.

The PS/2 standard has never been hot swappable; this includes the AT and XT keyboard interfaces. Plugging in a keyboard while the computer is on can wreck the keyboard controller chip. Don't do it on any computer with a PS/2 or DIN keyboard connector.

[DragWx]

Out of curiosity, what causes the damage when these connectors are hot swapped? I remember the C64 joysticks were supposedly not hot swappable either, but I never understood why exactly.

[TomXP411]

Out of curiosity, what causes the damage when these connectors are hot swapped? I remember the C64 joysticks were supposedly not hot swappable either, but I never understood why exactly.

C64 joysticks can be hot plugged just fine: there's no current draw when the joystick is not being used. In other words, whoever told you this doesn't understand electronics - because there are no electronics in a typical Atari style joystick - just switches.

When you have a multi-conductor partly plugged in, you run the risk of the positive terminal being hooked up, with the ground disconnected. The ground is used for a lot of things, but its most important job is to have a stable place to sink current. With the ground not connected, current goes places it shouldn't. At best you get malfunctioning ICs and at worst, you get sparks and overvoltage, and you burn things out.

Connectors made to hot swap will usually have different size leads, with the power pins being a different length than the data pins. This gives the device a chance to safely ground itself before powering up. USB goes a step further, and the power is actively managed, with the host and device working together to manage power delivery.

[DragWx]

Ahh, I see now, thanks for explaining it.

So it really would come down to the standard to take hot plugging into consideration, but I wonder if there's some hypothetical way to facilitate it in the existing ps/2 ports anyway. Just for fun, anyway, I'm not sure how important hot swapping the keyboard and mouse actually is.

[Daedalus]

I think the short answer is no, and it's about the connector. A basic need for "hot swapping" is to be assured that ground connects first, and as far as I know, the connector the PS/2 uses is a generic type not meant for that.

Sure, there's nothing stopping someone from building a special connector, and I wouldn't be surprised if they exist, but unless it was that way from the get go like the USB connectors, it seems dubious.

Sorry, didn't see where Tom beat me to that.