Silicon Gate MOS 8251

PROGRAMMABLE COMMUNICATION INTERFACE

.. Synchronous and Asynchronous Operation

• Synchronous:

5-8 Bit Characters

Internal or External Character

Synchronization

Automatic Sy.nc Insertion

• Asynchronous:

5-8 Bit Characters

Clock Rate -1,16or 64 Times Baud Rate

Break Character Generation 1, 11h, or 2 Stop Bits False Start Bit Detection

•Baud Rate - DC to 56 k Baud ( Sync Mode) DC t09.6k Baud (Async Mode)

•Full Duplex, Double Buffered, Transmitter and Receiver

•Error Detection - Parity, Overrun, and Framing

•Fully Compatible with 8080 CPU

•28-Pin DIP Package

•All Inputs and Outputs Are TTL Compatible

•Single 5 Volt Supply

•Single TTL Clock

The 8251 is a Universal Synchronous/Asynchronous Receiver / Transmitter (USA RT) Chip designed for data communications in microcomputer systems. The USART is used as a peripheral device and is programmed by the CPU to operate using virtually any serial data transmission technique presently in use (including IBM Bi-Sync). The USART accepts data characters from the CPU in parallel format and then converts them into a continuous serial data stream for transmission. Simultaneously it can receive serial data streams and con- vert them into. parallel data characters for the CPU. The USART will signal the CPU whenever it can accept a new character for transmission or whenever it has received a character for the CPU. The CPU can read the complete status of the USART at any time. These include data transmission errors and control signals such as SYNDET, TxEMPT. The chip is constructed using N-channel silicon gate technology.

PIN CONFIGURATION

 

BLOCK DIAGRAM

 

 

 

 

 

O2

0 1

 

 

 

0 3

Do

 

 

 

RxD

Vee

 

 

 

GND

RxC

 

TRANSMIT

TxD

0 4

DTR

0 7 -00

BUFFER

 

(p.... S)

 

05

RTS

 

 

 

0 6

DSR

 

 

 

0 7

RESET

 

 

 

fXC

CLK

 

 

TxRDY

 

 

 

 

WR

TxD

 

TRANSMIT

TxE

CS

TxEMPTY

 

 

CONTROL

 

C/O

CTS

 

 

 

RD

SYNDET

 

 

 

RxRDY

TxRDY

 

 

 

Pin Name

Pin Function

Pin Name

Pin Function

07- 0 0

Data Bus (8 bits)

DSR

Data Set Ready

C/O

Control or Data is to be Written or Read

DTR

Data Terminal Ready

AD

Read Data Command

SYNDET

Sync Detect

WR

Write Data or Control Command

RTS

Request to Send Data

Cs

Chip Enable

CTS

Clear to Send Data

CLK

Clock Pulse (TTL)

TxE

Transmitter Empty

RESET

Reset

Vee

+5 Volt Supply

TxC

Transmitter Clock

GND

Ground

TxD

Transmitter Data

 

 

RxC

Receiver Clock

 

 

RxD

Receiver Data

 

 

RxRDY

Receiver Ready (has character for 8080)

 

 

TxRDY

Transmitter Ready (ready for char. from 8080)

 

 

 

RxD

/

RxRDY

RxC

INTERNAL

 

DATA BUS

..... SYNDET

 

5-135

Page 202 Page 204
Page 203
Image 203
Intel 8080 manual Programmable Communication Interface
Page 202 Page 204

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.
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