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UNIT III PROGRAMMABLE PERIPHERAL INTERFACE
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- 2. Content • Introduction • Architectureof 8255 • Keyboard interfacing • LED display –interfacing • ADC and DAC interface • Temperature Control • Stepper Motor Control • Traffic Control interface
- 3. Introduction • To communicatewith 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 withI/O devices Input devices (keyboard) Micro processors Output devices (LED) Input peripherals Output peripherals
- 5. • Some ofthe general purpose interfacing devices – I/O ports – Programmable peripherals interface (PPI) – DMA controllers(Direct memory access) – Interrupt controller • Some of the special purpose interfacing devices – CRT controller – Keyboard – Display – Floppy Disc controllers
- 6. Some peripheral interfacingchips of 8085 and 8086 microprocessors. • 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 withI/O devices Input devices (key board) PPI 8255 Micro proce ssors 8279 Display Output device (LED) Peripheral Interface Display Interface
- 8. Address Space Partitioning •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 • It is suitable for small system.
- 10. I/O mapped I/Oscheme • In this scheme, addresses assigned to memories locations can also be assigned to I/O devices • When the signal is high, then address on the address bus is for an I/O devices • When the signal is low, then address on the address bus is for memory locations.
- 11. I/O mapped I/Oscheme • 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 INTERFACEINTER 8255 (PPI)
- 13. Operating mode of8255 • Bit Set Reset (BSR) Mode • I/O Mode
- 14. Bit Set Reset(BSR) Mode BSR control word format
- 15. I/O Mode • The8255 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 • Mode1 – 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-D7data 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 • Mode2 – 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.
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- 22. PROGRAMMING and OPERATIONof 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 GROUPA 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
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- 25. • IBF- inputbuffer full • INTR- interrupt request • INTE-interrupt enable • OBF-output buffer full • INTR-interrupt request • INTE-interrupt enable
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- 31. 2 X 2Key operation
- 32. Keyboard Microprocessor Interfacesoftware Flowchart
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- 38. Microprocessor interface toLED (Common anode)
- 40. Microprocessor interface to7 segment LED (Parallel)
- 41. Microprocessor interface to7 segment LED (serial)
- 42. Serial interface of7 segment LED to Microprocessor software flowchart
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- 46. BLOCK diagram ofADC 0808
- 48. PIN diagram ofADC 0808
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- 53. TEMPERATURE CONTROL • Temperaturesensor –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 • Outputvoltage 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 CONTROLinterface • 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
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- 59. Excitation Table Step X1X2 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 ControlSystem • 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 ControlSystem
- 62. Interfacing diagram forTraffic Light Control System
- 64. Traffic Light ControlSystem
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