Silicon Gate MOS 8255

PROGRAMMABLE PERIPHERAL INTERFACE

24 Programmable I/O Pins

Completely TTL Compatible

Fully Comp.atible with MCS™-8 and MCSTM'_80Microprocessor Families

Direct Bit Set/Reset Capability Easing Control Application Interface

40 Pin Dual In-Line Package

Reduces System Package Count

The 8255 is a general purpose programmable I/O device designed for use with both the 8008 and 8080 microprocessors. It has 24 I/O pins which may be individually programmed in two groups of twelve and used in three major modes of operation. In the first mode (Mode 0), each group of twelve I/O pins may be programmed in sets of 4 to be input or output. In Mode 1, the second mode, each group may be programmed to have 8 lines of input or output. Of the remaining four pins three are used for handshaking and interrupt control signals. The third mode of operation (Mode 2) is a Bidirectional Bus mode which uses 8 lines for a bidirectional bus, and five lines, borrowing one from the other group, for handshaking.

Other features of the 8255 include bit set and reset capability and the ability to source 1mA of current at

1.5volts. This allows darlington transistors to be directly driven for applications such as printers and high voltage displays.

PIN CONFIGURATION

 

8255 BLOCK DIAGRAM

PA3

1

 

 

 

 

 

PA2

2

 

39

PA5

 

 

PAl

3

 

38

PA6

S~~~lEI~S 1--+SV

 

PAO

4

 

37

PA7

 

AD

5

 

36

WR

-- GND

1'0

cs

 

 

 

 

 

1'\ . , .... --- . / PA7·PAO

G

 

35

RESET

 

 

GNO

7

 

34

DO

 

 

Al

8

 

33

0 1

 

 

AO

9

 

32

O2

 

 

PC7

10

8255

31

0 3

 

 

PCG

11

30

0 4

 

1'0

 

 

PC5

12

 

29

Os

 

1'\ ..... ----- . / PCrPC4

 

 

 

 

 

 

 

 

 

PC4

13

 

28

0 6

BI·DIRECTIONAlDATA BUS

 

 

 

 

 

PCO

14

 

27

~

 

 

PCl

15

 

26

V

 

 

 

 

 

 

CC

 

 

PC2

16

 

25

PB7

 

I/~-~ 1'0

PC3

17

 

24

PB6

 

1'\ ...... -- . -.... / PC3·PCO

 

 

 

PBO

18

 

23

PB5

 

 

PB1

19

 

22

PB4

 

 

PB2

20

 

21

PB3

 

 

iffi0

WR --- 0 :~~~~

PIN NAMES

A,

I C~~~~~L

. /'

-- ""

,

1/0

 

 

1'\

-- . -

/

PBrPBo

Ao --- I

0 7 -00

 

RESET --- I

DATA BUS (BI-DIRECTIONAL)

 

RESET

RESET INPUT

 

CS

CHIP SELECT

 

RD

READ INPUT

cs ------ '

WR

WRITE INPUT

 

AO,A1

PORT ADDRESS

 

PA7·PAO.

PORT A (BIT)

 

PB7·PBO

PORT B (BIT)

 

PC7·PCO

PORT C (BIT)

 

VCC

+5 VOLTS

 

GND

gVOLTS

 

5-113

Page 181
Image 181
Intel 8080 manual Programmable Peripheral Interface, ~~~lEI~S 1-- +SV

8080 specifications

The Intel 8085 and 8080 microprocessors were groundbreaking innovations in the world of computing, paving the way for future microprocessor development and personal computing.

The Intel 8080, introduced in 1974, was an 8-bit microprocessor that played a fundamental role in the early days of personal computing. With a 16-bit address bus, it had the capability to address 64 KB of memory. Running at clock speeds of 2 MHz, the 8080 was notable for its instruction set, which included 78 instructions and 246 opcodes. It supported a range of addressing modes including direct, indirect, and register addressing. The 8080 was compatible with a variety of peripherals and played a crucial role in the development of many early computers.

The microprocessor's architecture was based on a simple and efficient design, making it accessible for hobbyists and engineers alike. It included an 8-bit accumulator, which allowed for data manipulation and storage during processing. Additionally, the 8080 featured registers like the program counter and stack pointer, which facilitated program flow control and data management. Its ability to handle interrupts also made it suitable for multitasking applications.

The Intel 8085, introduced in 1976, was an enhancement of the 8080 microprocessor. It maintained a similar architecture but included several key improvements. Notably, the 8085 had a built-in clock oscillator, simplifying system design by eliminating the need for external clock circuitry. It also featured a 5-bit control signal for status line management, which allowed for more flexible interfacing with peripheral devices. The 8085 was capable of running at speeds of up to 3 MHz and had an extended instruction set with 74 instructions.

One of the standout features of the 8085 was its support for 5 extra instructions for stack manipulation and I/O operations, which optimized the programming process. Additionally, it supported serial communication, making it suitable for interfacing with external devices. Its 16-bit address bus retained the 64 KB memory addressing capability of its predecessor.

Both the 8080 and 8085 microprocessors laid the groundwork for more advanced microprocessors in the years that followed. They demonstrated the potential of integrated circuits in computing and influenced the design and architecture of subsequent Intel microprocessors. Their legacy endures in the way they revolutionized computing, making technology accessible to a broader audience, and their influence is still felt in the design and architecture of modern microprocessors today.