The use of shift registers as input/output expansion allows the selection of lower pin count, and thus, lower-cost microcontrollers. They can reduce the total number of controllers required. A further advantage of the 74HC595 is that it also includes a serial output. This feature allows several devices to be cascaded together. Now the same three microcontroller pins that were controlling eight LEDs can be used to control 16 or 24 LEDs. In some cases, the 74HC595 can be used to drive LEDs directly. For applications that drive the LEDs with voltages higher than 6.0 V or ground current that exceeds 70 mA, external drivers are required.