Electronics- Serial Communication-I2Cdenethor.wlu.ca/pc320/lectures/i2cbeam.pdfRaspberry Pi Python...

Serial Communication -I2CRaspberry Pi Python I2C Library

ElectronicsSerial Communication-I2C

Terry Sturtevant

Wilfrid Laurier University

February 13, 2019

Terry Sturtevant Electronics Serial Communication-I2C


Serial Communication -I2C

Inter-Integrated Circuit InterfaceMaster/slave communicationUses 2 signals (and Ground),SDA and SCLMany slaves can be on the same bus since each has an addressDevice addresses are pre-programmed, but can usually bechangedSynchronous, so master controls clock rate




Inter-Integrated Circuit Interface

Master/slave communicationUses 2 signals (and Ground),SDA and SCLMany slaves can be on the same bus since each has an addressDevice addresses are pre-programmed, but can usually bechangedSynchronous, so master controls clock rate




Inter-Integrated Circuit InterfaceMaster/slave communication

Uses 2 signals (and Ground),SDA and SCLMany slaves can be on the same bus since each has an addressDevice addresses are pre-programmed, but can usually bechangedSynchronous, so master controls clock rate




Inter-Integrated Circuit InterfaceMaster/slave communicationUses 2 signals (and Ground),SDA and SCL

Many slaves can be on the same bus since each has an addressDevice addresses are pre-programmed, but can usually bechangedSynchronous, so master controls clock rate




Inter-Integrated Circuit InterfaceMaster/slave communicationUses 2 signals (and Ground),SDA and SCLMany slaves can be on the same bus since each has an address

Device addresses are pre-programmed, but can usually bechangedSynchronous, so master controls clock rate




Inter-Integrated Circuit InterfaceMaster/slave communicationUses 2 signals (and Ground),SDA and SCLMany slaves can be on the same bus since each has an addressDevice addresses are pre-programmed, but can usually bechanged

Synchronous, so master controls clock rate




Inter-Integrated Circuit InterfaceMaster/slave communicationUses 2 signals (and Ground),SDA and SCLMany slaves can be on the same bus since each has an addressDevice addresses are pre-programmed, but can usually bechangedSynchronous, so master controls clock rate



Bidirectional Communication on a Single Line

How can multiple devices communicate on the same line?Each device has an open-collector (or open-drain) output.A pull-up resistor on the line allows it to go high whennothing is pulling it low.Any device which is not speaking must let their output float.Only one device can pull the line low at a time.

On the Raspberry Pi board, there are 1.8kΩ pull-up resistorsto 3.3V, so external ones are not normally required.




How can multiple devices communicate on the same line?

Each device has an open-collector (or open-drain) output.A pull-up resistor on the line allows it to go high whennothing is pulling it low.Any device which is not speaking must let their output float.Only one device can pull the line low at a time.





How can multiple devices communicate on the same line?Each device has an open-collector (or open-drain) output.

A pull-up resistor on the line allows it to go high whennothing is pulling it low.Any device which is not speaking must let their output float.Only one device can pull the line low at a time.





How can multiple devices communicate on the same line?Each device has an open-collector (or open-drain) output.A pull-up resistor on the line allows it to go high whennothing is pulling it low.

Any device which is not speaking must let their output float.Only one device can pull the line low at a time.





How can multiple devices communicate on the same line?Each device has an open-collector (or open-drain) output.A pull-up resistor on the line allows it to go high whennothing is pulling it low.Any device which is not speaking must let their output float.

Only one device can pull the line low at a time.





How can multiple devices communicate on the same line?Each device has an open-collector (or open-drain) output.A pull-up resistor on the line allows it to go high whennothing is pulling it low.Any device which is not speaking must let their output float.Only one device can pull the line low at a time.




Mixing devices with different supply voltages

Do you need optoisolators if devices require different supplyvoltages?

Each device has an open-collector (or open-drain) output.A pull-up resistor on the line allows it to go high whennothing is pulling it low.If the pull-up resistors only go to the lowest supply voltage,then the data line will never be too high.Since the Raspberry Pi has 1.8kΩ pull-up resistors to 3.3V,connecting to an I2C device with a 5V supply will not cause aproblem for the Pi.Note, however, if 3.3V inputs are not high enough for thedevice, then it might not operate correctly.





Each device has an open-collector (or open-drain) output.

A pull-up resistor on the line allows it to go high whennothing is pulling it low.If the pull-up resistors only go to the lowest supply voltage,then the data line will never be too high.Since the Raspberry Pi has 1.8kΩ pull-up resistors to 3.3V,connecting to an I2C device with a 5V supply will not cause aproblem for the Pi.Note, however, if 3.3V inputs are not high enough for thedevice, then it might not operate correctly.





Each device has an open-collector (or open-drain) output.A pull-up resistor on the line allows it to go high whennothing is pulling it low.

If the pull-up resistors only go to the lowest supply voltage,then the data line will never be too high.Since the Raspberry Pi has 1.8kΩ pull-up resistors to 3.3V,connecting to an I2C device with a 5V supply will not cause aproblem for the Pi.Note, however, if 3.3V inputs are not high enough for thedevice, then it might not operate correctly.





