Sir,
I am an experienced electronics engineer in a leading electronics company.
I developed so many Embedded boards, FPGA boards, SoC boards, Microcontroller boards using ORCAD Cadence and written codes in C, VHDL, Vivado.
I will design a 256 input Priority encoder in a readily available Xylinx ZYNQ board.
You can simply dump my code in your ZYNQ board and it can start working as 256 input priority encoder for you.
Or if you want fresh schematic using ORCAD cadence, then also it is possible.
Thanks