Interfacing a Stepper Motor to the MB90F598 Microcontroller
Contents
1. In terms of steps the required position which may be obtained from an input sensor is set in the variable uiRequiredPosition This variable is updated by the reload timer interrupt service routine until the requested position is unequal to the current position of the rotor When the inequality is seen then the motor still has not attained its required position The selector registers are used to determine which quadrant of the motor needs to get magnetic flux For a simple two pole two coil stepper motor there are four different positions that the rotor can be in Depending on the quadrant of the rotor programming the compare registers and the selector register brings about movement of the stepper motor rotor Only one of the four outputs is being controlled that is only one connected stepper motor The four possible quadrants to be programmed for this motor can be found by selecting P1 and M1 from the PWS1 and PWS2 select registers The bit numbers that need to be programmed are 1 4 9 and 12 The four mutually exclusive quadrants can then be expressed as shown in Tables 4 and 5 Table 4 PWM Selector Register Bits PWS10_Mi PWS10_P1 PWS20_M1 PWS20 P1 COIL2 COIL1 0 1 0 1 POS POS 0 1 1 0 NEG POS 1 0 1 0 NEG NEG 1 0 0 1 POS NEG The four quadrants and their corresponding values then can be detailed as Table 5 Quadrant Values Name Binary Value Note Bits 1 4 9 12 Hex Value PWS_QI 0001 0000 002. X X The contents of the two 8 bit compare registers determine the widths of PWM pulses The stored value of OOH represents the PWM duty of 0 and FFH represents the duty of 99 6 One PWM Cycle 256 Input Clock Cycles Register Value e 00h a a 80h 128 Input Clock Cycles FFh 255 Input Clock Cycles These registers are accessible at any time However the modified values are reflected to the pulse width at the end of the current PWM cycle after the BS bit of the PWM2 select register is set to 1 3 PWM 1 and 2 Select Register PWM1 Select Register Address 000072h 7 6 5 4 3 2 1 0 lt 3 Bit Number E ee P PE e ao o aSa Read Write c gt RW RW RW RW RAW RW Initial Value gt 0 0 0 0 0 0 PWM2 Select Register Address 000073h 15 14 1 1 10 9 8 lt 3 Bit Number 2 3 12 es pe pi Po m m mo Pws Read Write c gt R W R W RAW RAW RW R W RW Initial Value gt 0 0 0 0 0 0 0 Fujitsu Microelectronics Inc 9 Interfacing a olepper Motor to the MBSOFOSS Microcontroller bit 14 BS Update bit This bit is set to synchronize the settings for the PWM outputs Any modifications in the two compare registers and two select registers are not reflected at the output signals until this bit is set When this bit is set to 1 the PWM pulse generators and selectors load the register contents at the end of t
3. 01 0000 0x1010 PWS_AQll 0000 0010 0001 0000 0x0210 PWS_AIII 0000 0010 0000 0010 0x0202 PWS_QIV 0001 0000 0000 0010 0x1002 Thus PWS_Q1 PWS_QII PWS_QIII and PWS_QIV are the values that are programmed into the select registers based on the quadrant The contents of the compare registers determine the width of the PWM pulses To achieve smoothness and to account for the capabilities of the physical motor the 256 possible values are broken down into a smooth distribution of 32 values These values determine the 32 different steps that the motor can make in any given quadrant Combining these 32 different step values with the appropriate quadrant selection can achieve smooth rotor motion for an entire rotation with 128 32 4 steps of the motor The two compare registers that control the duty cycle on the two coils of the motor are always programmed so that the sum of the two values is equal to OxFE To make this programming easier a lookup table of 32 values one for each step is set up as follows unsigned char LookupTable 32 0 13 25 37 50 62 74 86 98 109 120 131 142 152 162 1 71 180 189 197 205 212 219 225 231 236 240 244 247 250 252 254 255 i Fujitsu Microelectronics Inc 11 Interfacing a olepper Motor to the MBSOrHSS Microcontroller Thus in pseudo code the programming of the compare and select registers for the first quadrant would look like TableIndex PositionDesired amp Ox1F 2 to the power 5 32 s
