PLD software intro
PLD design software
When PLDs such as PALs had only a thousand or fewer programmable connections, it was possible to do the design by hand. A chart provided by the manufacturer was used to mark in the desired connections and then the fuse numbers were set up in the programmer using data editing commands. Since the 80's and 90's design software has become the only way, because device sizes just got too big to keep track of the details. Devices are now approaching a billion transistors, with millions of programmable connections. The use of software involves coding the design in a Hardware Decription Language (a HDL). Using a HDL brings all the benefits of abstraction, macros and modules into the development cycle.
The following expandible sections show a little bit about the major Hardware Design Languages that are specific to, or used to design for PLDs (roughly in chronological order). In each case I code the same simple example function (a "D" flip-flop with an AND term feeding its D input), as in the image to the left:
Not entered is STAPL. I just haven't had any exposure to it. If anybody wants to add an
equivalent paragraph or two about it, notify me via the contacts page 
and I'll give full credit!