Abstract:
The invention is a method of controlling a microstepping motor. The method begins with the initialization of a logic circuit in accordance with the requirements of a profile/index bit generated by a microcontroller. An initial stage is established for the logic circuit and determining whether or not to run the motor in stand-alone or pulse controlled mode. The logic initial stage comprises the initialization of a set of one or more data registers; configuration of interrupts and input/output ports; and, the setting of timer prescales. The method next performs a logic sequence to a motor use profile, a system profile, and a program flow. After completion of the logic sequence, the method performs a step sequence to establish the timing pattern of electrical impulses to be directed to one or more integrated circuits. A predetermined acceleration table is established in a program memory having a set of delay constants, wherein the set of delay constants contain the timing sequences for each step in the motor use profile. The acceleration table is then accessed so as to implement acceleration. The logic circuit returns a delay constant from the acceleration table and places a set of data relative to the delay constant in one or more registers for use by the step sequencing routine. The sequencing step comprises the further step of delivering a timing sequence to the integrated circuit wherein the sequence is further comprised of a set of interrupt service routines, corresponding to a state of the motion profile. Each one of the interrupt service routines reloads a timer with a next delay constant and sends the next delay constant to the integrated circuit before updating the step count.

Description:
RELATED APPLICATIONS  
       [0001]    Reference is made to application Ser. No. ______ entitled a LOW COST ⅛th, {fraction (1/16)}th MICRO-STEPPING MOTOR DRIVE SYSTEM, assigned to the assignee of this application and filed on even date herewith. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates generally to the field of motor drive systems utilized for driving office equipment and/or media feed systems; and, more specifically, to the field of micro-stepping motors and motor control torque resonance and acoustic noise reduction.  
         BACKGROUND OF THE INVENTION  
         [0003]    Though there are motors of varied kind, shape and configuration within the equipment that serves our daily lives (everything from office equipment to cameras), they all serve the basic purpose of converting electrical energy into mechanical energy to drive a system component. One segment of this diverse motor population is represented by the group referred to as “stepper motors”. These motors convert a series of electrical pulses into rotational movements of specific duration. The movement resulting from each pulse is consistent both in time and space, thus making stepper motors an ideal means for positioning objects or media.  
           [0004]    One example of the use of a stepper motor to accurately and consistently position an object is disclosed in U.S. Pat. No. 5,410,338 for a Method And Apparatus For Moving An Object With Uniform Motion, issued Apr. 25, 1995 to Jadrich et al. (hereinafter referred to as “Jadrich”). Jadrich discloses an apparatus for printing an image to an object. The apparatus comprises a lead screw adapted to move the object to be printed upon and a stepper motor adapted to rotate the lead screw in a series of rotational steps wherein each step was less than that of the lead screw. Thus, Jadrich is an excellent example of a drive need that is successfully met by the use of a stepper motor. In this case, the lead screw, for each revolution, possessed a predetermined pattern of relationships between an amount of displacement of the object and each step of the stepper motor.  
           [0005]    Another example of the use of stepper motors is provided by U.S. Pat. No. 5,852,354 for a Mutiplexing Rate Generator/Counter Circuit For Controlling Stepper Motors issued Dec. 22, 1998 to J. Randolph Andrews (hereinafter referred to as “Andrews”). In Andrews, a multiplexing circuit was provided so that up to sixteen different stepping motors could share a single rate generator.  
           [0006]    As the stepper motor population group diversified with the myriad applications that the motor population could serve, stepper motors were modified and redefined through control of the circuits that guide the electrical impulses that drive the motors. One of the early problems that led to such modification was the determination that when the motor was running at conventional full or half-step mode, there was a significant increase in noise level and torque resonance. The answer to the problem was found in “micro-stepping” the motor.  
           [0007]    The increase in noise and torque resonance are a byproduct of the conventional stepper motor design. Permanent magnet type stepper motors generally comprise coil windings, magnetically conductive stators and a permanent magnet rotor. An electromagnetic field having opposite poles (a north and a south pole) is created when the coil winding is energized. The magnetic field is carried by the magnetically conductive stators, thus causing the rotor to align itself with the magnetic field. The field, in turn, can be shifted by “stepping” (through sequentially energizing) the stator coils to generate a rotary motion. Various forms of stepping exist; these include: “one phase on” and “two phase on” stepping, as well as half-stepping.  
           [0008]    Half-stepping occurs when an “off” state is inserted between transitioning phases, thus cutting the stepper motor&#39;s full step angle in half. Half stepping, however, results in a loss of torque compared to other forms of stepping such as “two phase on”. The loss of torque is the result of one of the coil windings not being energized during alternate half steps, thus reducing the electromagnetic force being exerted on the rotor.  
