Term Programmable Peripheral Interface (PPI) is used for the integrated circuits that interface / connect the external world to the central processing unit (CPU). Generally, a variety of programming modes are provided with the IC.

8255A is a general purpose programmable peripheral interface I/ O device for Intel microprocessor. It has twenty-four I/ O pins which can be individually programmed in two groups of twelve and can be used in three different modes.

Features of 8255A-5

  • 24 programmable I/O pins
  • Completely TTL compatible
  • Fully compatible with intel microprocessor families
  • Improved timing characteristics
  • Direct bit set/ reset capability
  • Reduce system package count
  • Improve DC driving capability

Replacement Part

MSM82C55A-2

Pictorial View

Pictorial view of the UTsource 8255A-5 is shown below and price can be found; it is a forty pin DIP package

Pin Description

Pin description of the IC 8255A-5 is shown below

Pin Number 

Pin Name 

Description

34 - 27

D0-D7

Data bus

6

/CS

Chipset

35

RESET

Reset 

5

/RD

Read control

36

/WR

Write control

8 – 9

A0-A1

Port address

4 -1, 40 - 37

PA0-PA7

I/ O port A

18 - 25

PB0-PB7

I/ O port B

10 - 17 

PC0-PC7

I/ O port C

7

Gnd

Ground

26 

VCC

Power supply

8255A-5 Electrical Characteristics/ Specifications

Parameter 

Description 

Value

TSTG

Storage temperature 

-65 to 150 C

VPIN

Voltage on any pin

-0.5 to 7 V

PD

Power dissipation

1 W

VIL

Input low voltage

-0.5 to 0.8 V

VIH

Input high voltage

2.0 to VCC

VOL(DB)

Output low voltage on data bus

0.45 V

VOL(PER)

Output low voltage on peripheral bus

0.45 V

VOH(DB)

Output high voltage on data bus

2.4 V

VOH(PER)

Output high voltage on peripheral bus

2.4 V

ICC

Power supply current 

120 mA

IOFL

Output float leakage 

± 10 µA

IL

Input load current

± 10 µA

Working Principle

8255A is a PPI designed to interface microprocessors manufactured by Intel. Its main function is interface general purpose I/ O components with the system bus. The functional configuration of the 8255A is programmed by the system software so that normally no external logic is necessary to interface the peripheral device or structure. A table explaining the basic operation of the 8255A is given below

A0

A1

/WR

/RD

/CS

Input Operation

0

0

1

0

0

Port A to Data Bus

1

0

1

0

0

Port B to Data Bus

0

1

1

0

0

Port C to Data Bus

Output Operation (Write)

0

0

0

1

0

Data Bus to Port A

1

0

0

1

0

Data Bus to Port B

0

1

0

1

0

Data to Port C

1

1

0

1

0

Data Bus to Control

X

X

X

X

1

Data Bus to 3 State

1

1

1

0

0

Illegal Condition

X

X

1

1

0

Data Bus to 3 State

Applications 

General purpose programmable I/O device for Intel Microprocessor

Keyboard and Display Interface

A keyboard and display interface using P8255A is shown in the figure below


Printer Interface

Pinter interface using 8255A PPI is shown below