Serial data transfer

Serial Data Transfer

8051

Serial vs Parallel Data Transfer

SERIAL COMMUNICATION(TELEPHONE LINE):

• long distance • cheaper• one bit/data line

PARALLEL COMMUNICATION (PRINTER):• fast• distance cannot be greater• expensive

SERIAL COMMUNICATION

PISO SHIFT REGISTER

SIPO SHIFT REGISTER

DA CONVERTER

AD CONVERTER

Start bit—indicates the beginning of the data word

Stop bit—indicates the end of the data word

Parity bit—added for error detection (optional)

Data bits—the actual data to be transmitted

Baud rate—the bit rate of the serial port

Basic Terms:

Asynchronous Serial Communication

• With asynchronous communication, the transmitter and receiver do not share a common clock

Transmitter Receiver+

1 byte-wide Data

Data–

1 byte-wide Data

The Receiver

Extracts the data using its own clock

Converts the serial data back to the parallel form after stripping off the start, stop and parity bits

The Transmitter

Shifts the parallel data onto the serial line using its own clock

Also adds the start, stop and parity check bits

Add: Start, Stop, Parity Bits

Remove: Start, Stop, Parity Bits

• Asynchronous transmission is easy to implement but less efficient as it requires an extra 2-3 control bits for every 8 data bits

• This method is usually used for low volume transmission

D0 D1 D2 D3 D4 D5 D6 D7

Start Bit 1 or 2 Stop Bits Parity Bit

1 Asynchronous Byte

Synchronous Serial Communication

• In the synchronous mode, the transmitter and receiver share a common clock

• The transmitter typically provides the clock as a separate signal in addition to the serial data

Transmitter Receiver

Data

Clock

The Receiver

Extracts the data using

the clock provided by the

transmitter

Converts the serial data

back to the parallel form

The Transmitter

Shifts the data onto the serial

line using its own clock

Provides the clock as a

separate signal

No start, stop, or parity bits

added to data

1 byte-wide Data

1 byte-wide Data

9 Pin Connector on a DTE device (PC connection)

Male RS232 DB9

Pin Number Direction of signal:

1 Carrier Detect (CD) (from DCE) Incoming signal from a modem

2 Received Data (RD) Incoming Data from a DCE

3 Transmitted Data (TD) Outgoing Data to a DCE

4 Data Terminal Ready (DTR) Outgoing handshaking signal

5 Signal Ground Common reference voltage

6 Data Set Ready (DSR) Incoming handshaking signal

7 Request To Send (RTS) Outgoing flow control signal

8 Clear To Send (CTS) Incoming flow control signal

9 Ring Indicator (RI) (from DCE) Incoming signal from a modem

TXD(P3.1)

RXD(P3.0)

RXD

TXD

COM port of PC or device8051

How to Access UART?

• Each UART is accessed by two SFRs—SBUF and SCON

• The Serial Port Buffer (SBUF) is essentially two buffers: writing loads data to be transmitted to the buffer and reading accesses received data from the buffer.

• These are two separate and distinct buffers (registers): the transmit write-only buffer and the receive read-only register

• The Serial Port Control register (SCON) contains status and control bits

• The control bits set the operating mode for the serial port, and status bits indicate the end of the character transmission or reception

SCON Register:

OPERATING MODES OF SERIAL PORTS

• SERIAL PORT INTERFACE OF 8051 CAN BE OPERATED UNDER FOUR MODES:

MODE 0

MODE 1

MODE 2

MODE 3

MODE 0:(SIMPLE SHIFT REGISTER MODE)

• Serial data transmission and reception both are done through RXD pin

• 8 bits are transmitted or received with LSB first

• Asynchronous mode

• Only if R1=0, REN=1 reception is initiated

MODE 1:STANDARD UART

• Standard asynchronous serial communication mode

• 10 bits transmitted through TXD or received through RXD

• Start bit is active low signal and a stop bit is active high

• Baud rate is variable

2^SMOD\*oscillator frequency\(12*(256-(TH1))

• SMOD bit 0 or 1 in PCON

MODE 2:MULTIPROCESSOR MODE

• Supports asynchronous serial data transfer method

• 11 bits are transmitted or received

• 9th data bit can be assigned the value of 0 or 1 and 8 bit data is loaded into SBUF by programmer

o Baud rate =2^(SMOD)\64*(oscillator frequency)

MODE 3

• It is same as mode 2 in all aspects except the baud rate

• Baud rate is variable here

• Calculation of BR is similar to the mode 1 using timer 1

• 11 bits are transmitted or received here

• 11 bits consists of a start bit (0), 8 data bits (LSB first), a programmable 9th bit and a stop bit (1)