           [0009]    Coil windings too, can be of varied type such as “bipolar” or “unipolar” winding. In bipolar coil winding, each phase consists of a single winding. If the current flow in the windings is reversed through switching, then the electromagnetic polarity of the phase is reversed. Unipolar winding, on the other hand, consists of two windings on a common pole. The opposite poles are created when the separate windings are energized. In unipolar winding, the electromagnetic polarity from the drive to the coil windings is not reversed as is the case with bipolar windings. Unipolar windings though, produce less torque than their bipolar counterparts because the energized coil only utilizes half as much of the conductive winding (typically copper).  
           [0010]    In addition to problems with torque in its many forms, stepper motors generate a resonant frequency as a result of their basic spring-mass configurations. When the motor&#39;s step rate equals the motor&#39;s natural frequency, there is an increase in the noise level of the motor as well as an increase in motor vibration. In addition to the increased noise burden on system users, continued vibration can weaken the system structure and efficiency.  
           [0011]    Changing the step rate or microstepping the motor are the two most common means of reducing resonance problems. Microstepping divides a full step into smaller steps and helps reduce noise levels and produce smoother output motion in addition to reducing resonance.  
           [0012]    The microstepping of a motor has been disclosed in the prior art with reference to the addressing of specific needs. Such a need is answered in U.S. Pat. No. 5,359,271 for a Microstepping Bipolar Stepping Motor Controller For Document Positioning issued Oct. 25, 1994 to Frederick K. Husher (hereinafter referred to as “Husher”). In Husher, one object of the invention was to provide an inexpensive controller that could drive a stepping motor in a microstep mode while yielding a multiple of defined position steps as compared to the number of physical motor poles.  
           [0013]    Another need answered by microstepping a motor is disclosed in U.S. Pat. No. 4,710,691 for a Process And Apparatus For Characterizing And Controlling A Synchronous Motor In Microstepper Mode issued Dec. 1, 1987 to Bergstrom et al. (hereinafter referred to as “Bergstrom”). Bergstrom discloses the use of motor characterization stored in memory for use as a control of the rotational motion of the stepper motor.  
           [0014]    The prior art, in addressing such issues as resonance and motion control, has still failed to produce a relatively simple drive system that can be easily adapted to a variety of equipment in a simple, yet efficient, way. There exists a need for a low-cost, easily replicable, micro-stepping motor in which the torque resonance and noise levels are reduced over those of prior art motors.  
         SUMMARY OF THE INVENTION  
         [0015]    The invention is a method of controlling a microstepping motor while utilizing a logic circuit. The method comprises a number of steps that begin with initializing the logic circuit in accordance with the requirements of a profile/index bit generated by a microcontroller. This initialization step comprises the further steps of establishing an initial stage for the logic circuit; determining whether or not to run the motor in stand-alone mode; and, if said determination is “NO” then running the motor in pulse controlled mode. The profile/index bit representative of the mode choice is then generated.  
           [0016]    The logic circuit&#39;s initial stage comprises the initialization of a set of one or more data registers; configuration of interrupts in accordance with the motor use profile; configuration of input/output ports in accordance with the system profile; and, the setting of timer prescales.  
           [0017]    The method next performs a logic sequence wherein the sequence determines a motor use profile, a system profile, and a program flow. After completion of the logic sequence, the method performs a step sequence to establish the timing pattern of electrical impulses to be directed to one or more integrated circuits. A predetermined acceleration table is established in a program memory having a set of delay constants, wherein the set of delay constants contain the timing sequences for each step in the motor use profile. The acceleration table is then accessed so as to implement acceleration. The acceleration table is established for each profile and each step mode.  
           [0018]    The logic circuit points to the acceleration table chosen by the profile/index bit and establishes a set of variables according to the step mode and direction. Further, the logic circuit performs a set of three states in the motion profile wherein two of the three states involve acceleration and wherein the remaining one of the three states involves slew.  
           [0019]    The logic circuit returns a delay constant from the acceleration table and places a set of data relative to the delay constant in one or more registers for use by the step sequencing routine.  
           [0020]    The step sequencing step comprises the further step of delivering a timing sequence to the integrated circuit wherein the sequence is further comprised of a set of interrupt service routines, and, wherein each one of the interrupt service routines corresponds to a state of the motion profile. Each one of the interrupt service routines reloads a timer with a next delay constant and sends the next delay constant to the integrated circuit before updating the step count.  
           [0021]    The microcontroller in stand-alone mode will accelerate the motor then slew the motor in accordance with a preprogrammed velocity selected by the profile bit. The microcontroller decelerates the motor to a stop upon a change in the control bits, reads the changed control bits, and performs an action in accordance with the changed control bit configuration. If the mode is a pulse controlled mode, however, then the microcontroller directly correlates a motor velocity to an input pulse signal. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]    [0022]FIG. 1 is a block diagram of the microcontroller of the present invention.  
