Blocking and Non-Blocking Assignments

always @(posedge CLK) begin temp = B; B = A; A = temp; end

always @(posedge CLK) begin A <= B; B <= A; end

• Blocking assignments (Q = A)

  • variable is assigned immediately before continuing to next statement
  • new variable value is used by subsequent statements

• Non-blocking assignments (Q <= A)

  • variable is assigned only after all statements already scheduledare executed
    • value to be assigned is computed here but saved for later
  • usual use: register assignment
    • registers simultaneously take their new valuesafter the clock tick

• Example: swap

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