Method of Determining A Direction of Rotation and Valid Transitions of Quadrature Pulses

A non-transitory computer-readable medium having a sequence of program instructions which, when executed by a processor, perform a method of determining a direction of rotation of a shaft, said method comprising:

• receiving a first binary signal and a second binary signal from a transducer attached to the shaft, said first and second binary signals being in quadrature;
• determining a present quadrant identification number, QIDPRESENT, as a two-digit binary number by left-shifting a value of said first signal and adding a value of said second signal;
• after a sampling interval has elapsed, setting a past quadrant identification number, QIDPAST, to the value of said QIDPRESENT, determining a new value of QIDPRESENT and calculating a value of a transition code using an equation that operates on QIDPRESENT and QIDPAST;
• and
• responsive to determining that said transition code is valid, using said transition code to determine a direction of rotation of the shaft.

An integrated circuit comprising:

• a pulse width modulation (PWM) driver (206) operable to provide PWM signals for controlling a motor (202);
• connections (for QEP_A, QEP_B) operable to receive a first binary signal and a second binary signal from a transducer (212) attached to a shaft of the motor;
• and
• a feed-back loop (214, 228, 230, 218, 220, 222, 224, 226, etc.) connected between said connections and said PWM driver, said feed-back loop comprising a sequence of program instructions which, when executed by a processor, perform a method of determining a direction of rotation of a shaft, the method comprising:
• determining a present quadrant identification number, QIDPRESENT, as a two-digit binary number by left-shifting a value of said first signal and adding a value of said second signal,
• after a sampling interval has elapsed, setting a past quadrant identification number, QIDPAST, to the value of said QIDPRESENT, determining a new value of QIDPRESENT and calculating a value of a transition code using an equation that operates on QIDPRESENT and QIDPAST, and
• responsive to determining that said transition code is valid, using said transition code to determine a direction of rotation of the shaft.