         [0023]    [0023]FIG. 2A is a flowchart of the initialization performed by the microcontroller at power-up.  
         [0024]    [0024]FIG. 2B is a continuation of the flowchart of FIG. 2A showing the initialization performed by the microcontroller at power-up.  
         [0025]    [0025]FIG. 3A is a flowchart of the control logic flow in the stand-alone mode of the logic circuit utilized to control the micro-stepping motor.  
         [0026]    [0026]FIG. 3B is a continuation of the flowchart of FIG. 3A showing the control logic flow in the stand-alone mode.  
         [0027]    [0027]FIG. 3C is a continuation of the flowchart of FIG. 3B showing the control logic flow in the stand-alone mode.  
         [0028]    [0028]FIG. 3D is a continuation of the flowchart of FIG. 3C showing the control logic flow in the stand-alone mode.  
         [0029]    [0029]FIG. 4A is a flowchart of the control logic flow in the stand-alone mode of the logic circuit utilized to control the micro-stepping motor.  
         [0030]    [0030]FIG. 4B is a continuation of the flowchart of FIG. 4A showing the control logic flow in the stand-alone mode.  
         [0031]    [0031]FIG. 4C is a continuation of the flowchart of FIG. 4B showing the control logic flow in the stand-alone mode.  
         [0032]    [0032]FIG. 4D is a continuation of the flowchart of FIG. 4C showing the control logic flow in the stand-alone mode.  
         [0033]    [0033]FIG. 5A is a flowchart of the step sequencing in the stand-alone mode of the logic circuit utilized to control the micro-stepping motor.  
         [0034]    [0034]FIG. 5B is a continuation of the flowchart of FIG. 5A showing the step sequencing in the stand-alone mode.  
         [0035]    [0035]FIG. 5C is a continuation of the flowchart of FIG. 5B showing the step sequencing in the stand-alone mode.  
         [0036]    [0036]FIG. 6A is a flowchart of the indexed mode of the logic circuit utilized to control the micro-stepping motor.  
         [0037]    [0037]FIG. 6B is a continuation of the flowchart of FIG. 6A showing the indexed mode of the logic circuit.  
         [0038]    [0038]FIG. 6C is a continuation of the flowchart of FIG. 6B showing the indexed mode of the logic circuit. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0039]    Microstepping a motor requires a significant number of electronic circuits to generate all the necessary functions and logic. Implementing these functions and logic in software results in fewer hardware components and reduces the size of as printed circuit boards. A significant software portion of this invention is an intelligent logic and algorithm for accelerating and decelerating a motor to a desired speed without losing its synchronization. The software module takes care of all the necessary control logic such as start/stop, motion direction, ⅛th or {fraction (1/16)}th step selection, short-circuit detection and operation mode.  
         [0040]    Turning to FIG. 1, there is shown a block diagram of the microcontroller utilized to control the stepper motor. The microcontroller  10  (such as the PIC16C63A which is commercially available from Microchip Technology Inc. of Chandler, Ariz.) is used to implement all the necessary logic and functions performed by the microstepping motor drive. The microcontroller  10  takes care of the interface to external devices  20  through six (6) control bits  21 - 26  and outputs step sequences to the mixed signal integrated circuit  30  (I.C.) (such as the A3957 which is commercially available from Allegro Microsystems Inc. of Worcester, Mass.) through ten (10) signal bits. The microcontroller  10  holds all of the required source code in its memory. It operates at 20 MHz clock speed, 200 ns per master clock period. The software module supports motor speeds up to 5000 full-step or 1500 RPM.  
         [0041]    The microcontroller can run in two program modes. Based on the program mode selected by the Profile/Index bit  25 , the microcontroller  10  will accelerate the motor then slew at the preprogrammed velocity selected by the Profile bits  25 . Upon a change in control bits, the microcontroller  10  will decelerate the motor to a stop then look at the control bits to determine the next course of action. In pulse controlled (index) mode, the motor velocity is directly related to the input pulse signal. Every time the microcontroller  10  receives a pulse, it will output a step to the integrated circuit chip  30 . Therefore, the system that sends the pulse signals to the microcontroller  10  would also have to take care of motor acceleration. When set, the latch input bit locks the Direction and Mode.  
