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Serial Communication

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30 views36 pages

Serial Communication

Uploaded by

tekiyagaming
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
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Serial Communication

Thareendhra Keerthi Wijayasiriwardhane


Department of Industrial Management
Faculty of Science
University of Kelaniya
thareen@kln.ac.lk
Learning Outcomes
 On completion of this session, you should be able to
 Discuss serial vs. parallel communications in the context
of embedded systems
 Contrast asynchronous vs. synchronous communications
 Explain asynchronous data transfer protocol
 Explain need of Line Drivers/USART to USB interfaces
 Explain how Tx and Rx transmit and receive data
 Explain the functionality of USART registers
 Construct a microcontroller-based system and program it
to communicate with another system

2
Serial Communication
 Used by embedded systems to communicate with other
systems
 What are other systems?

 Sends 1 bit at a time


 Why not parallel?

3
USART
 A peripheral device that implements both
asynchronous and synchronous serial communications
 Asynchronous
 Synchronous
 Why separate
peripheral
device for data
communication?

4
Asynchronous Data Transfer
 Each character is framed between a start bit and a stop
bit and then transmitted
 Why baud rate is important?
 How can receiver recognize transmitted characters?

5
Connection over Serial Port
 Using a Line Driver
 Why not connect directly?

6
Arduino Severino
 ATmega328P with MAX232

7
Connection over USB Port
 Using a UART to USB interface controller

8
Arduino Duemilanove
 ATmega328P
with FT232RL

9
Connection over USB Port
 Using another Microcontroller as UART to USB
interface controller

10
Arduino Uno
 ATmega328P
with ATmega16U2

11
Asynchronous Transmitter

 Which flag (UDRE or TXC) gives maximum throughput?


 What’s the purpose of TXC flag?

12
Asynchronous Receiver

 What’s the role of Pin Control?


 What’s the need of Shift Registers?

13
USART Registers
 UBRRn (USART Baud Rate Register n)
 Used to set baud rate
 16-bit register but only 12 bits are used

14
USART Registers
 UDRn (USART Data Register n)
 Refers to Transmit Data Buffer that holds the character
to be transferred to Transmit Shift Register
 Also refers to Receive Data Buffer that holds the
character transferred from Receive Shift Register

15
USART Registers
 UCSRnA (USART Control and Status Register n A)

 RXCn (Receive Complete) flag bit is set when UDRn


contains unread data
 TXCn (Transmit Complete) flag bit is set when entire
frame in Transmit Shift Register has been shifted out and
UDRn is empty
 UDREn (USART Data Register Empty) flag bit is set
when UDRn becomes empty

16
USART Registers
 UCSRnB (USART Control and Status Register n B)

 RXCIEn (Receive Complete Interrupt Enable) bit and


TXCIEn (Transmit Complete Interrupt Enable) bit
enable interrupts on RXCn and TXCn flags, respectively
 UDRIEn (USART Data Register empty Interrupt
Enable) bit enables interrupt on UDREn flag
 RXENn (Receiver ENable) and TXENn (Transmitter
ENable) bits enable RX and TX, respectively
 What is the need of enabling and disabling RX and TX?

17
USART Registers
 UCSRnC (USART Control and Status Register n C)

 UCSZn0 (USART Character SiZe), UCSZn1 bits and


UCSZn2 bit of UCSRnB specify character size for
communication
UCSZn2 UCSZn1 UCSZn0 Character Size
0 0 0 5-bit
0 0 1 6-bit
0 1 0 7-bit
0 1 1 8-bit
1 1 1 9-bit

18
System 16
charEncloser - Receives characters
from PC, encloses them with
square brackets and transmits
enclosed characters back to PC

19
ATmega328P USART Pinout

20
Hardware
 Schematic Diagram

21
Hardware
 Wiring Diagram

22
Firmware
 Algorithm

23
Setting Baud Rate
 Select a standard baud rate from 2400, 4800, 9600,
14400, 19200, 28800, 38400, 57600, 76800, 115200,
230400, 460800, to 921600 bps
 Why not other values?
 Set the baud rate
 Determine and
set the value of UBRR

 Why do you need to add UL suffix?

24
Baud Rate Error
 Determine actual baud rate

 Calculate baud rate error

 What would happen if a baud rate


with higher error % is used?
 How to minimize baud rate error?

25
C Program

26
Extending IDE with a Terminal
 What’s a
Terminal
Emulator?

27
Communicating over Terminal
 What are CR
and LF?

28
Firmware
 Algorithm for Arduino

29
Firmware
 Source Code (using Arduino Wrapper Functions)

30
Serial Monitor
 Terminal emulator of Arduino IDE

31
System 17
charEncloserUsingInterrupts -
Receives characters from PC,
encloses them with square brackets
and transmits enclosed characters
back to PC using interrupts

32
Firmware
 Algorithm

33
C Program

34
Using Labeled Constants

35
Questions

36

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