The rule when attaching a signal name

As for 2 to 8 pins of U1 and U2, each pin is connected by the network name of D0 to D7.

Since "1" pin of U1 and "1" of U2 connect with the wire, they are connected in one network.

19 pins of U1 and U2 are connected to GND.

As for "1" pin of U3, and "1" of U4, a signal name is connected as a network of "SEL0."

Although "10" of U1, U2, U3, and U4 is not displayed, a non-displaying power-supply pin is connected to the network of GND.

"20" pins are similarly connected to the network of VCC.

Since it does not connect at a junction, 11 pins of U4 are not connected to network name CLOCK.

Although the bus of 18 to 11 pins of U1 and 3 to 18 pins of U3, 18 to 11 pins of U2, and 3 to 18 pins of U4 have separated by bus Since a signal name is the same, it connects with a network. (In DA0, "18 of U1", "18 of U2", "3 of U3", and "3 of U4" become the same network.)