                                 TABLE 1                           Control Bits in Profile Mode                Control Bit (s)   Value   Assignment                       Start-Stop   0   Stop               1   Start           Mode   0   {fraction (1/16)}th Step               1   ⅛th Step           Direction   0   cw               1   ccw           Profile1:Profile0   00     500 Fs/sec slew velocity               01    1000 Fs/sec slew velocity               10    2000 Fs/sec slew velocity               11    3000 Fs/sec slew velocity                      
 
         [0042]    [0042]                                 TABLE 2                           Control Bits in Index Mode                Control Bit (s)   Value   Assignment                       Pulse   —   A rising edge tells the microcontroller                   to send out next step           Enable   1   Run motor               0   Disable motor           Latch   1   Inputs latched               0   Inputs not latched           Direction   0   cw               1   ccw           Mode   0   {fraction (1/16)}th step               1   ⅛th step                        
         [0043]    In microstepping, the motor current slowly steps up to the peak current then slowly steps back down. If the proper step sequence is followed, the resulting current waveform should be sinusoidal. Table 3 shows the step sequence for two mode options: ⅛th step and {fraction (1/16)}th step. There are thirty-two (32) steps in the ⅛th step mode and sixty-four (64) steps in the {fraction (1/16)}th step mode. There are two (2) phases to a stepper motor. For each phase, there is a phase enable bit  32  and four D/A bits  31  resulting in a total of ten (10) bits. Since the microcontroller  10  is an 8-bit microcontroller, the ten bits are divided into a group of eight (8) bits and a group of two (2) bits. The group of eight (8) bits consists of D/A bits  31  (A0:A3 for phase A and B0:B3 for phase B). The group of two (2) bits contains the phase enable bits  32 . The columns labeled ‘Hex value’ contain the hexadecimal equivalents to the 8-bit and 2-bit words.  
       Table 3  
     Step Sequence Table  
       [0044]    Table 3 is attached hereto as Attachment 1 following the Detailed Description of the Preferred Embodiments.  
         [0045]    In stand-alone mode, compilation of the acceleration table needs to be completed prior to coding the algorithm. The acceleration table is a list of delay constants that corresponds to delay times. Compilation of the acceleration table requires knowledge of the motor as well as the target velocities of the motor.  
         [0046]    For a 1.8° step motor, 200 full steps result in one revolution of the motor. In {fraction (1/16)}th microsteps per full-step mode, that is equivalent to 3200 microsteps per revolution. This means that for every revolution, the microcontroller  10  needs to send out 3200 sets of 10-bit signals to the integrated circuit  30  or motor drive chips. There are 64 unique sets of these 10-bit signals and they repeat in the order specified by the step table. The velocity of a stepper motor is equal to how fast the motor steps. By controlling the time between sending out signals, the microcontroller  10  can control the velocity of the motor. For example, if the microcontroller  10  sends out one step every millisecond, then the motor will be running at 1000 microsteps/sec (equal to 1/1 ms). The time between steps the is referred to as “delay time”. A table of delay times would be sufficient for an acceleration table. However, since a microcontroller deals with master clock cycles and hexadecimal numbers, the delay times must be converted into hexadecimal delay constants. The delay constant for a given delay time can be determined by the following formula:  
       Delay_Constant:        Delay_Time     Prescale   *   Cycle_Period                             
 
         [0047]    The cycle period is the time it takes for a microcontroller to go through one cycle (With a 20 MHz clock, the cycle period is 0.2 μs). The prescale is a factor to scale down delay constants. With a prescale of 1, a delay time of 1 ms will result in a delay constant of: 
         Delay_Constant=1ms=5000 
         1*2 μs 
         [0048]    A delay constant of 5000 in decimal is equivalent to 1388 in hexadecimal.  
         [0049]    Now turning to FIG. 2A, there is shown a flowchart of the initialization performed by the microcontroller  10  at power-up.  
         [0050]    Upon power-up at step  100 , the microcontroller  10  initializes several registers step  102 , configures interrupts and I/O ports, and sets timer prescales at step  104 . It will then determine whether to run in pulse-controlled mode or stand-alone mode.  
         [0051]    In standalone mode, the software is divided into three sections: control logic, step sequencing, and preprocessed acceleration tables. The logic section determines which profile to run as well as the program flow. The step sequencing section handles the timing involved in sending out signals to the integrated circuit  30 . To implement acceleration, delay constants that contain the timing for each step in the acceleration profile are stored in tables in the program memory. These acceleration tables (one for each profile and step mode) must be calculated by the programmer beforehand and burned into the microcontroller  10  memory.  
         [0052]    The control logic section reads the input control bits, points to the acceleration table chosen by the profile bits, and sets variables according to the mode and direction. The profile being run depends solely on the acceleration table and certain variables. Once these variables are set to the correct values corresponding to the profile, the same algorithm will be used to run each profile. The control section will then flow through the three states in the motion profile. Two of the states involve acceleration, while the third state is slew. The outset of the acceleration tables contain 16-bit delay constants, while the remaining portion of the tables contain 8-bit delay constants. Since the microcontroller 10 is 8-bit, processing of 16-bit constants and 8-bit constants are separated. The main task in each stage is to get delay constants from the acceleration table and place the data in registers for the use of the step sequencing routines.  
