[coasttech]

Is this for real??

“Whether you use a DIN or mini-DIN connector, remember that the keyboard receives power from the system board, so you should never unplug or plug in a keyboard while the computer is powered on. Doing so could short out the keyboard connector, requiring you to replace the entire system board.”

Thanks!

[Advertisements]

Yep thats absolutely true. Where do you reckon keyboards get their power from to light the CAPS / NUM / SCROLL LOCK LEDs up if its not from the keyboard port?

[Samm]

Yep thats absolutely true. Where do you reckon keyboards get their power from to light the CAPS / NUM / SCROLL LOCK LEDs up if its not from the keyboard port?

[coasttech]

I have to say I am guilty of do this many times. But I just can’t see how this could fry you MoBo!

[Samm]

Because you are connecting a metal plug into a live socket (keyboard port). The chances of doing any damage are fairly slim but electronic components are very sensitive so it's not advisable. You really should only connect/disconnect it when the system is powered off.

[coasttech]

Does this only apply to only the PS/2 ports… or all the different ports (Parallel, Serial)? I know with USB you can plug that in and out with no problem. What is different with that? Is it not still a live feed of electricity?


and PM Blair is the bomb!!! ....jk

Edited by coasttech, 21 March 2006 - 08:55 PM.

[Samm]

Does this only apply to only the PS/2 ports… or all the different ports (Parallel, Serial)? I know with USB you can plug that in and out with no problem. What is different with that? Is it not still a live feed of electricity?
and PM Blair is the bomb!!! ....jk

This is a complicated one but if you really want to know, I'll tell you.....

Technically, serial (RS232) & parallel ports are not powered.

However, there are some parallel/serial devices which need power but do not come with their own power source. Serial mice, for example, need a small amount of power for the circuitry thats inside them. Also, dongles require a small amount of power but they do not have batteries or external power packs either. Serial Mice etc draw their power from the port by using the output signal (data) lines in the port. As serial ports were originally intended for communication between 2 devices (e.g between 2 computers), there are 3 output signal lines in a serial port (TD, RTS & DTS). Signals sent from the port represent 1/0 or ON/OFF (think of binary). This form of signal is represented by voltages, e.g zero or negative voltage = OFF, 3V & above = ON.

Devices such as serial mice are able to use these signal line to acquire the power they need to drive their own circuitry. Obviously devices which need more power than this (eg printers), must have their own power source instead of taking power from the port.

USB ports are metal & are powered and USB devices may be plugged in & out of live ports (hot swappable), as you said. The reason this is safe is due to the design of the USB connectors themselves. They are designed with the outer metal sheath to be more prominent than the internal connectors. This means that the outer sheath always make contact with the port first. As this outer sheath provides the 'ground' connection, this means that the resulting circuit is already grounded (or earthed) when the live parts come in contact. This eliminates the risk of static electricity damaging any components on the board or in the USB device.

[coasttech]

WOW! I wish you where my teacher!! Very well explained, and I understand now thanks!

Also because such a device as a Serial Mouse draws power from the Serial Port, does the same rule apply as it does for the Mini-Din.

And also if the power (lets say for a Printer) is coming from the Printer it self.. if the Printer was powered on and then plugged into the Parallel Port.. is there not a potential for there to be a shock coming from the Printer to the Computer?

[Samm]

PS/2 (mini-din) mice also require power from the PS/2 port obviously but they get the power in a slightly different way. Serial mice are designed to use the voltages carried on the signal lines of the RS232 port (as explained before). In other words, this method is a work-around to overcome the fact that serial ports do not provide an actual line designed for powering serial devices. PS2 ports however do provide power which is meant for powering PS/2 devices. Therefore, ps/2 devices (mice & keyboards) do not need to acquire power from any signal lines, as they are already supplied with the necessary power from the 5V output line of the PS2 port.

Re. your question about parallel devices being connected whilst powered on - in short the answer is no. Remember that like serial ports, parallel ports are not actually powered (i.e they don't have an output power line), nor do they receive power from the parallel device. Like mice, the only way a parallel device can draw power from the port is if it has been designed to do so by using the signal lines. As printers have their own external power source, they are therefore not designed to do this.

In fact the only parallel devices that I can think of that are designed to extract power from the port in this way, are dongles. And these must be connected only when the system is powered off, otherwise you would risk damaging something as you suggested.

[coasttech]

You rock!

[Samm]

Thank you.