4. a 16 bit MB90F598 flash microcontroller evaluation board A description is given on how to connect the evaluation board to a stepper motor and run the demo program This document also describes the source code for the simple control firmware the project file for the SOFTUNE development environment and the programming instructions for storing the control code in the flash memory on the microcontroller For information on how to order this evaluation board visit our web site at www fujitsumicro com 4 Fujitsu Microelectronics Inc Orientation on Stepper Motors A direct current DC motor runs by itself when voltage is supplied to it Ina DC motor a split ring commutator switches the direction of the current through the magnetic field coils each half rotation to maintain the shaft s direction of motion A stepper motor can be viewed as an electric motor without a commutator All windings in the stepper motor are part of the stator The rotor is a permanent magnet or in the case of variable reluctance motors a toothed block of some magnetically soft material All of the commutation is handled externally by the motor controller Typically the motor and controller are designed so that the motor can be held in any fixed position as well as rotated one way or the other With the appropriate controller a stepper motor can start and stop on a dime at controlled orientations The repeatability of positioning with a stepper moto
5. ach pair of motor poles is more complex Figure 2 Bipolar Permanent Magnet and Hybrid Motors Stepper motors come in a wide range of angular resolutions The coarsest motors typically turn 90 degrees per step whereas high resolution permanent magnet motors can commonly handle 1 8 or even 0 72 degrees per step With the appropriate controller most permanent magnet and hybrid motors can be run in half steps and some controllers can handle smaller fractional steps or microsteps For permanent magnet and variable reluctance stepper motors when one winding of the motor is energized the rotor under no load snaps to a fixed angle It holds that angle until the torque exceeds the holding torque of the motor at which point the rotor turns trying to hold at each successive equilibrium point Driving Scheme for a Bipolar Stepper Motor An electrical drive is required to properly control a bipolar stepper motor Its functions include start stop reverse and velocity changes Stepper motors translate digital switching sequences into motion The driving magnetic field rotates as magnetic coils are switched on and off This pushes and pulls at permanent magnets arranged around the edge of a rotor that drives the output shaft The drive circuitry for a bipolar stepper motor requires an H bridge control circuit for each winding An H bridge allows the polarity of the power applied to each end of each winding to be controlled independen
6. at the reload timer interrupt service routine is used to update the position of the stepper motor The ISR programs the compare registers and then sets the output enable bits in the control register to drive the external pins The value for the time period of the reload timer interrupt is chosen so that smooth movement is achieved The following code illustrates position control by setting the required parameters in the control program Control the rotor of one of the stepper motors void TestStepperMotor_0 void unsigned long ctr unsigned long ctr2 DDR4_D40 1 PDR4_P40 1 DDR4_D47 1 PDR4_P47 0 uiMaxSpeed 1 Controls the speed of the motor for ctr 500000L ctr ctr uiRequiredPosition MAX_STEPS MAX_STEPS is the maximum no of steps the motor can move in either direction for ctr 700000L ctr ctr uiRequiredPosition 0 while uiCurrentPosition uiRequiredPosition for ctr 700000L ctr ctr uiRequiredPosition 1000 while uiCurrentPosition uiRequiredPosition for ctr 700000L ctr ctr uiRequiredPosition 2000 while uiCurrentPosition uiRequiredPosition for ctr 700000 ctr ctr uiRequiredPosition 1500 while uiCurrentPosition uiRequiredPosition for ctr 700000L ctr ctr uiRequiredPosition 500 while uiCurrentPosition uiRequiredPosition for ctr 700000L ctr ctr while 0
7. co FUJITSU interfacing 4 lepper Motor to the MBaOfado Microcontroller Fujitsu Microelectronics Inc Application Note Contents VNC WEL ONL a raiesy aascaasios rian A E gis stad Lancia E ATE 4 Orientation on Stepper MOtOTS cccccccsseescceseceeeesceessecseecsseseeceeeceseecsaecesecsaecaeeeeesenecssecsaecnscseeseeecsaeeaaenseeeeseseeeaeeeaeeaaees 4 Driving Scheme for a Bipolar Stepper MOtor cccccsccssccessesscecscessecssecsscessceseecssccasesscesscesecessccseceasecsssesscessseseeesseeseceaeees 5 Stepper Motor Control Block on the MB90F598 Microcontroller ccccceccsseessesceeecesceseeeeceeeesecscesceesesecaeesecseeseeseeeeseaeenes 6 Register Details for the Stepper Motor Control Hardware Block c cccccccseesccesesseeseeeseeecesecseesecesecnecaaeeseesesseeeseesecseseeseesaes 8 Description Of Firmware ra i aa a lets vssdavleatseleCoshan a Gates bakaS a aa i e A a Tes 10 Required Items for Running the Sample Code and Demo ccccccccsscessecsecesecesseesscesseeseecssecsscsecesseesecessesaecsseceseeeseecseenaes 13 Connecting a Stepper Motor to the FLASH CAN2 Board with an MB90F598 ccccccccssccssccsecessecsscessceesecssecsseeseceseceseeeses 14 References since isch Gist e enue spond a a a revi aca ctu alee es aaa a a chit dae tbs oi nade Taz te Tope To 15 Fujitsu Microelectronics Inc 3 Interfacing a Stepper Motor to the MBSOFHSS Microcontroller Introduction Stepper motors are w
