The 8255 Programmable Peripheral Interface (PPI) allows a microprocessor to interface with external devices by providing three 8-bit I/O ports (Ports A, B, and C). It can operate in different modes to control the direction and functionality of the ports. The document describes the features and pinout of the 8255, its operation modes including Mode 0 for simple I/O, and provides an example of interfacing it with an 8085 microprocessor.

1. 8255
Programmable Peripheral
Interface
Prepared by:
ABHIMANYU JHA
STEPHEN SAMUEL
MOHD. HAMZA
Presentation on

2. 8255 Programmable peripheral
Interface:
 PPI 8255 is a general purpose programmable I/O device
designed to interface the CPU with its outside world such as
ADC, DAC, keyboard etc.
 It can be used with almost any microprocessor.
 It consists of three 8-bit bidirectional I/O ports i.e. PORT A,
PORT B and PORT C.

3. PROGRAMMABLE PERIPHERAL
INTERFACE -8255
Features:
 It is a programmable device.
 It has 24 I/O programmable pins like PA,PB,PC (3-8 pins).
• TT L compatible.
• Improved dc driving capability

4. Features:(contd.)
 It has three separately accessible ports.
 The individual ports of the 8255 can be
programmed to be input or output, and can
be changed dynamically

5. Pin diagram of 8255

6. P A 3
P A 2
P A 1
P A 0
R D
C S
G N D
A 1
A 0
P C 7
P C 6
P C 5
P C 4
P C 0
P C 1
P C 2
P C 3
P B 0
P B 1
P B 2
P B 4
P B 5
P B 6
P B 7
W R
R E S E T
D 0
D 1
D 2
D 3
D 4
D 5
D 6
D 7
V C C
P B 7
P B 6
P B 5
P B 4
P B 3
1
3
2
4
5
6
7
3
3
9
8
1 0
1 2
1 3
1 1
1 4
1 5
1 6
1 7
1 9
2 0
1 8
4 0
3 9
3 8
3 7
3 6
3 5
3 4
3 3
3 2
3 1
3 0
2 9
2 8
2 7
2 6
2 5
2 4
2 3
2 2
2 1
8 2 5 5 A
Pin diagram 8255

7. Function of pins:
 Data bus(D0-D7):These are 8-bit bi-directional buses,
connected to 8085 data bus for transferring data.
 CS:This is Active Low signal.When it is low, then data is
transfer from 8085.
 Read:This is Active Low signal, when it is Low read
operation will be start.
 Write:This is Active Low signal, when it is LowWrite
operation will be start.

8. A1 A0 Select
0 0 PA
0 1 PB
1 0 PC
1 1
Control
reg.
 Address (A0-A1):This is used to select the
ports. like this

9.  RESET:This is used to reset the device.That means clear
control registers.
 PA0-PA7:It is the 8-bit bi-directional I/O pins used to send
the data to peripheral or
or to receive the data from peripheral.
 PB0-PB7:Similar to PA
 PC0-PC7:This is also 8-bit bidirectional I/O pins.These
lines are divided into two groups.
1. PC0 to PC3(Lower Groups)
2. PC4 to PC7 (Higher groups)
These two groups working in separately using 4 data’s.

10. P o w e r
S u p p lie s
+ 5 V
G N D
G ro u p
A
c o n tro l
8 2 5 5 B lo c k D ia g ra m
G ro u p
A
p ro t
A
( 8 )
G ro u p
A
p ro t C
U p p e r
( 4 )
G ro u p
A
p ro t C
L o w e r
( 4 )
G ro u p
B
p ro t
B
( 8 )
G ro u p
B
c o n tro l
R e a d /
w rite
c o n tro l
lo g ic
D a ta
b u s
b u f fe r 8 - b it
I n te rn a l
d a ta b u s
B id ire c tio n a l
D a ta B u s
D 7 - D 0
R D
W R
A 1
A 0
R E S E T
C S
I O
P B 7 - P B 0
I O
P C 3 - P C 0
I O
P C 7 - P C 4
I O
P A 7 - P A 0

11. PA, PB, PC
(Port
A,B,C)
8 bit i/o ports
CS (Chip Select) A low signal at this pin enables the
chipRD (Read) Read enable
WR (Write) Write enable
D0-D7 (Data
Bus)
Bi-directional data lines
A0,A1 (Address) Address select
Pin description

12. Interfacing Of 8255
with other microprocessor
e.g. (8085 or 8086)

13. A
B
Y 0
G 2 A
G 1
C
G 2 B
Y 1
Y 2
Y 3
Y 4
Y 5
Y 6
Y 7
A 7
A 3
A 4
A 6
A 5
A 0
D 7 - D 0
I O R C
I O W C
A 1
A 2
R E S E T
R D
W R
A 0
A 1
R E S E T
C S
D 0
D 1
D 2
D 3
D 4
D 5
D 6
D 7
P A 0
P A 1
P A 2
P A 3
P A 4
P A 5
P A 6
P A 7
P B 0
P B 1
P B 2
P B 3
P B 4
P B 5
P B 6
P B 7
P C 0
P C 1
P C 2
P C 3
P C 4
P C 5
P C 6
P C 7
PortCPortBPortA

14. Control Bytes for I/O mode
1
D0D1D2D3D4D5D6D7
Group B
Port C (lower)
1 = input
0 = output
Port B
1 = input
0 = output
Mode selection
00 = mode 0
01 = mode 1
1x = mode 2
Group A
Port C (upper)
1 = input
0 = output
Port A
1 = input
0 = output
Mode selection
00 = mode 0
01 = mode 1
1x = mode 2

15. Modes Of Operation
The 8255 can work in 2 modes that are I/O
mode and BSR mode
i/o mode is further divided in to
1. Mode 0 (Basic I/O)
2. Mode 1 (Strobe I/O)
3. Mode 2 (Bi - Conditional Bus)

16. Operation modes:
BIT SET/RESET MODE:
The PORT C can be Set or Reset by sending OUT
instruction to the CONTROL registers.
I/O MODES:
MODE 0 (Simple input / Output):
In this mode , port A, port B and port C is used as
individually (Simply).
Features:
Outputs are latched , Inputs are buffered not latched.
Ports do not have Handshake or interrupt capability.

17. MODE 0: simple i/p and o/p
 In this mode all the three ports (port A, B, C) can work as
simple input function or simple output function
 . In this mode there is no interrupt handling capacity.
 Port A and Port B can be configured as simple 8-bit input
or output ports without handshaking.
 The two halves of Port C can be programmed separately
as 4-bit input or output ports.
 In this mode, any of the ports A, B, CL, and CU can
be programmed as input or output.

18. ThankYou