VHDL anyone ?

[Guido Piasenza <g.piasenza-at-ns.fidia.it>]

Hi folks,

does anybody know where I can find VHDL source
for a quadrature decoder ? 
Also, I have a doubt about encoders' voltage levels:
I think unipolar encoders are TTL compatible, so I
can input their values directly into a FPGA, whereas
I have no idea about how to interface bipolar
encoders.

Can anybody give me a hint ?

Thanks,
Guido