Unit 3-PROGRAMMABLE PERIPHERAL INTERFACE-ME6702– MECHATRONICS
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This document discusses the programmable peripheral interface 8255 and its applications. It describes the architecture and operating modes of the 8255 including bit set reset mode and I/O modes 0, 1, and 2. It provides examples of interfacing the 8255 to keyboards, LED displays, analog to digital converters, digital to analog converters, temperature sensors, stepper motors, and traffic light systems. Diagrams and flowcharts illustrate the interfacing between these peripheral devices and a microprocessor using the 8255.
Unit 3-PROGRAMMABLE PERIPHERAL INTERFACE-ME6702– MECHATRONICS
- 2. Content • Introduction • Architecture of 8255 • Keyboard interfacing • LED display –interfacing • ADC and DAC interface • Temperature Control • Stepper Motor Control • Traffic Control interface
- 3. Introduction • To communicate with the outside world, microprocessor use peripherals (I/O devices) • Input devices – Keyboards, A/D converters etc., • Output devices – CRT, Printers, LEDs etc., • Peripherals are connected to the microprocessors through electronic circuit known as interfacing circuits.
- 4. Microprocessors unit with I/O devices Input devices (keyboard) Micro processors Output devices (LED) Input peripherals Output peripherals
- 5. • Some of the general purpose interfacing devices – I/O ports – Programmable peripherals interface (PPI) – DMA controllers – Interrupt controller • Some of the special purpose interfacing devices – CRT controller – Keyboard – Display – Floppy Disc controllers
- 6. Peripheral interfacing Chips are used generation of I/O ports • Programmable peripherals interface Inter 8255 (PPI) • Programmable Interrupt controller (PIC) Intel 8259 • Programmable communication interface (PCI) Intel 8251 • Keyboard display Controller Intel 8279 • Programmable counter /Inverter timer Intel 8253 • A/D and D/A Converter Interfacing
- 7. Microprocessors unit with I/O devices Input devices (key board) PPI 8255 Micro proce ssors 8279 Display Output device (LED) Peripheral Interface Display Interface
- 8. Address Space Partitioning • The Microprocessors uses 16 bit wide address bus for addressing memories and I/O devices. • Using 16 bit wide address bus, it can access 216 = 64k bytes of memory and I/O devices • Two schemes for the allocation of addresses to memories and I/O devices – Memory mapped I/O – I/O mapped I/O
- 9. Memory mapped I/O • It has only one address space • Address space is defined as the set of all possible addresses that a microprocessor can generate • Some addresses assigned to memories and Some addresses to I/O devices • Memory locations are assigned with addresses from 8000 to 84FF • I/O devices are assigned with addresses from 8500 to 85FF
- 10. I/O mapped I/O scheme • In this scheme, addresses assigned to memories locations can also be assigned to I/O devices • Since the same address may be assigned to memories locations or an I/O devices • The microprocessor has a signal to distinguish whether the address on the address bus is for memories locations or an I/O devices
- 11. I/O mapped I/O scheme • When signal is high, then address on the address bus is for an I/O devices • When signal is low, then address on the address bus is for memory locations • Two extra instruction IN and OUT are used to address I/O devices. • The IN instruction is used to read the data of an input devices. • The OUT instruction is used to send the data of an input devices. • This scheme is suitable for a large system.
- 12. PROGRAMMABLE PERIPHERALS INTERFACE INTER 8255 (PPI)
- 13. Operating mode of 8255 • Bit Set Reset (BSR) Mode • I/O Mode
- 14. Bit Set Reset (BSR) Mode BSR control word format
- 15. I/O Mode • The 8255 has the following 3 modes of operation – Mode 0 – Simple Input/output – Mode 1 – Input / Output with the Handshake or strobed – Mode 2 – Bi-directional I/O
- 16. I/O Mode Mode 0 – Simple Input/output – Port A and port B are used as two simple 8-bit I/O port – Port C as two 4-bit port • Features – Outputs are latched – Inputs are buffered not latched – Ports do not have handshake or interrupt capability
- 17. I/O Mode • Mode 1 – Input / Output with the Handshake – Input or output data transfer is controlled by handshaking signals. – Handshaking signals are used to transfer data between devices whose data transfer speeds are not same. – Port A and Port B are designed to operate with the Port C. – When Port A and Port B are programmed in Mode 1, 6 pins of port C is used for their control.
