electronics- serial communication-uart

Serial Communication -UARTUART or Serial Console

Raspberry Pi Python Serial Library

ElectronicsSerial Communication-UART

Terry Sturtevant

Wilfrid Laurier University

November 7, 2018

Terry Sturtevant Electronics Serial Communication-UART


Raspberry Pi Python Serial LibraryBaud rate calculationRS232 communication

Serial Communication -UART

Universal Asynchronous Receiver TransmitterSimplest form of serial communicationBetween 2 devicesUses 2 signals (and Ground), Rx and TxAsynchronous, so both must agree on baud rate





Universal Asynchronous Receiver Transmitter

Simplest form of serial communicationBetween 2 devicesUses 2 signals (and Ground), Rx and TxAsynchronous, so both must agree on baud rate





Universal Asynchronous Receiver TransmitterSimplest form of serial communication

Between 2 devicesUses 2 signals (and Ground), Rx and TxAsynchronous, so both must agree on baud rate





Universal Asynchronous Receiver TransmitterSimplest form of serial communicationBetween 2 devices

Uses 2 signals (and Ground), Rx and TxAsynchronous, so both must agree on baud rate





Universal Asynchronous Receiver TransmitterSimplest form of serial communicationBetween 2 devicesUses 2 signals (and Ground), Rx and Tx

Asynchronous, so both must agree on baud rate





Universal Asynchronous Receiver TransmitterSimplest form of serial communicationBetween 2 devicesUses 2 signals (and Ground), Rx and TxAsynchronous, so both must agree on baud rate




Communication parameters

1 Start bit at “0” levelLSB transmitted firstCan have odd, even, or no parity bit1 or 2 Stop bits at “1” level

Since start and stop bits are opposite, new characters can alwaysbe detected.





1 Start bit at “0” level

LSB transmitted firstCan have odd, even, or no parity bit1 or 2 Stop bits at “1” level






1 Start bit at “0” levelLSB transmitted first

Can have odd, even, or no parity bit1 or 2 Stop bits at “1” level






1 Start bit at “0” levelLSB transmitted firstCan have odd, even, or no parity bit

1 or 2 Stop bits at “1” level






1 Start bit at “0” levelLSB transmitted firstCan have odd, even, or no parity bit1 or 2 Stop bits at “1” level





Start




Start

0

LSB

1




Start

0

LSB

1

1 1




Start

0

LSB

1 2

1 1 1




Start

0

LSB

1 2 3

1 1 1 0




Start

0

LSB

1 2 3 4

1 1 1 0 0




Start

0

LSB

1 2 3 4 5

1 1 1 0 0 1




Start

0

LSB

1 2 3 4 5 6

1 1 1 0 0 1 1




Start

0

LSB

1 2 3 4 5 6 7

MSB

1 1 1 0 0 1 1 0




Start Stop

0

LSB

1 2 3 4 5 6 7

MSB

1 1 1 0 0 1 1 0




Start Stop

0

LSB

1 2 3 4 5 6 7

MSB

1 1 1 0 0 1 1 0

UART no parity - 01100111




Start Stop

Parity0 1 2 3 4 5 6 7

UART even parity




Start Stop

Parity0 1 2 3 4 5 6 7

UART odd parity




Baud rate calculation

Baud rate is the number of bits possible in a seconde.g. 9600 baud → 1 bit takes 1

9600 secondAfter start bit is detected, wait time for 11

2 bit to testfor first data bit and then after every 1 bit intervalResetting at the start bit allows some clock variation





Baud rate is the number of bits possible in a second

e.g. 9600 baud → 1 bit takes 19600 second

After start bit is detected, wait time for 112 bit to test

for first data bit and then after every 1 bit intervalResetting at the start bit allows some clock variation






9600 second

After start bit is detected, wait time for 112 bit to test

for first data bit and then after every 1 bit intervalResetting at the start bit allows some clock variation







2 bit to testfor first data bit and then after every 1 bit interval

Resetting at the start bit allows some clock variation







2 bit to testfor first data bit and then after every 1 bit intervalResetting at the start bit allows some clock variation




Start




Start

0

1




Start

0 1

1 1




Start

0 1 2

1 1 1




Start

0 1 2 3

1 1 1 0




Start

0 1 2 3 4

1 1 1 0 0




Start

0 1 2 3 4 5

1 1 1 0 0 1




Start

0 1 2 3 4 5 6

1 1 1 0 0 1 1




Start

0 1 2 3 4 5 6 7

1 1 1 0 0 1 1 0




Start Stop

0 1 2 3 4 5 6 7

1 1 1 0 0 1 1 0




Start Stop

0 1 2 3 4 5 6 7

1 1 1 0 0 1 1 0

Bit timing




RS232 communication

Voltages are inverted±3→ ±12Zero is not a valid voltageMark level (inactive/1) is a negative voltageSpace level (active/0) is a positive voltage




