Hardware Description Language

A HDL definition defines the internal wiring of a chip and consists of 2 parts

A header section - defining the interface of the chip
A parts section - defining the names and internal top

Tip

Each chip is defined in a seperate text file
A chip called Xxx is defined in a file called Xxx.hdl (case sensitive!!)
Keywords are capitalised
Identifier name may be sequence of letters and digits not starting with a digit
Whitespace has no meaning
Lines end with semicolons

Defining a Chip

CHIP Xor {
   IN a, b;
   OUT out;

   PARTS:
   And (a=a, b=b, out=x);
   Or (a=a, b=b, out=y);
   Not (in=x, out=notx);
   And (a=y, b=notx, out=out);
}

These parts are like functions but each paramater is defined when calling it

The order of the parts is not important
So a Xor gate takes 4 ‘functions’ to work

Defining a Chip (Buses)

Buses are a collection of pins
Buses can be used as input, output or internal pins
Buses are indexed (similar to arrays in C)

CHIP foo {
   IN in[8];
   OUT out[8];

   //Parts
}