         [0053]    The step sequencing algorithm is responsible for the timing at which steps are outputted to the integrated circuit  30 . This algorithm consists of interrupt service routines, one interrupt routine for each state of the motion profile. Each interrupt routine first reloads a timer with the next delay constant, then sends out the next step to the integrated circuit  30 , and finally updates the step count. When the timer reaches ‘00’, an interrupt will occur that will call the service routine again. A step table with the proper step sequence is stored in program memory. It is important that the step count is updated correctly. In indexed mode, the algorithm checks for a rising edge, then sends out a step to the integrated circuit immediately after the rising edge. There is a routine that updates the step count every time a step is sent out.  
         [0054]    Returning to FIG. 2A, the method then advances to step  106  to clear output ports and PCLatch register before disabling all interrupts. The system then stores the configuration at port B in step  108  before advancing along path A to step  110  as is shown in FIG. 2B.  
         [0055]    [0055]FIG. 2B is a continuation of the flowchart of FIG. 2A showing the initialization performed by the microcontroller at power-up. The flow begins with a query at step  110 , which asks if a short circuit is present. If the response to the query is “YES,” then the Reset function is activated; if there is no Short Circuit, then the method advances to the query at step  112 . Step  112  queries as to whether or not a profile mode is in place. If the Profile Mode is not in place, then the method advances to the Indexed Mode at step  114 . If, however, the response to the query at step  112  is “YES,”, then the method advances to step  116  and accesses the profile mode.  
         [0056]    [0056]FIG. 3A is a flowchart of the control logic flow in the stand-alone mode of the logic circuit utilized to control the micro-stepping motor. Commencing with the Profile Mode at step  150 , the method advances to step  152  which queries as to whether or not the motor has performed a stop/start. If the response to the query is “NO,” then the Reset function is activated; if, however, the response to the query is “YES,” then the data registers are reset, re-initialized and the set state is counted at step  154  before proceeding to the home position at step  156 . Once the home position has been established the motor use profile is established at step  158  before advancing to the query at step  160  which asks whether or not the 16 th  step mode is to be utilized. If the response to the query is “YES,” then the timing sequence is set for  16   th  step mode. If, however, the response to the query at step  160  is “NO,”, then the method proceeds to initialize, at step  162 , acceleration counter to print to the first location in the 8 th  step acceleration table. The method advances from step  162  to step  164  which queries as to the motion of the motor. If proceeding in a clockwise direction, then the method advances to step  166  where the direction offset is set at 2, and the count refill is set at 0 before the motor is run. If the motor is to be set in a counterclockwise direction, then the direction offset is set at O*FE and the step count refill is set at 3E.  
         [0057]    Turning next to FIG. 3B there is shown a continuation of the flowchart of FIG. 3A showing the control logic flow in the stand-alone mode. The method proceeds in the 16 th  step mode to initialize the acceleration count to point to a first location in the 16 th  step acceleration table at step  170 . The method advances from step  170  to step  172  where the method queries as to the rotation of the motor. If the motor is to move in a clockwise direction, then the direction offset is set at 1 and the step count refill is set at 0 in step  174  before advancing to step  178 . If the motor movement is in a counterclockwise direction, then the direction offset is set at 0xFF and the step count refill is set at 3F in step  176  before advancing to step  178 . At step  178 , the motor is run and a delay count taken before proceeding to the timing of the load at step  180 . From step  180 , the method advances to step  182  where the output phase and analog to digital (A/D) signals are passed to the motor before proceeding to initialize Timer  1  and trigger the interrupt at step  184 . The step count is then updated and the next sequence is sought before advancing along path A to step  190  as is shown in FIG. 3C.  
         [0058]    [0058]FIG. 3C is a continuation of the flowchart of FIG. 3B showing the control logic flow in the stand-alone mode. Path A is shown re-entering the method flow at step  190  where the timer set flag is cleared before proceeding to the acceleration count at step  192 . From step  192 , the method advances to step  194  where the High Byte is to be stored. From step  194 , the method advances to step  196  where if the High Byte is at 0, then the method proceeds to the 1 Byte Count. If High Byte is not set at 0, then the method proceeds to the 16 th  Step acceleration count at step  198  before proceeding store the Low Byte at step  200 . The method advances from step  200  to a query at step  202  which asks if the timer flag has been set. If it is not set, then the method re-enters the method flow at step  202   200 . However, if the timer flag is set, then the method returns to clear the timer set flag at step  190 .  
         [0059]    Looking at FIG. 3D which is a continuation of the flowchart of FIG. 3C showing the control logic flow in the stand-alone mode, the method proceeds from the lByte count initialization. The method proceeds to step  206  where the motion state is incremented so as to get the Low Byte and High Byte of the next delay count at step  208 . From step  208 , the method advances to step  210  where the second level of buffer is prepared. The Low byte and the High Byte are obtained next and stored in a data place holder. The method proceeds to step  212  to check if the timer flag has been set. If the timer flag is not set, then the flow returns to enter before step  212 . If the timer flag is set, then the method proceeds to the Enable Timer 0  Interrupt and Disable Timer 1  Interrupt acctions at step  214 .  
