The Power Reduction Register (PRR), available in all picoPower devices, allows disabling of the clock to select peripherals while the core and other modules are running. The PRR is only usefull in Active or Idle mode. In other modes, the clock is already stopped. The traditional way of disabling peripherals is by I/O register bits, however peripheral control logic and the clock tree are still running. By using the PRR register, the AVR stops clocking individual peripherals, resulting in the selected peripheral being in power down sleep mode while the rest of the device is running and reducing overall power consumption. When stopping the clock to a peripheral, the current state of the peripheral is frozen and all I/O registers are inaccessible. When re-starting a module, it continues in the same state as before shutdown and a normal enable/disable will still leave some logic running. Also, resources engaged by the peripheral remain occupied when PRR is set. Therefore, the peripheral (e.g., the analog-to-digital converter and analog-to-digital multiplexer) should be disabled first.