82512 - Topics 2102440 Introduction to Microprocessors...

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Unformatted text preview: Topics 2102440 Introduction to Microprocessors Chapter 12 Serial Communications Suree Pumrin, Ph.D. 1 2102440 Introduction to Microprocessors Sync vs Asynchronous RS-232C 8251 USART 8251 Initialization 2 Serial vs. Parallel Data Transfer Serial Transfer Sender Receiver Synchronous vs. Asynchronous A communication protocol is a convention for data transmission that that include such functions as timing, control, formatting, and data presentation. There are two categories depending on the clocking of the data on the serial link: Synchronous protocols--each successive datum in a stream of data is protocols--each governed by a master clock and appears at a specific interval in time. Asynchronous protocols--successive data appear in the data stream at protocols--successive arbitrary times, with no specific clock control governing the relative relative delays between data. Serial communication uses a single line data. Parallel Transfer D0 Parallel communication uses n-bit data line. Sender Receiver There are special IC chips made for serial data communications. These chip is called UART (universal asynchronous receiverreceivertransmitter) and USART (universal synchronous-asynchronous synchronousreceiver-transmitter). receiver- D7 2102440 Introduction to Microprocessors 3 2102440 Introduction to Microprocessors 4 Synchronous Data Communication Transmit data Receive data Clock Signal common Asynchronous Data Communication Transmit data Receive data Signal common System 1 System 2 System 1 System 2 MSB LSB Data SYN CHAR #2 SYN CHAR #1 Synchronous data-transmission format 2102440 Introduction to Microprocessors Parity bit Stop bit (MARK) Data Start bit (SPACE) Asynchronous data-transmission format 5 2102440 Introduction to Microprocessors 6 RS-232C A widely accepted interface standard originally developed to foster data communication on public telephone network through a modem (modulatordemodulator). This has been adapted to the communication of terminals (PCs) directly to computers. RS-232C interface with communications equipment 2102440 Introduction to Microprocessors 7 2102440 Introduction to Microprocessors 8 RS-232C Interface, Terminal/computer to Terminal/computer 8251 USART The 8251 USART (Universal Synchronous Asynchronous Receiver Transmitter) is capable of implementing either an asynchronous or synchronous serial data communication. As a peripheral device of a microcomputer system, the 8251 receives parallel data from the CPU and transmits serial data after conversion. This device also receives serial data from the outside and transmits parallel data to the CPU after conversion. 2102440 Introduction to Microprocessors 9 2102440 Introduction to Microprocessors 10 Block diagram of 8251 Read/write operation of 8251 2102440 Introduction to Microprocessors 11 2102440 Introduction to Microprocessors 12 8251 Initialization P o w e r-o n R e s e t Load m ode in s t r u c t io n Async? Y N Load syn char Load com m and in s t r u c t io n Before the 8251 can be used to receiver or transmit characters, its mode control and command registers must be initialized. The 8251 has only one address for a few control registers. The only readable register is a status register. The other registers must be written in sequence. Y R e s e t? N 2102440 Introduction to Microprocessors 13 ...
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This note was uploaded on 02/23/2012 for the course CS 101 taught by Professor Martand during the Spring '10 term at Punjab Engineering College.

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