Rule 90 is a one-dimensional cellular automaton with interesting properties.
The rules are simple. There is a one-dimensional array of cells (on or off). At each time step, the next state of each cell is the XOR of the cell's two current neighbours. A more verbose way of expressing this rule is the following table, where a cell's next state is a function of itself and its two neighbours:
|Left||Center||Right||Center's next state|
(The name "Rule 90" comes from reading the "next state" column: 01011010 is decimal 90.)
In this circuit, create a 512-cell system (q[511:0]), and advance by one time step each clock cycle. The load input indicates the state of the system should be loaded with data[511:0]. Assume the boundaries (q[-1] and q) are both zero (off).
module top_module( input clk, input load, input [511:0] data, output [511:0] q );
1 10 101 1000 10100 100010 1010101 10000000
This forms half of a Sierpiński triangle.
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