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Line 1: − + − Now we lay down some actual code. First things first: comments! If you've ever done any programming, you know how wonderful comments are. If you've not done much coding, then remember that comments are not as pointless as they seem. Add descriptive comments or be murdered in your sleep 15 years from now by an irate engineer who has to decipher your legacy code. VHDL has no block comments, only line comments (the comment goes from the comment marker to the end of the line). The comment marker is a double dash with no spacing between them. Many development environments (for example Xilinx ISE) will auto-generate a large block of comments at the top of each file to be used to describe the file (who, what, where, when, why, how, and so on).+
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Now we're going to start laying down some actual code. This section develops the framework of a VHDL file and prepares your black box, which will be filled in by the next section.
== Some basics ==
== Some basics ==
First things first: comments! If you've ever done any programming, you know how wonderful comments are. If you've not done much coding, then remember that comments are not as pointless as they seem. Add descriptive comments or be murdered in your sleep 15 years from now by an irate engineer who has to decipher your legacy code. VHDL has no block comments, only line comments (the comment goes from the comment marker to the end of the line). The comment marker is a double dash with no spacing between them. Many development environments (for example Xilinx ISE) will auto-generate a large block of comments at the top of each file to be used to describe the file (who, what, where, when, why, how, and so on).
Secondly are the libraries. These are like the include statements in C/C++. Honestly I forget which libraries have exactly what tools in them, but a standard block will cover mostly any design you work on:
Secondly are the libraries. These are like the include statements in C/C++. Honestly I forget which libraries have exactly what tools in them, but a standard block will cover mostly any design you work on: