Interfacing PS/2

Hi all,

I have a project to make, a device that will send small amounts of data through PS/2 to PC.
It will put some data to application dialog, to a field with current focus.
Application is old, and not supported, so I have to stick with this technology. USB or serial or LAN just won't go.

I have seen solutions with PC keyboard connected to AVR, and this is easy.
Problem is, the keyboard should be still operational with my device connected.
PC should see the keyboard, and the device.
The user will be using them, advised not to use them simultaneously.

Should I disconnect data line between PC and keyboard to send data with my device ?
I have seen barcode readers, that do exactly the thing I want, but I don't have any to disasemble it and see what's inside.
I believe they have parallel connection with the keyboard, but I am not sure.

I don't know how the keyboard will react to unknown data on its data bus.

Do you have any experience with this matter ?
I would appreciate any solutions.

Regards
Pees

you can just disconnect the keyboard clock and data when your device wants to send something. You may wish to delay a short while before & after transmitting, in case there is a transfer occurring (e.g. disconnect kb, delay, transmit, delay, reconnect kb), of you could monitor the lines and make sure there is nothing happening before transmitting.