         [0060]    The timer set flag is cleared at step  216  and the method advances to get the next Low Byte and High Byte and place them in the holder at step  218 . If the High Byte is at 0 in step  220 , then the method proceeds to SLEW. If not, then the method queries, at step  222 , as to whether or not the timer flag is set. If the Timer Flag is not set, then the flow returns to step  220 ; if the timer flag is set, then the method returns to step  216 .  
         [0061]    [0061]FIG. 4A is a flowchart of the control logic flow in the stand-alone mode of the logic circuit utilized to control the micro-stepping motor. The flow of FIG. 4A details the SLEW routine. From the routine opening, the method advances to step  230  which queries as to whether or not the timer flag is set. If the response to the query is “NO,” then the method returns to re-enter the flow at step  230 . However, if the response to the query at step  230  is “YES,” then the method continues on to step  232  where the phase state of the motor is incremented. The method advances from step  232  to step  234  where the Flasher LED bit is set and timerl registers are cleared. At step  236  the acceleration count is decremented and the previous High Byte and the Low Byte are obtained at step  238  and stored in their place holder. If there is no PORTB change for step  240 , then the method returns to the method flow at step  240 , if there is a change in PORTB, then deceleration of 1 Byte occurs as is shown in FIG. 4B.  
         [0062]    Turning to FIG. 4B which is a continuation of the flowchart of FIG. 4A showing the control logic flow in the stand-alone mode, from the Decel 1 Byte step, the method proceeds to load the Low Byte and the High Byte with the next delay constant at step  242  before the state is decremented at step  244 . The method then advances to step  246  where the timer set flag is cleared and the next High Byte is obtained and stored in the appropriate place holder at step  248 . If the High byte is at 0, then the decel 2 Byte routine will be employed as is shown in FIG. 4C; if the High Byte is not at 0, then the next Low Byte is obtained at step  252  and stored in the holder before the method proceeds to check the timer flag at step  254 . If the timer flag is not set, then the flow returns at step  254 ; if the timer flag is set, then the method returns to step  246 .  
         [0063]    Turning to FIG. 4C which is a continuation of the flowchart of FIG. 4B showing the control logic flow in the stand-alone mode and the decel 2 Byte routine in particular. If the timer flag is not set at step  260 , then the flow re-enters the path at step  260 ; if the timer flag is set, then the method continues to decrement the state at step  262  before advancing to get the next Low Byte and high byte at step  264 . The timer set flag is cleared at step  266 . The timer flag is checked at step  268 ; and, if it is not set, then the flow returns to re-enter at step  268 . If the flag is set, then disable the Timer0 interrupt and Enable Timer1 interrupt at step  270 , the the timer set flag is cleared at step  272  and the next Low Byte and High Byte are obtained at step  274 . Once again, the the timer flag is checked at step  276 ; and, if it is not set, the flow returns to step  274 ; if the flag is set, then the method proceeds to a deceleration query at step  278 . If the response to the query is “NO,” then the timer set lag is cleared at step  272 ; however, if the response to the query is “YES,” then the method waits for the Timer to expire at step  280  prior to reset  280 .  
         [0064]    [0064]FIG. 4D is a continuation of the flowchart of FIG. 4C showing the control logic flow in the stand-alone mode. The flow begins at step  290  where the acceleration count is incremented. The method completes the incrementation at step  292 . The method then advances to step  294  where the method queries as to the presence of any overflow before advancing to step  296  where an increment of the acceleration count occurs. The delay count is obtained at step  298  before proceeding to the return at step  300 .  
         [0065]    Decrementation of the acceleration count occurs at step  306 . The method completes the incrementation at step  308 . The method then advances to step  310  where the method queries as to the presence of any overflow before advancing to step  312  where an decrement of the acceleration count occurs. The delay count is obtained at step  314  before proceeding to the return at step  300 .  
         [0066]    Now turning to FIG. 5A, there is shown a flowchart of the step sequencing in the stand-alone mode of the logic circuit utilized to control the micro-stepping motor at ISR step  350 . The process proceeds to Store w., Status, and PCLATCH registers at step  352 , then to clear PCLATCH at step  354 . At step  356 , there is a query as to whether S.C Interrupt Set. If the answer to the query at step  356  is “Yes”, the process proceeds to Reset. If the answer to the query at step  356  is “No”, the process goes to step  358  to a query to State  0 , State  1  or State  2 . If the answer to the query at step  356  is State  0 , the process proceeds to Load Timer 1  and Output Step Sequence at step  370 , and then to Set timer Set Flag and Clear timer 1  and Timer 0  Interrupt flag at step  372 , and then to Upd Step Count at step  374 . If the answer to the query at step  358  is State  1 , the process goes to Load timer) and Output Step Sequence at step  360 , and then to Decrement High Byte at step  362  and then to B. If the answer to the query at step  358  is State  2 , the process proceeds to Load timer 0  and Output step Sequence at step  364 , then to Clear timer 0  Interrupt Flag at step  366 , and then to Upd Step Count at step  368 .  