RS232 communication

Voltages are inverted

±3→ ±12Zero is not a valid voltageMark level (inactive/1) is a negative voltageSpace level (active/0) is a positive voltage




RS232 communication

Voltages are inverted±3→ ±12

Zero is not a valid voltageMark level (inactive/1) is a negative voltageSpace level (active/0) is a positive voltage




RS232 communication

Voltages are inverted±3→ ±12Zero is not a valid voltage

Mark level (inactive/1) is a negative voltageSpace level (active/0) is a positive voltage




RS232 communication

Voltages are inverted±3→ ±12Zero is not a valid voltageMark level (inactive/1) is a negative voltage

Space level (active/0) is a positive voltage




RS232 communication

Voltages are inverted±3→ ±12Zero is not a valid voltageMark level (inactive/1) is a negative voltageSpace level (active/0) is a positive voltage




ParityMark 0 1 2 3 4 5 6 7




Start

ParityMark

Space

0 1 2 3 4 5 6 7




Start Stop

ParityMark

Space

0 1 2 3 4 5 6 7




Start Stop

ParityMark

Space

0 1 2 3 4 5 6 7

RS232 levels




UART or Serial Console

On the Raspberry Pi, the serial console uses the UART→ the UART isn’t available for other devicesThe serial console can be disabledThis means you need to connect to monitor, keyboard, etc.





On the Raspberry Pi, the serial console uses the UART

→ the UART isn’t available for other devicesThe serial console can be disabledThis means you need to connect to monitor, keyboard, etc.





On the Raspberry Pi, the serial console uses the UART→ the UART isn’t available for other devices

The serial console can be disabledThis means you need to connect to monitor, keyboard, etc.





On the Raspberry Pi, the serial console uses the UART→ the UART isn’t available for other devicesThe serial console can be disabled

This means you need to connect to monitor, keyboard, etc.





On the Raspberry Pi, the serial console uses the UART→ the UART isn’t available for other devicesThe serial console can be disabledThis means you need to connect to monitor, keyboard, etc.




There is a script to enable and disable the serial console

sudo rpi-serial-console disablewill disable the consolesudo rpi-serial-console enablewill enable the console

Remember you probably don’t want to be using thiscommand from within the serial console.




There is a script to enable and disable the serial consolesudo rpi-serial-console disablewill disable the console

sudo rpi-serial-console enablewill enable the console





There is a script to enable and disable the serial consolesudo rpi-serial-console disablewill disable the consolesudo rpi-serial-console enablewill enable the console





PySerial

ser = serial.Serial()open portser.baudrate = 19200set baudrateser.port =’//dev//ttyAMA0’set portser.is openreturns True if open, False if not




PySerial

ser = serial.Serial()open port

ser.baudrate = 19200set baudrateser.port =’//dev//ttyAMA0’set portser.is openreturns True if open, False if not




PySerial

ser = serial.Serial()open portser.baudrate = 19200set baudrate

ser.port =’//dev//ttyAMA0’set portser.is openreturns True if open, False if not




PySerial

ser = serial.Serial()open portser.baudrate = 19200set baudrateser.port =’//dev//ttyAMA0’set port

ser.is openreturns True if open, False if not




PySerial

ser = serial.Serial()open portser.baudrate = 19200set baudrateser.port =’//dev//ttyAMA0’set portser.is openreturns True if open, False if not




PySerial (continued)

ser.write(b’string’)write stringser.read(10)read 10 bytes (or until timeout)ser.readline()read until ’\n’ receivedser.close()close port





ser.write(b’string’)write string

ser.read(10)read 10 bytes (or until timeout)ser.readline()read until ’\n’ receivedser.close()close port





ser.write(b’string’)write stringser.read(10)read 10 bytes (or until timeout)

ser.readline()read until ’\n’ receivedser.close()close port





ser.write(b’string’)write stringser.read(10)read 10 bytes (or until timeout)ser.readline()read until ’\n’ received

ser.close()close port





ser.write(b’string’)write stringser.read(10)read 10 bytes (or until timeout)ser.readline()read until ’\n’ receivedser.close()close port




PySerial sample code

i m p o r t s e r i a ls e r = s e r i a l . S e r i a l (”/ dev /ttyAMA0 ”)s e r . b a u d r a t e = 9600data = s e r . r e a d ( 1 0 )#data = s e r . r e a d l i n e ( )s e r . w r i t e ( data )s e r . c l o s e ( )


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