clk=0: ena=0, enb=0, wea=0, web=0 --> out=0
clk=1: ena=0, enb=0, wea=0, web=0 --> out=0
clk=0: ena=1, enb=1, wea=0, web=0 --> out=0
clk=1: ena=1, enb=1, wea=0, web=0 --> out=0
clk=0: ena=1, enb=1, wea=1, web=1 --> out=0
clk=1: ena=1, enb=1, wea=1, web=1 --> out=1
clk=0: ena=1, enb=1, wea=1, web=1 --> out=1