Absolute Shaft Encoders also known as Absolute Rotary Encoders provide a unique binary bit output for each resolvable position. This unique bit pattern (shaft position) is read directly from the disc arrangement within the encoder, so that if power is lost, the true shaft position value is not lost. On power up, the true actual shaft position value is read again from the encoder disc, so the machine can continue its operation without the need for returning to a home position before continuing. Absolute encoders are available over one single turn, or many thousands of turns, known as Multi-turn Absolute Encoders. Available output codes include Gray, Gray-Excess, Binary and BCD, and various serial, SSI & bus system encoders are also available for interfacing to various types of PLC such as Profibus DP, CAN bus, Interbus and several others.