Each device has an open-collector (or open-drain) output.A pull-up resistor on the line allows it to go high whennothing is pulling it low.If the pull-up resistors only go to the lowest supply voltage,then the data line will never be too high.

Since the Raspberry Pi has 1.8kΩ pull-up resistors to 3.3V,connecting to an I2C device with a 5V supply will not cause aproblem for the Pi.Note, however, if 3.3V inputs are not high enough for thedevice, then it might not operate correctly.





Each device has an open-collector (or open-drain) output.A pull-up resistor on the line allows it to go high whennothing is pulling it low.If the pull-up resistors only go to the lowest supply voltage,then the data line will never be too high.Since the Raspberry Pi has 1.8kΩ pull-up resistors to 3.3V,connecting to an I2C device with a 5V supply will not cause aproblem for the Pi.

Note, however, if 3.3V inputs are not high enough for thedevice, then it might not operate correctly.





Each device has an open-collector (or open-drain) output.A pull-up resistor on the line allows it to go high whennothing is pulling it low.If the pull-up resistors only go to the lowest supply voltage,then the data line will never be too high.Since the Raspberry Pi has 1.8kΩ pull-up resistors to 3.3V,connecting to an I2C device with a 5V supply will not cause aproblem for the Pi.Note, however, if 3.3V inputs are not high enough for thedevice, then it might not operate correctly.



SDA



SDA

All floating; SDA is HIGH.Terry Sturtevant Electronics Serial Communication-I2C


SDA

One output LOW; SDA is LOW.Terry Sturtevant Electronics Serial Communication-I2C


SDA

SCL

START

MSB LSB ACK

STOP

I2C ; bits are read when SCL is HIGHACK is sent by receiver if OKsender must release SDA after LSB



SDA

SCL

START

MSB LSB NACK

STOP

I2C ; bits are read when SCL is HIGHNACK is sent by master-receiver if OKsender must release SDA after LSB



I2C write to slave register



START W

Slave address




START WA

Slave address




START WA

Slave addressRegister number




START WA A





START WA A


Register data




START WA A A


Register data




START STOPWA A

ASlave address

Register numberRegister data




I2C read from slave register



START W

Slave address




START WA

Slave address




START WA





START WA A





START WA A R


Slave address




START WA A RA


Slave address




START WA A RA


Slave addressRegister data




START WA A RA N






START STOPWA A RA

NSlave addressRegister number





Smbus

bus = smbus.SMBus(1)create objectbus.read i2c block data(addr,cmd)read from devicebus.write i2c block data(addr,cmd,vals)write to device



Smbus

bus = smbus.SMBus(1)create object

bus.read i2c block data(addr,cmd)read from devicebus.write i2c block data(addr,cmd,vals)write to device



Smbus

bus = smbus.SMBus(1)create objectbus.read i2c block data(addr,cmd)read from device

bus.write i2c block data(addr,cmd,vals)write to device



Smbus

bus = smbus.SMBus(1)create objectbus.read i2c block data(addr,cmd)read from devicebus.write i2c block data(addr,cmd,vals)write to device



Smbus

#!/ u s r / b i n / pythoni m p o r t smbusbus = smbus . SMBus ( 1 )DEVICE ADDRESS = 0 x15DEVICE REG MODE1 = 0 x00DEVICE REG LEDOUT0 = 0 x1d#Write a s i n g l e r e g i s t e rbus . w r i t e b y t e d a t a (DEVICE ADDRESS ,

DEVICE REG MODE1 , 0 x80 )

#Write an a r r a y o f r e g i s t e r sl e d o u t v a l u e s = [ 0 x f f , 0 x f f ,

0 x f f , 0 x f f , 0 x f f , 0 x f f ]bus . w r i t e i 2 c b l o c k d a t a (DEVICE ADDRESS ,

DEVICE REG LEDOUT0 , l e d o u t v a l u e s )



Smbus#!/ u s r / b i n / pythoni m p o r t smbusbus = smbus . SMBus ( 1 )DEVICE ADDRESS = 0 x15DEVICE REG MODE1 = 0 x00DEVICE REG LEDOUT0 = 0 x1d#Write a s i n g l e r e g i s t e rbus . w r i t e b y t e d a t a (DEVICE ADDRESS ,

DEVICE REG MODE1 , 0 x80 )

#Write an a r r a y o f r e g i s t e r sl e d o u t v a l u e s = [ 0 x f f , 0 x f f ,

0 x f f , 0 x f f , 0 x f f , 0 x f f ]bus . w r i t e i 2 c b l o c k d a t a (DEVICE ADDRESS ,

DEVICE REG LEDOUT0 , l e d o u t v a l u e s )


Electronics- Serial Communication-I2Cdenethor.wlu.ca/pc320/lectures/i2cbeam.pdfRaspberry Pi Python...

Documents

Transcript of Electronics- Serial Communication-I2Cdenethor.wlu.ca/pc320/lectures/i2cbeam.pdfRaspberry Pi Python...