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. • Each I/O device requires separate interfacing
circuit
• The circuit converts the data in input device in
to compitable format
• Output device converts o/p of microprocessor.
• Some of the interfacing devices are listed below:
– General purpose device
– Special purpose device
6. • Some of the general purpose interfacing devices
– I/O ports
– Programmable peripherals interface (PPI)
– D/A controllers
– Interrupt controller
• Some of the special purpose interfacing devices
– CRT controller
– Keyboard
– Display
– Floppy Disc controllers
7. Peripheral interfacing Chips are used
generation of I/O ports
• Programmable peripherals interface Intel 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
8. Microprocessors unit with I/O devices
Example
Input
devices
(key
board)
PPI
8255
Micro
proce
ssors
8279
Display
Output
device
(LED)
Peripheral
Interface
Display
Interface
9. 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
10. 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 80FF
• I/O devices are assigned with addresses from 8500
to 85FF
11. 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
12. 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.
14. • It is a multi port device.
• Ports can be programmed in variety ways
required by an operator.
• It is a general purpose programmable i/o devices
• It has 24 i/o pins 3*8 bit parallel ports.
• Port A, Port B, Port C,
• Port C can be groped in to two groups as 4 bits
15. FEATURES OF 8255
• 8255 is a widely used , programmable ,
parallel i/o devices
• It can easily transfer data under various
conditions
• Compatible with all micro processors
• Bit reset allows set reset of port C
• 8255 can operate 3 i/o modes
– Mode 0, Mode1 , mode 2
16. BLOCK DIAGRAM OF 8255
• It consists of Two 8 bit ports Port-a port – b, and
two 4 bit ports port C( upper and lower)
• GROUP-AAND GROUP –B CONTROLS:
– Group A control PC7-PC4
– Group B control PC3-PC0
17. • Port A 8 bit latched with three modes MODE
0,1,2
• Port B has 8 bit data input buffer mode 0,1
• Port C Port c 8 bit i/o buffer.
• DATA BUS BUFFER:
– Tri state bi directional buffer used to interface
internal bus data
– Read the data from the buffer/ write the data from
buffer
18. OPERATING MODE OF 8255
• Bit Set Reset (BSR) Mode
• I/O Mode
• BSR MODE:
– Reset the bits in port C
• I/O MODE :
– Mode 0- simple I/O ports
– Mode 1 – I/O ports with handshake
– Mode 2 – Bi directional I/O data transfer
20. I/O Mode
• Mode 0: Simple Input and Output
– Port A,B,C1 and C2 Each 8 bits
– Outputs are latched
– Ports do not have handshake
21. I/O Mode
• MODE 1: INPUT/ OUTPUT WITH
HANDSHAKE
– Input or output data transfer controlled by handshaking
signals
– Hand shaking speed and data transfer speeds are not
same (Ex: printer and system data transfer speed)
– Ports A and B are designed to operate port C
– Port a And Port B are programmed at mode 1
– PINS ARE
• PORT A - PC3, PC4, PC5 output port
• PORT C –PC6, PC7 i/p or o/p
• Port A in Mode 1- Port B is operated in MODE 0
22. 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 high, the CPU can write data in
the port or in the control register through the data
buffer
23. Mode2
• Mode 2 – Bi-directional I/O
• Port A can be programmed to operate as a
bidirectional operation.
• 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.
27. • RESET:
– High input is used to reset 8255.
– Reset input is high control register is cleared
– Reset signal from 8085 is used to reset 8255
• A0 and A1
– Input signals with RD and WR status
• PA0-PA7 (port –a)
– 8 bit bi-directional I/O pins datas send data to output
device and receive data to input device
• PB0-PB7 (Port –B)
– I/O pins datas send data to output device and receive
data to input device
28. PROGRAMMING and
OPERATION of 8255
I) Programming in MODE 0
• A,B,C configured as input and output ports.
• 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
29. 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
30. • INPUT MODE
– After initializing the 8255 input mode 0
– CPU can read through initiate the read command (
example PENDRIVE)
– READ command activates RD signal
31. • OUTPUT MODE:
– After initializing the output mode 0
– CPU can write data in initiating command with
proper port address.
34. • OUTPUT BUFFER FULL
– Output signal goes low when microprocessor unit
writes data in the output latch 8255
– 8255 receives acknowledgement to that peripheral
• ACK (acknowledgement)
– Input peripheral has low output pheripheral devices
has receive data
• INTR AND INTE
– Interrupt request
– Interrupt enable
38. • INPUT CONTROL SIGNAL:
– STB(strobe input)
• Low input signal enables PORT A
– IBF(input buffer full)
• High input devices indicates loaded loaded on port a
– INTE(interrupt request)
• Interrupt enable with input buffer full.
• OUTPUT CONTROL SIGNAL:
– OBF
• Low output indicates cpu written data in port a
– ACK
• Low input signal enables output buffer of port A
47. LED Interface
•Light Emitting diodes are used to display, events
are messages.
•Total number of characteristics is fixed, not like
the CRT displays
•Diodes when conducts current it emits light
energy
49. Microprocessor interface to LED
(Common anode)
•In Common CATHODE configuration whenever
the bit is 1 corresponding LED is glow
•In common ANODE configuration 0 in any bit
position LED will glow.
56. ANALOG TO DIGITAL CONVERTER
• The A/D conversion is a quantizing process an
analog signal in to equivalent binary word.
• ADC family
– The ADC 0808 and 0809 are monolithic CMOS
device with an 8 channel multiplexer
– These devices are designed to operate from the
command to micro processor control bussed with
the tristate latches driving the data bus.
65. TEMPERATURE CONTROL
• Transducer convert physical data into electrical
signal
• Physical data –temp, light, flow, speed etc…
• Depending on the transducer can produce output
such as, VOLTAGE, CURRENT, RESISTANCE.
• Temperature sensor –convert temperature to
electrical signal by thermister.
• LM34 & LM35 –temperature sensor series from
NATIONAL SEMICONDUCTOR CO-
OPERATION
66. • 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
69. 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
70. • The given excitation sequence rotates motor in
clockwise direction
• Excitation sequence changes due to winding
connections
• The table give step excitation sequence
• Each step of the motor is 0.9 degree
74. 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