I²C bus & interrupts connecting and using an ultrasonic i²c sensor The ultrasonic telemeter SRF08 Using the telemeter with interrupts

1. Workshop
Project Pedagogy approach of
Microcontroller
Project Pedagogy approach of Microcontroller – Palestinian Robotic Cup 1
Microcontroller
PTC Khadoury IUT Cachan
Palestinian Robotic Cup

2. 4. I²C bus & interrupts
connecting and using an ultrasonic i²c sensor
Project Pedagogy approach of Microcontroller – Palestinian Robotic Cup 2
PTC Khadoury IUT Cachan

3. Why do you need ultrasonic telemeter ?
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Blanche neige accident.MOV
without telemeter with telemeter
valetpique.mov

4. jack &
Commands
Energy
I2C
PWM
Outputs
Digital
communication
peripherals Chopper
+ Motors
ultrasonic
telemeter
UART
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LCD
Display
jack &
buttons
line info
Micro-
controller
Digital
Input
Analog to
digital
converter
Digital
outputs
Fast
counting
Inputs
Analog to
digital
converter
Infrared
sensors
Motors
encoders
position
info
Potentio-
meter

5. jack &
Commands
Energy
I2C
PWM
Outputs
Digital
communication
peripherals Chopper
+ Motors
ultrasonic
telemeter
UART
Project Pedagogy approach of Microcontroller – Palestinian Robotic Cup 5
LCD
Display
jack &
buttons
line info
Micro-
controller
Digital
Input
Analog to
digital
converter
Digital
outputs
Fast
counting
Inputs
Analog to
digital
converter
Infrared
sensors
Motors
encoders
position
info
Potentio-
meter

6. 4.1 The ultrasonic telemeter SRF08
4.2 I²C physical & protocol layers
4 I²C bus & interrupts
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4.3 Using the telemeter by pooling
4.4 interrupts
4.5 Using the telemeter with interrupts

7. 4.1 The ultrasonic telemeter SRF08
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8. 4.1 The ultrasonic telemeter SRF08
piezoelectric
emitter
physics principle
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piezoelectric
receiver
d = c.t
distance (m)
sound speed
through the air (~340 m.s-1)
flight time (s)

9. 4.1 The ultrasonic telemeter SRF08
internals registers
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initialization : 1 meter and result in centimeter
Measurement request
Waiting for 10 ms
Read result (between 0 and 100)

10. 4.1 The ultrasonic telemeter SRF08
1
2
3
4
I2C
Header 4
SCL
SDA
VDD
connections
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Header 4
SRF08 sensor pins
Microcontroller board
I²C connector
for more details, see www.robot-electronics.co.uk

11. 4.2 I²C physical & protocol layers
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12. 4.2 I²C physical and protocol layers
I²C overview
Inter Integrated Circuits bus
2-wires synchronous bus
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Up to 15 Mbits/s
Multi-master mode is possible
Up to 127 devices on the bus

13. 4.2 I²C physical and protocol layers
physical layer : 2-wires synchronous bus
Sensor
(slave mode)
Memory
(slave mode)
Microcontroller
(Master Mode)
Real Time
Clock
(slave mode)
addr = 0xE0addr = 0xAC addr = 0xB4
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GND
VCC = 5V
pull-up resistors
SCL (clock wire)
SDA (data wire)

14. 4.2 I²C physical and protocol layers
frames
Transmit address
of Slave (W) Ack
Transmit register
number to write
Transmit data StopStart
frame to write
Sensor
(slave mode)
address 0xE0
Microcontroller
(Master Mode)
Ack Ack
Write address 0xE0
Read address 0xE1
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GND
pull-up resistors
SCL (clock wire)
SDA (data wire)
address 0xE0

15. 4.2 I²C physical and protocol layers
frames
Transmit address
of Slave (W)
Transmit register
number to read
Receive register
data from Slave
Start
frame to read
Transmit address
of Slave (R)
ReStart Stop
Sensor
(slave mode)
address 0xE0
Microcontroller
(Master Mode)
Ack Ack
Ack NAck
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GND
pull-up resistors
SCL (clock wire)
SDA (data wire)
address 0xE0
(Master Mode)

16. 4.2 I²C physical and protocol layers
For more details,
see I2C_BUS_SPECIFICATION_3.pdf
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see I2C_BUS_SPECIFICATION_3.pdf

17. 4.3 Using the telemeter by polling
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18. 4.3 Using the telemeter by polling
I²C configuration
See - Microchip PIC18F4550 datasheet (ch. 19)
- Microchip C18 library
SSPADD = 118;
OpenI2C(MASTER,SLEW_ON);
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configure I²C peripheral
(Master and 400 kHz mode)

19. initialization : 1 meter and result in centimeter
Measurement request
Waiting for 10 ms
Read result
4.3 Using telemeter by polling
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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

20. 4.4 Interrupts
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4.4 Interrupts

21. 4.5 Interrupts
What is an interrupt ?
Measurement request
Waiting for 10 ms
Read result
initialization
main program
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measurement
request
CPU
occupation
CPU is reading
the value of the timer3
read
result
CPU is reading
the value of the timer3
measurement
request
read
result
…

22. 4.5 Interrupts
What is an interrupt ?
initialization
Measurement request
Read result
main program interrupt subroutine
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measurement
request
CPU
occupation
read
result
measurement
request
read
result
…the CPU is free the CPU is free

23. 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
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- 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)

24. Peripheral Interrupt Enable registers (PIE1 and PIE2).
PIE1 = 0b00000000;
SPPIE ADIE TXIE TMR2IE TMR1IESSPIERCIE CCP1IE
4.5 Interrupts
interrupt in Microchip PIC18Fxxxx
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PIE2 = 0b00000010;
OSCFIE CMIE EEIE TMR3IE CCP2IEBCLIE
SPPIE ADIE TXIE TMR2IE TMR1IESSPIERCIE CCP1IE
USBIE HLVDIE

25. Peripheral Interrupt Request (Flag) registers (PIR1 and PIR2).
PIR1 = 0b00000000;
SPPIF ADIF TXIF TMR2IF TMR1IFSSPIFRCIF CCP1IF
interrupt in Microchip PIC18Fxxxx
4.5 Interrupts
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PIR2 = 0b00000000;
OSCFIF CMIF EEIF TMR3IF CCP2IFBCLIF
SPPIF ADIF TXIF TMR2IF TMR1IFSSPIFRCIF CCP1IF
USBIF HLVDIF

26. What happens when an interrupt occurs ?
interrupt in Microchip PIC18Fxxxx
4.5 Interrupts
The program executes the instruction
which is at the address 0x08 in the
program memory
Program
counter goto Interrupt funct
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main program
Interrupt function
Program
counterProgram
counter
Program
counter
Program
counter
Program
counter

27. 4.5 Using the telemeter with interrupts
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28. Flow chart
initialization
Measurement request
Read result
main program interrupt subroutine
4.5 Using the telemeter with interrupts
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measurement
request
CPU
occupation
read
result
measurement
request
read
result
…the CPU is free the CPU is free

29. 4.5 Using the telemeter with interrupts
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
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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

30. 4.5 Using the telemeter with interrupts
Interrupt subroutine
6th : 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
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)// 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 next
code is at the adress 0x08
it indicates that the next
code is in the program memory
_asm and _endasm frame
an asm instruction
on the interrupt