1. Applications of PPI Stepper Motors- D/A - A/D - Temperature Sensor

2. Stepper Motors More accurately controlled than a normal motor allowing fractional turns or n revolutions to be easily done Lower speed, and lower torque than a comparable D.C. motor useful for precise positioning for robotics Servomotors require a position feedback signal for control

3. Stepper Motor Diagram Rotor Alignment

4. Stepper Motor Step Angles SPR: Steps per Revolution SA: Step Angle (degree) 5000.72 2001.8 1802 1442.5 725 487.5 2415 SPS: Steps per second SPS = (RPM * SPR) /60

5. Stepper Motor Types – Variable Reluctance – Permanent Magnet

6. Variable Reluctance Motors

7. This is usually a four wire motor – the common wire goes to the +ve supply and the windings are stepped through The current example is a 30 o motor The rotor has 4 poles and the stator has 6 poles Example

8. Transient StateStable State 0 30 60 50 25 75 1 4 3 2 5 6

9. Variable Reluctance Motors To rotate we excite the 3 windings in sequence – W1 – 1 0 0 1 0 0 1 0 0 1 0 0 1 001001001001 – W2 – 0 1 0 0 1 0 0 1 0 0 1 0 0 100100100100 – W3 – 0 0 1 0 0 1 0 0 1 0 0 1 0 010010010010 0 30 60 90 120 150 180 210 240 270 300 330 360 30 This gives two full revolutions

10. Unipolar Motors

11. Half Cycle Stepping 105 75 45 150 90 60 30

12. Full Cycle Stepping

13. Unipolar Motors (Full) To rotate we excite the 2 windings in sequence – W1a – 1 0 0 0 1 0 0 0 1 0 0 0 1000100010001 – W1b – 0 0 1 0 0 0 1 0 0 0 1 0 0010001000100 – W2a – 0 1 0 0 0 1 0 0 0 1 0 0 0100010001000 – W2b – 0 0 0 1 0 0 0 1 0 0 0 1 0001000100010 – 0 30 60 90 120 150 180 210 240 270 300 330 360 This gives two full revolutions

14. Basic Actuation Wave Forms

15. Unipolar Motors (Half) The two sequences are not the same, so by combining the two you can produce half stepping – W1a – 1 1 0 0 0 0 0 1 1 1 0000011100000111 – W1b – 0 0 0 1 1 1 0 0 0 0 0111000001110000 – W2a – 0 1 1 1 0 0 0 0 0 1 1100000111000001 – W2b – 0 0 0 0 0 1 1 1 0 0 0001110000011100 – 0 15 30 45 60 75 90 105 120 145 150

16. Enhanced Waveforms (Full) better torque more precise control

17. Unipolar Motors (Enhanced Full) To rotate we excite the 2 windings in sequence – W1a - 1100110011001100110011001 – W1b - 0011001100110011001100110 – W2a - 0110011001100110011001100 – W2b - 1001100110011001100110011 This gives two full revolutions at 1.4 times greater torque but twice the power

18. Motor Control Circuits For low current options the ULN200x family of Darlington Arrays will drive the windings direct.

19. Interfacing to Stepper Motors

20. 8255 Control Word

21. Example (Enhanced Full) Required Sequence: 1100 – 0110 – 0011 - 1001

25. Digital to Analog Converter

26. Example – Step Ramp

27. Analog to Digital

28. V in Range

29. Timing

30. Interfacing ADC

31. Example

32. Temperature Sensor

33. Printer Connection

34. IO Base Address for LPT

35. Printer’s Ports

36. 8255 Mode Definition Summary

37. Mode 0 Provides simple input and output operations for each of the three ports. – No “handshaking” is required, data is simply written to or read from a specified port. – Two 8-bit ports and two 4-bit ports. – Any port can be input or output. – Outputs are latched. – Inputs are not latched

38. Mode 1 Basic functional Definitions: – Two Groups (Group A and Group B). – Each group has one 8-bit data port and one 4-bit control/data port. – The 8-bit data port can be either input or output. Both inputs and outputs are latched. – The 4-bit port is used for control and status of the 8-bit data port.

39. 8255 mode 1 (output)

40. Mode 1 – Control Signals Output Control Signal Definition – OBF (Output Buffer Full F/F). (C7 for A, C1 for B) The OBF output will go “low” to indicate that the CPU has written data out to the specified port. – A signal to the device that there is data to be read. – ACK (Acknowledge Input). (C6 for A, C2 for B) A “low” on this input informs the 8255 that the data from Port A or Port B has been accepted. – A response from the peripheral device indicating that it has read the data. – INTR (Interrupt Request). (C3 for A, C0 for B) A “high” on this output can be used to interrupt the CPU when an output device has accepted data transmitted by the CPU.

41. Timing diagram for mode1(output)

42. 8255 mode 1 (input)

43. Mode 1 – Control Signals Input Control Signal Definition – STB (Strobe Input). (C4 for A, C2 for B) A “low” on this input loads data into the input latch. – IBF (Input Buffer Full F/F) (C5 for A, C1 for B) A “high” on this output indicates that the data has been loaded into the input latch; in essence, an acknowledgement from the 8255 to the device. – INTR (Interrupt Request) (C3 for A, C0 for B) A “high” on this output can be used to interrupt the CPU when an input device is requesting service.

44. Timing diagram for mode1(input)

45. MODE 2 Basic Functional Definitions: – Used in Group A only. – One 8-bit, bi-directional bus port (Port A) and a 5-bit control port (Port C). – Both inputs and outputs are latched. – The 5-bit control port (Port C) is used for control and status for the 8-bit, bi-directional bus port (Port A).

46. Mode 2 Output Operations – OBF (Output Buffer Full). The OBF output will go low to indicate that the CPU has written data out to port A. – ACK (Acknowledge). A low on this input enables the tri-state output buffer of Port A to send out the data. Otherwise, the output buffer will be in the high impedance state. Input Operations – STB (Strobe Input). A low on this input loads data into the input latch. – IBF (Input Buffer Full F/F). A high on this output indicates that data has been loaded into the input latch. PinFunction PC7/OBF PC6/ACK PC5IBF PC4/STB PC3INTR PC2I/O PC1I/O PC0I/O