JTAG implementation

Hello everybody. I'm interested in developing a JTAG system using a FPGA 
programmed in VHDL. Is there some good source on line that can help me 
in doing that? Where can I found the specification of JTAG standard? Are 
they free available?

Giovanni wrote:
> Hello everybody. I'm interested in developing a JTAG system using a FPGA 
> programmed in VHDL. Is there some good source on line that can help me 
> in doing that? Where can I found the specification of JTAG standard? Are 
> they free available?

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