Author Topic: KVM Switches  (Read 7495 times)

bitsandbytes

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KVM Switches
« on: January 06, 2012, 11:49:23 am »
Hi All,

Could someone please point me to an application note or reference design
dealing with KVM switches, I have searched on the net with no real  success.  I am interested in finding out how a KVM handles the  keyboard, mice and monitor signals for the computers that are not actively connected to the physical keyboard, mouse or monitor and also how they handle these devices on boot up.  I need to know both for USB type devices and PS2 type.  What I mean by physically connected is that the signals are routed form the devices to that computer, the other computers must be given some keep-alive signal for each of these devices.  I assume that all the devices are logically connected, not
physically, but I may be wrong.

Thanks
b&B

Jan Axelson

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Re: KVM Switches
« Reply #1 on: January 06, 2012, 12:39:23 pm »

bitsandbytes

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Re: KVM Switches
« Reply #2 on: January 06, 2012, 06:16:14 pm »
Hi Jan,

The link helps, but it does not go deep enough to the signal level to describe how to "fool" a computer into thinking that a device is attached.  I did some testing and it seems that the KVM that I have which is a USB KVM, enumerates as a hub, and shows three devices attached to it: a device with two interfaces (I assume the KVM box itself), a keyboard and a mouse.  I assume that when the KVM is pointing to another computer, the "hub" Nak's on the USB bus for the keyboard, mouse and KVM box.  I do not know how or what is needed for PS2, and further I have no idea of what is needed to fool the computer for VGA/DVI.

If you or someone else has a more detailed app note / reference it would be much appriciated.

b&B

Jan Axelson

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Re: KVM Switches
« Reply #3 on: January 06, 2012, 09:20:55 pm »
A USB hardware protocol analyzer would show the details of USB communications on any bus segment.

Jan