Xilinx CPLD design techniques online documentation

Xilinx has an online searchable database of information on programming their CPLD devices. It includes a number of cool tips and code samples for implementing bidirectional signals, clock dividers, global nets as well as information on CPLD attributes, the schematic library and controlling I/O pin voltages. In many cases code examples are provided in VHDL, Verilog, and ABEL along with schematic.