Encoder, servo motor, servo system, and encoder control method

An encoder comprising:

• an angular position information detector configured to detect angular position information indicating an angular position of a rotating disk within one rotation thereof;
• a multi-rotation information detector configured to detect multi-rotation information indicating a number of rotations of the disk;
• a battery configured to supply a power to the multi-rotation information detector when an external power is not supplied to the encoder;
• and
• a single processor,
• wherein the single processor executes a process of switching between supply of the power from the battery to the multi-rotation information detector and stop of the supply, and a process of performing a predetermined arithmetic process based on the multi-rotation information detected by the multi-rotation information detector,
• the power is supplied through the processor from the battery to the multi-rotation information detector to detect the multi-rotation information, when the external power is not supplied, and
• the processor stops the supply of the power from the battery to the multi-rotation information detector, after acquiring the multi-rotation information from the multi-rotation information detector.