SILICON GATE MOS 8255

APPLICATIONS OF THE 8255

The 8255 is a very powerful tool for interfacing peripheral equipment to the 8080 microcomputer system. It represents the optimum use of available pins and is flexible enough to interface almost any I/O device without the need for ad- ditional external logic.

Each peripheral device in a Microcomputer system usually has a "service routine" associated with it. The routine man- ages the software interface between the device and the CPU. The functional definition of the 8255 is programmed by the I/O service routine and becomes an extension of the sys- tems software. By examining the I/O devices interface char- acteristics for both data transfer and tim ing, and matching this information to the examples and tables in the Detailed Operational Description, a control word can easily be de- veloped to initialize the 8255 to exactly "fit" the applica- tion. Here are a few examples of typical applications of the 8255.

INTERRUPT

REQUEST

 

HIGH-SPEED

 

PRINTER

MODEl

 

(OUTPUT)

 

 

HAMMER

 

RELAYS

 

DATA READY

 

ACK

 

PAPER FEED

 

FORWARD/REV

8255

 

 

DATA READY

 

ACK

MODEl

PAPER FEED

(OUTPUT)

FORWARD/REV

 

 

RIBBON

 

CARRIAGE SEN.

PC,

DATA READY

PC2

ACK

CONTROL LOGIC AND DRIVERS

INTERRUPT

REQUEST

Printer Interface

INTERRUPT

REQUESTi

PC3

-

Ro

 

PAo

 

 

 

8255

PA,

R,

 

 

PA2

R2

FULLY

 

PA3

R3

DECODED

 

KEYBOARD

 

PA4

R4

 

MODE 1 _

PAs

Rs

 

PA6

SHIFT

 

(INPUT)

 

 

PA7

CONTROL

 

PC4

STROBE

 

PCs

ACK

 

 

~

 

 

-

 

 

 

PBo

Bo

 

 

 

 

 

 

PB,

B,

 

 

 

 

 

 

PB2

B2

BURROUGHS

 

 

 

 

SELF·SCAN

 

 

 

 

PB3

B3

 

DISPLAY

 

 

 

 

PB4

B4

 

 

 

MODE 1 _

PBs

Bs

 

 

 

PB6

BACKSPACE

 

(OUTPUT)

 

 

 

 

PB7

CLEAR

 

 

 

 

 

PC,

DATA READY

 

 

 

 

PC2

ACK

 

 

 

 

 

PC6

BLANKING

 

 

 

PCo

L.fC7

CANCEL WORD

 

INTERR UPT~

 

 

 

 

 

REQUEST

 

 

 

 

 

 

 

Keyboard and Display Interface

 

 

 

 

REQUESTi

 

 

 

 

 

 

 

INTERRUPT

 

 

 

 

 

 

 

PC3

PAo

Ro

 

 

 

 

 

 

 

 

 

 

PA,

R,

 

 

 

 

 

PA2

R2

 

 

 

MODE 1

 

PA3

R3

FULLY

 

 

DECODED

 

(INPUT) -

PA4

R4

KEYBOARD

 

 

 

 

 

 

 

 

PAs

Rs

 

 

 

8255

 

I PA6

SHIFT

 

 

 

 

PA7

 

 

 

 

 

 

CONTROL

 

 

 

 

PC4

STROBE

 

 

 

 

PC s

ACKNOWLEDGE

 

 

 

PC6

BUSY LT

 

 

 

 

PC7

TEST LT

 

 

f-------_--

 

--

 

 

 

 

PB o

....

'0

TERMINAL

 

 

PB,

....

--

~

ADDRESS

 

 

PB2

 

--

't>

 

MODE 0

 

PB3

....

--"0

 

(INPUT)

-

PB4

 

-- ....

 

 

 

 

 

 

 

PBs

 

-- "",

 

 

 

.... --

 

 

 

 

PB6

 

 

 

 

PB7

....

--

 

 

~

Keyboard and Terminal Address Interface

5-127

Page 195
Image 195
Intel 8080 manual Applications, Printer Interface, Keyboard and Display Interface, Keyboard and Terminal Address Interface

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.