There are lots of free resources on the Internet to learn. Here I list several legally free VHDL books. Some of the sites require registration to download the free book.

FPGA prototyping book – https://fpgasite.wordpress.com/2016/06/23/prototypical-fpga-prototyping-free-book/

Altera’s FPGA for Dummies – https://fpgasite.wordpress.com/2016/03/25/fpga-for-dummies-free-book/

MicroZed Chronicles (Vol. I) – https://fpgasite.wordpress.com/2016/08/13/the-microzed-chronicles-free-fpga-book/

Free Range VHDL – https://fpgasite.wordpress.com/2016/07/24/free-range-vhdl-free-book/

Xilinx’s High Speed Serial IO – https://fpgasite.wordpress.com/2016/04/07/high-speed-serial-io-book/

FPGA’s now what – https://fpgasite.wordpress.com/2016/04/14/fpgas-now-what-free-book/

The Zynq book – https://fpgasite.wordpress.com/2016/06/28/the-zynq-book-free/

Introducing Spartan 3E and VHDL – https://fpgasite.wordpress.com/2016/07/09/introducing-the-spartan-3e-fpga-and-vhdl-free-book/

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