Aum Amriteswaryai Namah:

PIN DIAGRAMWhen two processors are to communicate, more often the communication is organized in a bit serial fashion

The communication may be

simplex transmissionhalf duplex

full duplex

Asynchronous Communication

GNDGND

Tx Rx

Processor A Processor B

Connection for simplex serial transmission between two Cs

•The two processors should communicate bit streams at a prearranged bit rate called ‘baud rate’ •Baud rate represents the number of bits per second at which the transmission and reception between the two processors take place

Consider the implementation of a scheme at 9.6 K baud. •It implies transmission at 9600 bits per sec •each bit takes 104.25μs for transmission

•both the Cs will have a clock of 104.25μs time period; it is called the ‘baud rate generator’;

P

Q

Startbit

b0 b1 b2 b3 b4 b5 b6 b7Stopbit

0 11 00000 11

0 11 00000 11

s25.104

Transmitter baud rategenerator output

Transmitted bitsequence

Transmittedwaveform

Transmitted 10 bitserial sequence

Receiver baud rategenerator

Set of ten receivedbits

Asynchronous transmission of a byte at 9.6 kbaud

GNDGND

Tx

Rx

Processor A Processor B

Tx

Rx

Vcc Vcc

Connection for half duplex serial transmission between two Cs

GNDGND

Tx

Rx

Processor A Processor B

Tx

Rx

Connection for full duplex serial transmission between two Cs

Synchronous Communication

GNDGND

Tx / Rx Tx / Rx

Processor A Processor B

Clk Clk

Connection for synchronous half duplex transmission between two Cs

GNDGNDTx Rx

Processor A Processor BClk Clk

TxRx

Connection for synchronous full duplex transmission between two Cs

GND

Tx

Processor A

Rx

Vcc

GND

Tx

Processor B

Rx

Vcc

GND

Tx

Processor C

Rx

Vcc

GND

Tx

Processor D

Rx

Vcc

Four Cs connected for communication amongst them in half duplex asynchronous mode

Processor Address

A 01h

B 02h

C 03h

D 04h

Address assignments to different Cs in Figure

USART and Overheads

‘Universal Synchronous Asynchronous Receiver Transmitter (USART)’ – a module which carries out the serial communication

The simplest USART will have the following features.

A baud rate generator. Parallel to Serial Converter:Insertion of additional bits: Data recovery at Receiver: Programmability:Bit checks: Buffers: Interrupts: Error Indication:

The PIC16 series have an USART built in with a transmitter block and a receiver block within

Baud Rate Generator

)1(4

X

Fbaudrate osc

The number X is to be loaded into SPBRG register

The baud rate is derived from the processor clock by dividing it by a selected byte – X – in the 0 to 255 range.

In synchronous mode In asynchronous mode

)1(16

X

Fbaudrate osc

)1(64

X

Fbaudrate osc

or

Data bus8

8

TXREG register

TSR register

Pin buffer &control

Tx / CK pin

b0b8

TMRTSPEN

Baud rate clock

Baud rate generattor

SPBRG

TXENTX9D

TX9

TXIF

TXIE

interrupt

SPEN

Data bus8

8

RSR register

Pin buffer &control

Rx / DT pin

b8b0

SPEN

Baud rate clock

Baud rate generattor

SPBRG

RX9

RCIF

RCIE

interrupt

stopstart

RX9DRCREG register

Datarecovery

FERROERRCREN

FIFO

Nine-Bit Transmission

Tx9 [TXSTA<b6>] and RX9 [RCSTA<b6>] are to be set to select the 9 bit scheme .

Can be used for two purposes

1. As address/data indication bitWhen the master sends out bytes, the first one can be the address. Bit – b8 – can be set indicating that the associated byte is an address. All slaves sense b8; if b8 = 1, they check for an address match; each can accept further bytes only if it finds an address match.

2. As Parity bit

Now..,try this out!!!!!!

? Calculate the baud rate error for the following conditions:

FOSC = 16 MHz

Desired Baud Rate = 9600

BRGH = 0

SYNC = 0

Solution