Lecture 4 i2 c bus & interrupts

Workshop

Project Pedagogy approach ofMicrocontroller

Project Pedagogy approach of Microcontroller – Palestinian Robotic Cup 1

Microcontroller

PTC Khadoury IUT Cachan

Palestinian Robotic Cup

4. I²C bus & interrupts

connecting and using an ultrasonic i²c sensor


PTC Khadoury IUT Cachan

Why do you need ultrasonic telemeter ?


Blanche neige accident.MOV

without telemeter with telemeter

valetpique.mov

jack &

Commands

Energy

I2C

PWMOutputs

Digital

communicationperipherals Chopper

+ Motors

ultrasonic

telemeter

UART


LCD

Display

jack &

buttons

line info

Micro-

controller

DigitalInput

Analog to digital

converter

Digitaloutputs

Fast counting

Inputs

Analog to digital

converter

Infrared

sensors

Motors

encoders

positioninfo

Potentio-

meter

4.1 The ultrasonic telemeter SRF08

4.2 I²C physical & protocol layers

4 I²C bus & interrupts


4.3 Using the telemeter by pooling

4.4 interrupts

4.5 Using the telemeter with interrupts


piezoelectricemitter

physics principle


piezoelectricreceiver

d = c.t

distance (m)

sound speedthrough the air (~340 m.s-1)

flight time (s)

4.1 The ultrasonic telemeter SRF08internals registers


initialization : 1 meter and result in centimeter

Measurement request

Waiting for 10 ms

Read result (between 0 and 100)


1234

I2C

Header 4

SCLSDAVDD

connections


Header 4

SRF08 sensor pins

Microcontroller boardI²C connector

for more details, see www.robot-electronics.co.uk

4.2 I²C physical & protocol layers


4.2 I²C physical and protocol layers

I²C overview

Inter Integrated Circuits bus

2-wires synchronous bus


Up to 15 Mbits/s

Multi-master mode is possible

Up to 127 devices on the bus


physical layer : 2-wires synchronous bus

Sensor(slave mode)

Memory(slave mode)

Microcontroller(Master Mode)

Real TimeClock

(slave mode)addr = 0xE0addr = 0xAC addr = 0xB4


GND

VCC = 5Vpull-up resistors

SCL (clock wire)

SDA (data wire)


frames

Transmit addressof Slave (W) Ack

Transmit registernumber to write

Transmit data StopStart

frame to write

Sensor(slave mode)address 0xE0


Ack Ack

Write address 0xE0Read address 0xE1


GND

pull-up resistors

SCL (clock wire)

SDA (data wire)

address 0xE0


framesTransmit address

of Slave (W)

Transmit registernumber to read

Receive registerdata from Slave

Start

frame to read

Transmit addressof Slave (R)

ReStart Stop

Sensor(slave mode)address 0xE0


Ack Ack

Ack NAck

Project Pedagogy approach of Microcontroller – Palestinian Robotic Cup 15GND

pull-up resistors

SCL (clock wire)

SDA (data wire)

address 0xE0(Master Mode)


For more details,see I2C_BUS_SPECIFICATION_3.pdf


see I2C_BUS_SPECIFICATION_3.pdf

4.3 Using the telemeter by polling


4.3 Using the telemeter by polling

I²C configuration

See - Microchip PIC18F4550 datasheet (ch. 19)- Microchip C18 library

SSPADD = 118;OpenI2C(MASTER,SLEW_ON);


configure I²C peripheral(Master and 400 kHz mode)

initialization : 1 meter and result in centimeter

Measurement request

Waiting for 10 ms

Read result

4.3 Using telemeter by polling


Read result

void SRF_initialisation(char address);unsigned char SRF_read_byte( unsigned char address, unsigned char reg );unsigned char SRF_write_byte( unsigned char address, unsigned char reg,

unsigned char data );

library SRF08

Timer3

4.4 Interrupts


4.4 Interrupts

4.5 Interrupts

What is an interrupt ?

Measurement request

Waiting for 10 ms

Read result

initialization

main program


measurement

request

CP

U

occupation

CPU is reading

the value of the timer3

read

result

CPU is reading

the value of the timer3

measurement

request

read

result

…

4.5 Interrupts

What is an interrupt ?

initialization

Measurement request

Read result

main program interrupt subroutine


measurement

request

CP

U

occupation

read

result

measurement

request

read

result

…the CPU is free the CPU is free

4.5 Interrupts

interrupt in Microchip PIC18Fxxxx

different interrupt sources :- Timers- External pins- USART / USB / I2C- …

for each interrupt source, 2 bits :- One Flag bit


- One Flag bit- One Enable bit

and sometimes- One Priority bit

and, for all interrupts :Two bits : - GIE (Global interrupt enable)- PEIE (Peripherals Interrupt enable)

Peripheral Interrupt Enable registers (PIE1 and PIE2).

PIE1 = 0b00000000;

SPPIE ADIE TXIE TMR2IE TMR1IESSPIERCIE CCP1IE

4.5 Interrupts



PIE2 = 0b00000010;

OSCFIE CMIE EEIE TMR3IE CCP2IEBCLIE

SPPIE ADIE TXIE TMR2IE TMR1IESSPIERCIE CCP1IE

USBIE HLVDIE

Peripheral Interrupt Request (Flag) registers (PIR1 and PIR2).

PIR1 = 0b00000000;

SPPIF ADIF TXIF TMR2IF TMR1IFSSPIFRCIF CCP1IF


4.5 Interrupts


PIR2 = 0b00000000;

OSCFIF CMIF EEIF TMR3IF CCP2IFBCLIF

SPPIF ADIF TXIF TMR2IF TMR1IFSSPIFRCIF CCP1IF

USBIF HLVDIF

What happens when an interrupt occurs ?


4.5 Interrupts

The program executes the instruction which is at the address 0x08 in the program memory

Programcounter goto Interrupt funct


main program

Interrupt function

ProgramcounterProgramcounter

ProgramcounterProgramcounter

Programcounter

Flow chart

initialization

Measurement request

Read result

main program interrupt subroutine



measurement

request

CP

U

occupation

read

result

measurement

request

read

result

…the CPU is free the CPU is free


1st : initialize the I²C bus and the sensor

3rd : unmask the interrupts you need (TMR3IE)

2nd : configure Timer3 (OpenTimer3(…))

4th : unmask interrupts (GIE and PEIE)

5th : write the infinite loop

main program

Interrupt subroutine


6th : write the interruption subroutine (Reading value & measurement request)

Interrupt subroutine

7th : write the declaration of this ISR on top of main file

8th : write the branch to go to this ISR


Interrupt subroutine6th : write the interruption subroutine (Reading value & measurement request)

#pragma interrupt TMR3_Interrupt_function

void TMR3_Interrupt_function(void)

{

if (PIR2bits.TMR3IF == 1)

{... }//end if

)// end TMR3_Interrupt_function

it indicates that the following function is an ISR

it verifies if this is the timer3 which set on the interrupt


)// end TMR3_Interrupt_function

8th : write the branch to go to this ISR

#pragma code high_vector=0x08

void high_vector (void)

{ _asm goto TMR3_Interrupt_function _endasm }

#pragma code

it indicates that the nextcode is at the adress 0x08

it indicates that the nextcode is in the program memory

_asm and _endasm frame an asm instruction

on the interrupt

Lecture 4 i2 c bus & interrupts

Technology

Transcript of Lecture 4 i2 c bus & interrupts