Absolute encoder output techniques！

    In commercial absolute encoders there are several techniques for transmission of absolute encoder data, including parallel binary, analog current, analog voltage, PWM,SSI, BiSS interface, ISI Profibus, Profinet, Ethernet Powerlink, EtherNet TCP/IP, Modbus, DeviceNet, CANopen, EtherCAT, Endat and Hiperface, depending on the manufacturer of the device.
    The two output wave forms are 90 degrees out of phase, which is what quadrature means. These signals are decoded to produce a count up pulse or a count down pulse. For decoding in software, the A & B outputs are read by software, either via an interrupt on any edge or polling, and the above table is used to decode the direction. For example, if the last value was 00 and the current value is 01, the device has moved one half step in the clockwise direction. The mechanical types would be debounced first by requiring that the same (valid) value be read a certain number of times before recognizing a state change.
    On encoders with detents there are different ways to switch states. In some, both A and B are always open circuit at the detents, and an entire 00 → 00 switching cycle occurs while transitioning from one detent to the next. Others have detents of alternating 00 and 11 value, with staggered switching times during the transition between detents.

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