【正文】 of the H bridge are made on in the next oscillator cycle.III. LOGIC CIRCUIT DESIGNINGIn any mode of operations, wave patterns of A, B, C and D phases of the L297 repeat after four clock cycles as shown in . Translation of the repetition of the phase waveform after the ten clock cycles is essential to derive the drive topology for the five phase stepper motor.Fig. . In the normal operation, L297 two phases of a 4 phase stepper motor or two ends of a 2 phase stepper motor winding are made ON at a time and the sequence repeats after every 4 clock cyclesBy analyzing the three modes of operations of the L297, it is clear that in the normal drive mode, which is usually called as twophaseon drive mode, should be selected to achieve the required excitation sequence for a 5 phase stepper motor as shown in the .By studying the required excitation sequence for 5 phase stepper motor and A, B, C, D phase sequences of the L297, the required logic circuit was designed. The procedure mentioned below was followed.Fig. . Five phase excitation sequence (i) Separation of High and Low side transistor excitation pattern for each phase from five phase excitation sequences as shown in .(ii) Selection of suitable phases from A, B, C and D of L297 to generate the high side excitation sequences.(iii) Generating input signals to the L298N using A, B, C, D output signals of the microcontroller and the relevant AND gates.(iv)Create ENA (enable A) and ENB (enable B) signals for L298NBy dividing ten (10) steps of required phase pattern in to twenty (20) steps can be equated to the four clock cycles of output wave pattern generated by the L297. The explains the clock cycle selection for required high and low side excitation sequence.Fig. . Required High and Low side transistor excitation sequencesHigh side transistor excitation sequence can be generated from L297 by selecting suitable output phases of the L297. The selected order, which is the twophaseon mode of L297 is shown in the .The microcontroller signals are used to generate the required high side pulse patterns. The DM74LS08 Quad 2Input AND Gates are used to AND microcontroller signals and signals received from L297.Fig. . Generation of Input signals to the L298NAs shown in , the input signals and Enable signals determine the high side and low side transistor switching patterns. Therefore ENABLED (EN) signals are fed from the microcontroller. But to achieve current control of the motor INH signal must engaged with the Enabled signal to the L298N as explained under current control section. The L298N consists with Hbridges and one output of a bridge was used for a phase. Two inputs of one H bridge is dependent each other. Therefore both outputs of a single bridge cannot be used. To generate five phases, it is required to have three numbers of L298N dual full bridge driver ICs. The selection of inputs and outputs of L298N are shown in of Section IV.Fig. . Pull up and Pull down operation of L298NIV. INTERFACE DESIGNINGThe logic circuitry used to generate required input signals for L298N and microcontroller control signals play a major role in the driver circuit. The shows interface of L297, DM74LS08 Quad 2Input AND Gates ICs and L298N with the microcontroller PIC16F877A.The circuit configuration for L297 is shown in . The control signal has to be grounded to obtain the inhibit control mode in order to limit the current through the motor windings. The CLOCK signal is supplied by the microcontroller and HALF/FULL pin should always to be low for full mode (twophaseon) of operation. The ENABLED signal is used to control the motion of the motor. When it is low, all INH1, INH2, A, B, C, D pins are brought to low. The Vref value sets the current flowing through the motor. There are two L297 ICs used and it is necessary to synchronize them. It can be done easily by using the SYNC pin of L297.Fig. . Block diagram of the systemThe shows how the input and output terminals are used in L298N. Usually 100nF noninductive capacitors are used between both Vs and Vc with the ground. The value of the current sensing resistor has to be as small as in order to avoid large voltage drops at large currents.External diode bridges provide current circulating paths when the inputs of the IC are chopped. Usually Schottky diodes are used here because they are faster in recovery.V. RESULTSThe theoretical and logical analysis of the stepper drive circuit design approach shows that it is a simple construction having several modes of operation and control.The performance of the stepper drive circuit shown in the was tested for the following capabilities:1. Speed control capability2. Current control capabilityThe and show the excitation wave forms at each phase terminal. The excitation sequences for all five phases reveal that they are working according to the requirement. shows additional orange and green phase excitation sequences to pare the black phase excitation with the others. Due to the charging and the discharging of the capacitors by the current flowing through the windings of the motor, there are some transients at each excitation points.The speed control of the motor has been achieved by varying the frequency of the excitation sequence of the five terminals. It is clearly shown that the pulse width of the voltage sequences of , gets doubled in the , same time scale of 5ms/div. It is observed that the rotating speed (speed 1) of the motor relevant to the excitation sequence shown in is half that of the speed (speed 2) of the excitation sequence shown in . Hence by varying the pulse frequency of the excitation sequence generated by the PIC microcontroller, the speed of the motor can be varied.Fig. . Drive circuit with microcontroller Voltages of the Blue, Red, Orange and Green phases at speed 1. Voltages of the Orange, Green and Black phases at speed 1. Vo