1 Explicit event
The value changes on nets and variable can be used as events to trigger the execution of a statement.
The event can also be based on the direction of the change that is, towards the value 1 ( posedge) or towards the value 0 (negedge).
- A negedge shall be detected on the transition from 1 to x, z, or 0, and from x or z to 0
- A posedge shall be detected on the transition from 0 to x, z, or 1, and from x or z to 1
@(trig or enable) rega = regb; // event "or" is the same as ","
@(trig, enable) rega = regb;
@(posedge clk_a or posedge ck_b or trig) rega = regb;
always @(a, b, c, d, e)
always @(posedge clk, negedge rstn)
always @(a or b, c, d or e)
2 Implicit event
// Example 1 always @(*) // equivalent to @(a or b or c or d or f) y = (a & b) | (c & d) | myfunction(f); // Example 2 always @* begin // equivalent to @(a or b or c or d or tmp1 or tmp2) tmp1 = a & b; tmp2 = c & d; y = tmp1 | tmp2; end // Example 3 always @* begin // equivalent to @(b) @(i) kid = b; // i is not added to @* end // Example 4 always @* begin // equivalent to @(a, b, c, d) x = a ^ b; @* x = c ^ d; end
原文：http://www.cnblogs.com/mengdie/p/4684144.html