I would do something to prevent the two from both trying to talk on the
serial line at once.  Like, say, a 74 series logic multiplexer.  The 74158
should do it.  Unless the emulator needs to communicate, it can let the
keyboard have the bus.  If it wants the bus, and the keyboard isn't
using it, it can take control.  I forget how many data lines are needed
for PS/2 (I'm making the assumption that this is PS/2 based), but the
74158 has 4 2-input multiplexers in it.

This may not be the optimal solution, but I think it's the quickest and
maybe the simplest.  At $0.45 each from Digikey, it's also probably the
cheapest.

Mike H.

>I want to connect a pc keyboard emulator (based on 16F84) along with a pc
>keyboard. do I need to do any special circuit for it or both can work
>simultaneously?

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