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
– 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 low, 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
39. • INPUT CONTROL SIGNAL:
– STB
• Low input signal enables PORT A
– IBF
• High input devices indicates loaded loaded on port a
– INTE2
• 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
66. 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
67. • 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
68.
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
73. 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