         [0067]    Now turning to FIG. 5B, there is shown a continuation of the flowchart of FIG. 5A showing the step sequencing in the stand-alone mode from B following step  362  as shown in FIG. 5A. From B, the process proceeds to the query High Byte=0? at step  380 . If the answer to the query at step  380  is “Yes”, the process proceeds to Load Next High Byte and Low byte from Holder at Step  382 , then to Set Timer Set Flag at step  384 , then to Point to next step at step  386 . If the answer to the query at step  380  is “No”, the process proceeds to Point to next step at step  386 . Proceeding from step  386 , the process continues to Get Step Sequence at step  388 , then Clear timer 0  and timer 1  Interrupt Flag at step  390 . From step  390 , the process continues to Restore W, Status, and PCLATCH registers at step  392  then to Return at step  394 .  
         [0068]    Now turning to FIG. 5C, there is shown a continuation of the flowchart of FIG. 5B showing the step sequencing in the stand-alone mode. From Upd Step Count  400 , the process proceeds to Add Direction Offset to Step Count  402 . At step  404 , there is a query as to whether there is an overflow. If the answer to the query at step  404  is “Yes”, the process proceeds to Load step Count Refill to Step Count  406 , and then to Get Step Sequence  408 , then to Restore W. Status, and PCLATCH registers  410  and then to Return  412 . If the answer to the query at step  404  is “No”, the process proceeds to Get Step Sequence  408 , then to Restore W. Status, and PCLATCH registers  410  and then to Return  412 .  
         [0069]    Turning now to FIG. 6A, there is shown a flowchart of the indexed mode of the logic circuit utilized to control the micro-stepping motor at indexed mode  420 . The process proceeds to Clear I/O ports and set data direction of I/O ports  422  and then to Initialize Step Count  424 . Then the process proceeds to Home Motor for 1 second  426 , and then to Clear I/O ports  428 . From step  428 , the process proceeds to clear registers  420  and then to Store control bits  432 . At step  434 , there is a query as to whether there is a short circuit. If the answer to the query at step  434  is “Yes”, the process proceeds to Reset. If the answer to the query at step  434  is “No”, the process proceeds to step  436  to a query as to whether the inputs latched. If the answer to the query at step  436  is “No”, the process proceeds to Reset. If the answer to the query at step  436  is “Yes”, the process proceeds to determine Mode and Direction  438 , then to Set registers based on direction and mode  440 , and then to Run Motor  442 .  
         [0070]    Now turning to FIG. 6B, there is shown a continuation of the flowchart of FIG. 6A showing the indexed mode of the of the logic circuit beginning at Run Motor  450 , and continuing to Update Step County  452 . At step  454 , if the update step count is enabled, the process proceeds to step  456 . If, at step  454 , the update step count is not enabled, the process returns to step  452 .  
         [0071]    If the process is enabled at step  454  and proceeds to step  456 , the process is queried as to whether to close High . If the answer to the query is “Yes”, then the process proceeds to output A/D and Phase step  458 . If the answer to the query at step  456  is “no”, then the process returns to step  452 . Continuing from output A/D and phase step  458 , the process proceeds to update step count  460  and then to step  462  where it is queried as to whether the motor is disabled. If the answer to the query at step  462  is “Yes”, the process proceeds to Home Motor. If the answer to the query at step  462  is “No”, the process proceeds to step  464  where it is queried as to whether the clk low. If the answer to the query at step  464  is “Yes”, the process proceeds to Loop 1 . If the answer to the query at step  464  is “No”, the process terminates.  
         [0072]    Now turning to FIG. 6C, there is shown a continuation of the flowchart of FIG. 6B showing the indexed mode of the logic circuit. From the Update Step Count  470 , the process proceeds to Add DIRECTION OFFSET to STEP COUNT  474 . At Overflow  474 , the process queries if there is an overflow. If the answer to the query at Overflow  474  is “Yes”, the process proceeds to Load SET COUNT REFILL and store to STEP COUNT  476  and then to Get A/D and Phase from Step Table  478  and ends at Return  480 . If the answer to the query at Overflow  474  is “No”, the process goes to Get A/D and Phase from Step Table  478  and ends at Return  480 .  
         [0073]    While certain embodiments have been described above in terms of the system within which the method may reside, the invention is not limited to such a context.  
