7 Serial Uart

8/6/2019 7 Serial Uart

1/21

Serial Communication

Introduction

Parallel Communication is a communication bit of the data are

transferred between source and destination parallelly. Example of the parallel

communication is a port of the MCS-51 which is transfer data every bit in the

same time.

Serial Communication is a communication that separate data into bit

and send the data from source and destination bit-by-bit. There are 2 major types of

the serial communication. First type is a Synchronous Serial Communication which

has reference clock between source and destination in order to make the data that

transfer in communication correct. Asynchronous Serial Communication is the secondtype. In this communication, there is no clock to synchronous bit but rather use

Band Rate in order to correct to data.
http://www.pdfonline.com/easypdf/?gad=CLjUiqcCEgjbNejkqKEugRjG27j-AyCw_-AP


2/21

Introduction

Introduction

Synchronous Serial Communication

Asynchronous Serial Communication


3/21

Introduction

TxD pin 11 of the 8051 (P3.1)

Data Transmitting Pin

RxD pin 10 of the 8051 (P3.0)

Data Receive Pin

Mode of Serial Communication

Walky-Talky


4/21

UART

A universal asynchronous receiver/transmitter (usually abbreviated UART)

is a type of "asynchronous receiver/transmitter", a piece of computer hardware thattranslates data between parallel and serial forms. UARTs are commonly used in

conjunction with other communication standards such as EIA RS-232.

A UART is usually an individual (or part of an) integrated circuit used for

serial communications over a computer or peripheral device serial port. UARTs are

now commonly included in microcontrollers. A dual UART or DUART combines

two UARTs into a single chip. Many modern ICs now come with a UART that can

also communicate synchronously; these devices are called USARTs.

UART

Start bit Data Stop bit


5/21

Baud Rate

In telecommunications and electronics, baud, is the unit of

symbol rate, the number of distinct symbol changes

(signalling events) made to the transmission medium per

second in a digitally modulated signal.

The symbol rate (expressed in baud) is distinct from the

bit rate (expressed in bit/s). One symbol can carry more

than one bit of information. In voiceband modems, where

spectral efficiency is important, it is common for one

symbol to carry 3 or more bits.

RS-232 Standard

The RS-232 standard defines the voltage levels that

correspond to logical one and logical zero levels. Valid signals are plus

or minus 3 to 15 volts. The range near zero volts is not a valid RS-232

level;

logic one is defined as a negative voltage, the signal condition

is called marking, and has the functional significance of OFF.

Logic zero is positive, the signal condition is spacing, and has

the function ON.

The standard specifies a maximum open-circuit voltage of 25 volts;signal levels of 5 V,10 V,12 V, and 15 V are all commonly seen

depending on the power supplies available within a device. RS-232

drivers and receivers must be able to withstand indefinite short circuit

to ground or to any voltage level up to +/-25 volts. The slew rate, or

how fast the signal changes between levels, is also controlled.


6/21

RS-232 Standard

RS-232 Standard (DB-9)


7/21

Serial Communication For Multi-CPU

RS-232 Driver


8/21

RS-232 Driver

RS-232 Driver


9/21

RS-232 Driver

Serial Communication Register

SBUF (Serial Buffer)


10/21


SBUF (Serial Buffer)


Bit interrupt from Receive DataRI (Receive interrupt flag)

Bit interrupt from Transmit DataTI (Transmit interrupt flag)

Enable Receive

1 enable

0 disable

REN (Received enable bit)

9th Bit for Receive Data in Mode 2,3RB8 (Receive bit #8)

9th Bit for Transmit Data in Mode 2,3TB8 (Transmit bit #8)


11/21


Variable (Set by Timer)UART 9 bit311

Fixed (Frequency of X-tal /32 or /64)UART 9 bit201

Variable (Set by Timer)UART 8 bit110

Fixed (Frequency of X-tal /12)Shift Register000

Baud RateDetailModeSM1SM0

Serial Communication Mode 0

In this mode, MCS-51 will receive data and send data by pin RxD and pin TxD is

used to send Shift Clock. Eight bits are transmitted and received with the least-significant (LSB)

first. The baud rate is fixed at 1/12th the on-chip oscillation frequency. The RxD is used for

both data input and output and the TxD line serves as the clock. Data in this mode is only

8 bits and baud rate is the crystal frequency divided by 12


12/21




13/21

Serial Communication Mode 1,2,3

In mode 2, MCS-51 will transmit and receive 11 bit data which is consisted of

1 start bit 8 data bit 1 parity bit (used to check error) and 1 stop bit. Data will receive and

transmit through SBUF Register and baud rate of the serial communication is set by SMOD.

If SMOD in PCON register is clear then the baud rate is equal to crystal frequency / 64 and if

it is set then baud rate equals to crystal frequency / 32.

In mode 1, MCS-51 will transmit and receive 10 bit data which is consisted of1 start bit 8 data bit and 1 stop bit. Data will receive and transmit through SBUF Register

and baud rate of the serial communication in this mode can be set by using Timer1

In mode 3, MCS-51 will transmit and receive 11 bit data which is consisted of1 start bit 8 data bit 1 parity bit (used to check error) and 1 stop bit Data will receive and

transmit through SBUF Register and baud rate of the serial communication in this mode

can be set by using Timer1

Baud Rate Generator Mode 1,3

)1(32

2RateOverflowTimerRateBaud

SMOD

Normally, Timer1 is used in mode 2 in order to set the baud rate

))]1(256[12

(32

2

TH

FrequencyOscillatorRateBaud

SMOD

SMOD is a bit in PCON register and called Double Baud Rate


14/21


IDLPDGF0GF1------SMOD

D7 D0

MOV A,PCON ;place a copy of PCON in ACC

SETB ACC.7 ;make D7=1

MOV PCON,A ;now SMOD=1 without

;changing any other bits

PCON



15/21


Example

if we need baud rate equal to 9600 when crystal

of the 8051 system = 11.0592 MHz and check for Double Baud Rate

and no Double Baud Rate

))]1(256[12

100592.11(

32

29600

61

TH

x

TH1 = 256 6 = 250

= FAH

))]1(256[12

100592.11(

32

29600

60

TH

x

TH1 = 256 3 = 253

= FDH



16/21


Examples

ORG 0000H ; Code Start at Address 0000H

JMP START ; Go to Start Label

ORG 0100H ; Code Start at Address 0100H

START: CALL INIT_SE

MOV A,#'1'

CALL COUT

MOV A,#'Y'

CALL COUT

JMP $

INIT_SE: MOV SCON,#50H

MOV TMOD,#20H

MOV TH1,#0FDHSETB TR1

SETB TI

RET

COUT: JNB TI,COUT

CLR TI

MOV SBUF,A

RET

END


17/21

Examples

Examples


18/21

Examples

Examples


19/21

Examples

Examples


20/21

Examples

Examples


21/21

Examples

Question ??????

7 Serial Uart

Documents

Transcript of 7 Serial Uart