8. ectors make it easy to connect stepper motors to the board for control by the MB90F598 For more details refer to the user manual for the evaluation board To connect a stepper motor to the first stepper motor controller pins 1 Connect Pins 53 and 58 to DVSS and DVCC respectively A high current input source is required to provide the drive current to the motors see Table 1 2 Connect Pins 54 55 56 and 57 across the two coils of the two coil stepper motor see Table 1 Make these connections accu rately Wrong connections here may produce extreme vibrations and possibly cause physical damage to the motor The complete instructions for downloading and running the demo application are 1 Run FLASHPRG EXE to unzip contents into c fetool by default 2 Execute c fetool flash FLASH361 EXE 3 Set up the options in FLASH361 EXE to address the correct COM ports and speed Also set the CPU to display MB90F598 as shown in the figure below MEE with Flash Memory Writer Witte Weriy aia Information 4 Select the included mhx file by clicking Search in the FLASH361 EXE utility In this case set it as DEMO MHX from the attachment 5 Connect a serial cable from the PC or laptop to the FLASH CAN2 board 6 Change the switches on the board to show 1 5 7 8 ON and the rest OFF allow the FLASH to be programmed 7 Connect a power supply to the FLASH CAN2 board Note the polarities s
9. he current PWM cycle The BS bit is reset to 0 automatically at the beginning of the next PWM cycle If the BS bit is set to 1 by software at the same time as this automatic reset the BS bit is set to 1 or remains unchanged but the automatic reset is cancelled bits 13 to 11 P2 to PO Output Select bits These bits select the output signal at PWM2P0 bits 10 to 8 M2 to MO Output Select bits These bits select the output signal at PWM2M0 bits 5 to 3 P2 to PO Output Select bits These bits select the output signal at PWM1P0 bits 2 to 0 M2 to MO Output Select bits These bits select the output signal at PWM1M0 Table 3 shows the relationship between output levels and select bits Table 3 Output Select Bits P2 P1 PO PWMnPO 0 0 0 L 0 0 1 H 0 1 X PWM pulses 1 X X High impedance M2 M1 M0 PWMnM0 0 0 0 L 0 0 1 H 0 1 X PWM pulses 1 X X High impedance Description of Firmware The following describes software control for the physical movement of the stepper motor rotor using parameters local to the software application 10 Fujitsu Microelectronics Inc Varying the step size of the output signals controls the speed of the stepper motor Different step sizes can be programmed by loading different values into the compare registers Care should be taken to slow the rotor down before the desired position is reached This is demonstrated in the source code The application is set up so th
10. hown in the manual accompanying the board 8 Click Download on the FLASH 361 EXE dialog box 9 Once the download is complete click Auto to program the FLASH 10 Once the preceding steps are successful turn off the power to the board and change the switches to show 3 ON and the rest OFE 11 Connect the stepper motor as shown in Figure 8 14 Fujitsu Microelectronics Inc Application Note MB90F598 FLASH CAN 2 Board Serial Cable Figure 8 Connection Diagram 12 Move the motor pointer to the leftmost position and supply power to the board The motor shaft and the needle will rotate clock wise and stop for a couple of seconds at approximately 60 degrees towards the right hand side it will then rotate counterclockwise to the left hand home position and stop for a couple of seconds The motion will then repeat References The following documents can be found on the Fujitsu MICROS CDROM Version 3 0 or later 1 MB90F598 Data Sheet 2 MB90F598 Hardware Manual 3 FLASH CAN2 Board Manual Fujitsu Microelectronics Inc 15 FUJITSU MICROELECTRONICS AMERICA INC Corporate Headquarters 1250 East Arques Avenue Sunnyvale California 94088 3470 Tel 800 866 8608 Fax 408 737 5999 E mail inquiry fma fujitsu com Internet http Avww fma fujitsu com
