c minus the signal of fig4 b shown on an enlarged scale in fig4 d as in fig4 c each vertical step in the signal corresponds to a commutation or step pulse generated on output terminal 20 of control logic 12 a curve 80 is drawn onto the plot of fig4 d to illustrate the magnitude of the error at each motor commutation returning again to fig3 after the error computation is performed in box 60 comparison is made to determine whether or not u03c6error is greater than u03c6reference with the result being placed on conductor 44 in fig1 if u03c6error is greater than u03c6reference then the rotor has not yet reached the switching angle determined by u03c6reference and is not yet ready to be commutated again control then transfers to box 66 in which v min counter the value of which appears on conductor 46 is examined to see whether or not it exceeds zero as will be recalled v min is an integer which determines the minimum commutation rate and thus the minimum velocity of motor 26 even if the rotor has not reached the switching angle determined by u03c6reference it may be necessary to commutate it in order to maintain the minimum commutation rate if v min counter gt 0 i e it is not necessary to step the motor to maintain the minimum rate control returns again to box 56 to wait for the clock pulse returning again to box 62 if u03c6error is not greater than u03c6reference control passes to box 64 the value of counter v in appears on conductor 48 in fig1 as.