         [0074]    In the foregoing specification, the invention has been described with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.  
                                                                                               TABLE 3                           Step Sequence Table            Step       Hex       Hex            ⅛   {fraction (1/16)}   A3   A2   A1   A0   B3   B2   B1   B0   value   Phase A   Phase B   value                1    1   1   1   1   1   0   0   0   0   F0   1   X   03            2   1   1   1   1   0   0   1   0   F2   1   1   03        2    3   1   1   1   1   0   0   1   1   F3   1   1   03            4   1   1   1   0   0   1   0   0   E4   1   1   03        3    5   1   1   0   1   0   1   0   1   D5   1   1   03            6   1   1   0   0   0   1   1   0   C6   1   1   03        4    7   1   0   1   1   0   1   1   1   B7   1   1   03            8   1   0   1   0   1   0   0   0   A8   1   1   03        5    9   1   0   0   1   1   0   0   1   99   1   1   03           10   1   0   0   0   1   0   1   0   8A   1   1   03        6   11   0   1   1   1   1   0   1   1   7B   1   1   03           12   0   1   1   0   1   1   0   0   6C   1   1   03        7   13   0   1   0   1   1   1   0   1   5D   1   1   03           14   0   1   0   0   1   1   1   0   4E   1   1   03        8   15   0   0   1   1   1   1   1   1   3F   1   1   03           16   0   0   1   0   1   1   1   1   2F   1   1   03        9   17   0   0   0   0   1   1   1   1   0F   X   1   01           18   0   0   1   0   1   1   1   1   2F   0   1   01       10   19   0   0   1   1   1   1   1   1   3F   0   1   01           20   0   1   0   0   1   1   1   0   4E   0   1   01       11   21   0   1   0   1   1   1   0   1   5D   0   1   01           22   0   1   1   0   1   1   0   0   6C   0   1   01       12   23   0   1   1   1   1   0   1   1   7B   0   1   01           24   1   0   0   0   1   0   1   0   8A   0   1   01       13   25   1   0   0   1   1   0   0   1   99   0   1   01           26   1   0   1   0   1   0   0   0   A8   0   1   01       14   27   1   0   1   1   0   1   1   1   B7   0   1   01           28   1   1   0   0   0   1   1   0   C6   0   1   01       15   29   1   1   0   1   0   1   0   1   D5   0   1   01           30   1   1   1   0   0   1   0   0   E4   0   1   01       16   31   1   1   1   1   0   0   1   1   F3   0   1   01           32   1   1   1   1   0   0   1   0   F2   0   1   01       17   33   1   1   1   1   0   0   0   0   F0   0   X   00           34   1   1   1   1   0   0   1   0   F2   0   0   00       18   35   1   1   1   1   0   0   1   1   F3   0   0   00           36   1   1   1   0   0   1   0   0   E4   0   0   00       19   37   1   1   0   1   0   1   0   1   D5   0   0   00           38   1   1   0   0   0   1   1   0   C6   0   0   00       20   39   1   0   1   1   0   1   1   1   B7   0   0   00           40   1   0   1   0   1   0   0   0   A8   0   0   00       21   41   1   0   0   1   1   0   0   1   99   0   0   00           42   1   0   0   0   1   0   1   0   8A   0   0   00       22   43   0   1   1   1   1   0   1   1   7B   0   0   00           44   0   1   1   0   1   1   0   0   6C   0   0   00       23   45   0   1   0   1   1   1   0   1   5D   0   0   00           46   0   1   0   0   1   1   1   0   4E   0   0   00       24   47   0   0   1   1   1   1   1   1   3F   0   0   00           48   0   0   1   0   1   1   1   1   2F   0   0   00       25   49   0   0   0   0   1   1   1   1   0F   X   0   02           50   0   0   1   0   1   1   1   1   2F   1   0   02       26   51   0   0   1   1   1   1   1   1   3F   1   0   02           52   0   1   0   0   1   1   1   0   4E   1   0   02       27   53   0   1   0   1   1   1   0   1   5D   1   0   02           54   0   1   1   0   1   1   0   0   6C   1   0   02       28   55   0   1   1   1   1   0   1   1   7B   1   0   02           56   1   0   0   0   1   0   1   0   8A   1   0   02       29   57   1   0   0   1   1   0   0   1   99   1   0   02           58   1   0   1   0   1   0   0   0   A8   1   0   02       30   59   1   0   1   1   0   1   1   1   B7   1   0   02           60   1   1   0   0   0   1   1   0   C6   1   0   02       31   61   1   1   0   1   0   1   0   1   D5   1   0   02           62   1   1   1   0   0   1   0   0   E4   1   0   02       32   63   1   1   1   1   0   0   1   1   F3   1   0   02           64   1   1   1   1   0   0   1   0   F2   1   0   02