Conceptual Question On Separate Ps/vs Files

Hi all,
During my journey to go away from effects11 to own shader management, there's something I don't understand.

Effect files/FX:
- contains vertex and pixel shader (functions)
- contains constant buffers which can be used by the VS, PS (and GS etc)
- contains techniques which pick variants of combinations between the shaders

Now from what I understood, I will create separate files for my vertex and pixel shaders. So far so good.

But what do I do with constant buffers that are used by both the PS and VS (for example a CB per frame)?

- do I include the exact same CB definition in both the VS file and PS file?
- is 1 enough? And will the HLSL compiler accept that the CB is not defined in the shader file?
- do I need to create separate CB's for the PS and VS? I hope not, because the counter that goes to 14 will raise quickest that way.
- .... Other/ better option?

Any input is appreciated.
Note; I'm using VS 2013 community as IDE, which can compile all shaders for me using FXC under the hood.