11. idely used in printers automated machine tools disk drives automotive dashboard instrument clusters and other applications requiring precise motions using computer control Special logic and high current drive circuits are required to drive stepper motors These can be designed using discrete logic or special interface ICs which may result in either increased design complexity or increased end product cost or both To simplify the design effort and reduce the cost of end products that use stepper motors Fujitsu offers low cost 8 16 and 32 bit microcontrollers with integrated stepper motor drive circuits A common use for stepper motors is in automotive dashboard instrument clusters Stepper motors are used to power the needles or pointers that indicate parameters such as vehicle speed or the RPM of the engine In this application the four stepper motor controllers on Fujitsu MB90F598 Flash Microcontroller can be individually programmed to control the speed gauge the tachometer the fuel gauge and the engine temperature gauge After an introduction to stepper motors and the motor driving schemes this document describes the function of one stepper motor controller on a 16 bit MB90F598 microcontroller The interfaces to the other three stepper motor control macros on the MB90F598 are exactly the same as the one described To demonstrate the working principles of stepper motor interface and control this application note uses
12. r depends on the geometry of the motor rotor Some applications have the flexibility of using either stepper motors or servomotors Although both types of motors offer similar opportunities for precise positioning they differ in a number of ways Servomotors require analog feedback control systems Typically this involves a potentiometer to provide feedback about the rotor position and circuitry to drive a current through the motor The current is inversely proportional to the difference between the desired position and the current position Stepper motors can be used in simple open loop control systems They are generally adequate for systems that operate at low accelerations with static loads Types of Stepper Motors Stepper motors come in two varieties permanent magnet and variable reluctance The reader may be familiar with hybrid motors which are indistinguishable from permanent magnet motors from the controller s point of view Permanent magnet motors usually have two independent windings with or without center taps Center tapped windings are used in unipolar permanent magnet motors see Figure 1 Figure 1 Unipolar Permanent Magnet Motors Bipolar permanent magnet and hybrid motors are constructed with a mechanism similar to that used in unipolar motors except that the two windings are wired without center taps see Figure 2 The motor itself is simpler but the drive circuitry needed to reverse the polarity of e
13. rotation of the motor A synchronization mechanism ensures the synchronous operations of the two PWMs 6 Fujitsu Microelectronics Inc DVSS Function Output for Stepper Motor Controller Channel 0 Output for Stepper Motor Controller Channel 1 Output for Stepper Motor Controller Channel 2 Output for Stepper Motor Controller Channel 3 Dedicated power supply pins for the high current output buffers Pin Nos 54 to 72 Dedicated ground pins for the high current output buffers Pin Nos 54 to 72 Notes CMOS high current output Hysteresis input High Current HYS Figure 5 Circuit for the High Current Output Pins Machine Clock Output Enable PWM1P0 Selector PWM1M0 0E2 Output Enable PWM2P0 PWM2M0 PWM2 Compare Register PWM2 Select Register Figure 6 Block Diagram of the Stepper Motor Hardware Macro Fujitsu Microelectronics Inc 7 Interfacing a olepper Motor to the MBSOFHSS Microcontroller Register Details for the Stepper Motor Control Hardware Block 1 PWM Control 0 Register PWM Control 0 Register Address 00005Eh i 6 5 4 3 2 1 0 lt BitNumber oct Pi po ce tet Pwe Read Write c gt R W R W RAW RW RW RM Initial Valuec gt 0 02 0O 0 o bit 7 OE2 Output enable bit When this bit is set to 1 the external pins are assigned as PWM2P0 and PWM2M0 outputs Otherwise the pins can be used a
