Digital Circuits specification in VHDL

The VHDL "manual"  advised for the course is the XST User Guide chapters "HDL Coding techniques' and 'VHDL Language Support', available from Xilinx: Documentation UG627
The book "Hardware Design Using VHDL RTL" Pong P. Chu, 2007 contains a significant number of examples of VHDL components specification for synthesis. Most of these examples are available in http://academic.csuohio.edu/chu_p/rtl/index.html

The book "Synthesis of Arithmetic Circuits: FPGAs, ASICs and Embedded Systems," Deschamps, Bioul and Sutter, 2006 contains some examples of VHDL specification of basic arithmetic circuits in http://www.arithmetic-circuits.org/arithmetic/vhdl_codes.htm

An on-line description of all of VHDL elements can be found in Compact Summary of VHDL or on the VHDL reference material page.