I want to use a USB keyboard and mouse with an old server. Not very old but the USB ports are taken up. I plan on using an active USB to PS2 convertor (Tripp Lite brand)

But I need to be able to switch the keyboard out during operations. So my question is, would the USB to PS/2 converter eliminate the possibility of PS/2 port damage?

  • What kind of physical damage are you worried about? Pins bent or something electrical? Because electrical is not really physical. – Giacomo1968 May 30 '18 at 1:15

If you're using a PS/2 port that's on your computer, and you remove something from that PS/2 port and plug something else in, you are risking damage to one of the bridge chips on the motherboard (the one that includes the PS/2 interface).

(In traditional PC motherboards this would be the "south bridge" chip. In more modern setups where the north bridge functionality is incorporated into the CPU, it's the "platform controller hub" for Intel, or "Fusion Controller Hub" for AMD. Or in very small platforms it would be in the SOC, "System On a Chip".)

If you unplug the USB keyboard that's going into your converter and plug in a different one, you should be fine.

The problem with hot-plugging and PS/2 is not in the keyboard or mouse but in the PS/2 connector itself. In a connector designed for hot plugging, the contact lengths are staggered so that ground connects first, then power, then the data circuits, and vice versa when unplugging. The PS/2 interface uses a standard mini-DIN connector that was not designed that way. So when you plug in a PS/2 anything, there's a very good chance that the data pins connect before power does, and the result is that the keyboard attempts to draw power through the data interfaces. The line drivers and receivers are just not designed to handle that much current, and they just go poof.

But with an active USB device to PS/2 port adapter you should not have that problem from hot-swapping USB things plugged into the adapter.

On the other hand, what the server will be seeing is the disconnection and connection of a PS/2 keyboard. This won't damage anything but it may not properly detect and initialize the new keyboard. A reboot should cure it.

I have to ask: Why not just use a USB hub?

  • Thanks for this answer. Now I just need to know if linux will auto recognize my keyboard after hotswapping without rebooting – Blake King May 30 '18 at 2:35
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    All this is motivated by your server's shortage of USB ports. Why not just use a USB hub? They are cheap, small, and reliable. – Jamie Hanrahan May 30 '18 at 5:07

Both USB and PS/2 have grounding and therefor the active USB converter plugged into the PS/2 port would provide safe hot swapable USBs so long as the PS/2 ports are not hot swapped.

In any case relatively new hardware (circa 2005) most probably also have more robust I/O protections and while technically are not hot swappable are fairly well protected from damage.

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