The DM74LS503 register has an active LOW Enable (E) input that is used in cascading two or more packages for longer word lengths. A HIGH signal on E, after a START operation, forces Q7 HIGH and prevents the device from accepting serial data. With the E input of an DM74LS503 connected to the CC output of a preceding (more significant) device, the DM74LS503 will be inhibited until the preceding device is filled, causing its CC output to go LOW. This LOW signal then enables the DM74LS503 to accept the serial data on subsequent clocks.