- 18. I/O Mode • D0-D7 data bus – bi directional, tri state data bus line – It is used to transfer data and control word from 8085 to 8255 • RD (Read) – When this pin is low, the CPU can read data in the port or status word through the data buffer • WR (write) – When this pin is low, the CPU can write data in the port or in the control register through the data buffer
- 19. I/O Mode • Mode 2 – Bi-directional I/O • Port A can be programmed to operate as a bidirectional port. • The mode 2 operation is only for port A • When port A is programmed in Mode 2, the Port B can be used in either Mode 1 or Mode 0. • Mode 2 operation the port a is controlled by PC3 to PC7 of port C.
- 22. PROGRAMMING and OPERATION of 8255 • Programming in MODE 0 • D7 –set to 1 • D6,D5,D2- all set to 0 –MODE 0 • D4,D3,D1 and D0- determine weather the corresponding ports are to configured as input or output
- 23. A B GROUP A GROUP B D4 D3 D1 D0 PORT A PORTC U PORT B PORT C L 0 0 0 0 OUT OUT OUT OUT 0 0 0 1 OUT OUT OUT IP 0 0 1 0 OUT OUT IP OUT 0 0 1 1 OUT OUT IP IP 0 1 0 0 OUT IP OUT OUT 0 1 0 1 OUT IP OUT IP 0 1 1 0 OUT IP IP OUT 0 1 1 1 OUT IP IP IP 1 0 0 0 IP OUT OUT OUT 1 0 0 1 IP OUT OUT IP 1 0 1 0 IP OUT IP OUT 1 0 1 1 IP OUT IP IP 1 1 0 0 IP IP OUT OUT 1 1 0 1 IP IP OUT IP 1 1 1 0 IP IP IP OUT 1 1 1 1 IP IP IP IP
- 24. Programming in MODE 1
- 25. • IBF- input buffer full • INTR- interrupt request • INTE-interrupt enable • OBF-output buffer full • INTR-interrupt request • INTE-interrupt enable
- 26. Programming in MODE 2
- 31. 2 X 2 Key operation
- 32. Keyboard Microprocessor Interface software Flowchart
- 36. LED Operation
- 38. Microprocessor interface to LED (Common anode)
- 40. Microprocessor interface to 7 segment LED (Parallel)
- 41. Microprocessor interface to 7 segment LED (serial)
- 42. Serial interface of 7 segment LED to Microprocessor software flowchart
- 45. ADC INTERFACE
- 46. BLOCK diagram of ADC 0808
- 48. PIN diagram of ADC 0808
- 49. DAC INTERFACE
- 50. Pin diagram of DAC
- 51. Pin diagram of DAC
- 52. INTERFACING diagram for DAC
- 53. TEMPERATURE CONTROL • Temperature sensor –convert temp to electrical signal by thermistor • Transducer convert physical data into electrical signal • Physical data –temp, light, flow, speed etc… • LM34 & LM35 –temperature sensor by NATIONAL SEMICONDUCTOR CO-OPERATION
- 54. • LM34 • Output voltage is linearly proportional to Fahrenheit temp • No external calibration • 10mV for each degree of Fahrenheit temp • LM35 • Output voltage is linearly proportional to Celsius temp • No external calibration • 10mV for each degree of Centigrate temp
- 56. STEPPER MOTOR CONTROL interface • Digital motor used to translate electrical pulse into mechanical movement • Center tap winding connected to 12 V supply • Motor can be excited by grounding four terminals of the two windings • ROTOR-Stepper motor has permanent magnet rotor .It is also known as shaft • STEP ANGLE-It is minimum degree of rotation associated with a single step
- 59. Excitation Table Step X1 X2 X3 X4 1 0 1 0 1 2 1 0 0 1 3 1 0 1 0 4 0 1 1 0 1 0 1 0 1
- 60. Traffic Light Control System • Allow traffic from W to E and E to W transition for 20 seconds • Give transition period of 5 seconds (yellow bulbs ON) • Allow traffic from N to s and S to n for 20 seconds • Give transition period of 5 seconds (yellow bulbs ON) • Repeat the process
- 61. Traffic Light Control System
- 62. Interfacing diagram for Traffic Light Control System