Abstract: A subprocessor is used to interface between subsystems and to reduce the amount of dedicated hardware used to implement the subsystems in a hand-held computer. The subprocessor includes basic processing system resources such as random-access memory (RAM), read-only memory (ROM), a processor, input/output (I/O) facilities, etc. Selected functions in subsystems are achieved by firmware instructions executed by the subprocessor as opposed to a main processor that is also used in the computer. This approach can provide efficiencies such as low power consumption, less required space, less routing overhead, easier transfer of inter-subsystem information, and other advantages.

Abstract: A bi-directional DC-to-DC power converter is provided. The power converter has three modes of operation: (1) a step-down mode, in which the power converter converts power in a first direction (such as from a high-voltage power bus to a low-voltage power bus), and (2) a step-up mode, in which the power converter converts power in the opposite direction (such as from the low-voltage power bus to the high-voltage power bus), and (3) an off mode, in which no power is transferred. A single power converter may therefore be used to replace both a conventional step-down converter and a conventional step-up converter. The power converter may provide a battery charge-control functionality, and may be used to charge a battery that may, for example, provide a source of power to a component of an electrical device.