System power control using a power supply to provide voltage to subsystems in which a subsystem determines its operating state based on the voltage received by the subsystem

An electrically powered digital system having a plurality of electrical power consumption states including an active state and at least one power saving state, the system comprising a plurality of subsystems each having a plurality of subsystem power states including an active state and at least one power saving state, the electrical power consumption states of the system corresponding to respective different configurations of subsystem power states of the subsystems, a power supply unit for supplying power to the subsystems, wherein a subsystem has first and second power saving states, wherein the first power saving state provides no active functions from the subsystem and reduces latency to return to the active state compared with the second power saving state and when the subsystem is the first power saving state, the power supply unit provides a non-zero voltage to the subsystem that is less than a voltage supplied to the subsystem when the subsystem is in the active state and wherein the non-zero voltage is detected by the subsystem and used to determine the state of a subsystem and both increases and decreases in non-zero voltage levels detected by a subsystem induce state changes in the subsystem.

A printer having an active state and a plurality of power saving states, the printer comprising:

• a plurality of subsystems each having an active state and at least one power saving state, the power requirements of the subsystems being dependent on the state of each of the subsystems and the printer states corresponding to respective different configurations of subsystem states;
• a power supply unit for supplying power to the subsystems, wherein the power supply unit supplies a non-zero voltage to a subsystem in a power saving state, the non-zero voltage being less than a voltage supplied during the subsystem active state wherein a voltage is
• supplied to each of the subsystems by the power supply unit dependent on which of the plurality of power saving states of the printer is required, and a non-zero voltage less than a maximum voltage received by the subsystem is used by the subsystem to set the state of the subsystem.