14. s general purpose I O bit 6 OE1 Output enable bit When this bit is set to 1 the external pins are assigned as PWM1 PO and PWM1M0 outputs Otherwise the pins can be used as general purpose I O bits 5 to 4 P1 to PO Operation clock select bits These bits specify the clock input signal for the PWM pulse generators Table 2 Operation Clock Select Bits P1 PO Clock Input 0 0 Machine clock 0 1 1 2 machine clock 1 0 1 4 machine clock 1 1 1 8 machine clock bit 3 CE Count enable bit This bit enables the operation of the PWM pulse generators When it is set to 1 the PWM pulse generators start their operation Note that the PWM2 pulse generator starts the operation one machine clock cycle after the PWM1 pulse generator is started This is to help reduce the switching noise from the output drivers 8 Fujitsu Microelectronics Inc bit 0 TST Test bit This bit is for the device test In user applications it should always be set to 0 2 PWM 1 and 2 Compare Registers PWM1 Compare 0 Register Address 000070h T 0 lt BitNumber 6 5 4 3 2 1 05 oe 0s 02 oF pcio Read Write c gt R W RAV RAW RW RW RW R W R W Initial Value gt X X X X X X X X PWM2 Compare 0 Register Address 000071h i5 14 13 11 10 9 8 lt Bit Number 12 Por os o os oe ory oo a Read Write gt R W R W R W RW R W R W R W R W Initial Value gt X X X X X X
15. teps per quadrant CompareRegister_1 LookupTable TableIn dex Jig CompareRegister_2 LookupTable 32 TableIndex l SelectRegister PWS QI 1 st Quadrant means coil_1 is Pos and coil 2 is Pos See Table 4 and 5 The maximum speed that a stepper motor can attain is determined by the physical properties of the motor The motor speed is controlled by varying the step size that is by varying the duty cycle in the compare registers Larger step values make the rotor travel faster and farther The value of the compare registers needs to be controlled carefully to bring the speed of the motor down smoothly when the desired position is being approached Thus the offset that the rotor is allowed to move from the current position towards the required position controls the speed The offset to be added or subtracted from the current offset is a function of the difference between the current position and the required position 12 Fujitsu Microelectronics Inc For the motor to achieve a desired speed a condition such as the following needs to be employed If RequiredPosition_0 CurrentPosition_0 gt CurrentOffset_0 We can speed up the motor CurrentOffset CurrentPosition_0 CurrentPosition_0 CurrentOff set ProgramCompareAndSelectRegisters Similarly when the required position is being reached or when the maximum offset is being reached the speed needs to be reduced and consequently
16. the CurrentOffset needs to be decreased The motion of the rotor can be set in both clockwise and counterclockwise directions The appropriate checks need to be in place for the rotor to correctly turn Check position Has the required position Check speed Can speed be increased Is speed less than maximum speed allowed Is speed more than the offset between the current position and the required position Increase speed by 1 Is speed greater than 1 Select which quadrant of the motor we are dealing with Select duty cycles for the two coils e Set the polarities for the coils Update Figure 7 Program Flow Chart Required Items for Running the Sample Code and Demo FLASH CAN2 Board Part No FLASHCAN2 100MP M06 MB90F598 Microcontroller included in the evaluation kit Stepper motor Connecting wires Serial cable PC or laptop running SOFTUNE V3 0 Application code Flash download utility also on CDROM called FLASH361 EXE Power supply for the FLASH CAN2 Board and also for providing high current inputs required for driving the stepper motor Oo ANN NN BWW Fujitsu Microelectronics Inc 13 Interfacing a Stepper Motor to the MBSOFHSS Microcontroller Connecting a Stepper Motor to the FLASH CAN2 Board with an MB90F598 The FLASH CAN2 evaluation board makes all the MB90F 598 pins accessible through four rows of external connectors These external conn
17. tly Figure 3 shows the control sequences for single stepping such a motor Index 1a 1b 2a 2b S 1 yz A 2 E 1a 0 OOH 0 1b v E g 4 2a o QQQ o 2b S 5 6 E 7 am 8 Figure 3 Control Sequences for Half Stepping a Bipolar Stepper Motor Fujitsu Microelectronics Inc 5 Interfacing a Stepper Motor to the MBSOFHSS Microcontroller Figure 4 shows the control sequences for half stepping such a Table 1 Pin Assignments motor Pin No Pin Name PWM1PO Index 1a 1b 2a 2b PWMIMO 3 2al 54 to 57 PWM2P0 4 PWM2M0 z 4 eto E 59 to 62 PWMP i s 1 1 EIE PWM2M1 7 l l l PWM1P2 8 PWM1M2 9 BE 64 to 67 PWM2P 10 ERER PWM2M2 11 ey PWM1P3 12 aa PWM1M3 3 EA 69 to 72 PWM2P3 14 PWM2M3 if E 16 58 68 DVCC Half Step Sequence Figure 4 Control Sequences for Half Stepping Bipolar Stepper Motors 39u03 Stepper Motor Control Block on the MB90F598 Microcontroller Thestepper motor control block consists of four motor drivers the selector logic and two PWM pulse generators The four motor drivers have high current drive capabilities and they can be directly connected to the four ends of two motor coils The combination of the PWM pulse generators and selector logic controls the
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