1. Serial Communication Buses: I2C and SPI
By Brody Dunn

2. Goals Revisit Readings of I2C and SPI Not Insult You
Realize Level of Understanding
Take Next Step
Implementation

3. Inter-Integrated Circuit (I2C)
2-Wire Serial Communication Bus
Introduced By Philips In 1992
Communication Protocol Between Microcontroller And Peripherals
Real Time Clocks (RTCs)
Analog to Digital Converters (ADCs)
Various Sensors
Many, many, more

4. I2C Characteristics Only 2 Wires Needed On Bus
Serial Data (SDA)
Serial Clock (SCL)
Multiple Devices Connected On Bus
Typically Limited (i.e. 8, 20, 27, 210,...?)
Similar Code For All I2C Peripherals
Supports Various Data Transfer Rates

5. Development of I2C Version 1.0 Introduced in 1992
“Standard” 100 Kbits/s
“Fast” 400 Kbits/s
Version 2.0 Released in 1998
“High-Speed” 3.4 Mbits/s
Version 2.1 Released in 2000
Clock Stretched
“High-Speed” Timings Relaxed

6. How Does It Work?

7. Further Reading I2C-Bus Specification Version 2.1 DS1631 Datasheet
DS1631 Datasheet

8. Serial Peripheral Interface (SPI)
Synchronous Communication Protocol
3-Wire (Plus 1 Chip-Select Pin/Device)
Hardware On Microcontroller
Developed By Motorola
“Loose” Standard
Broad Range of Devices Supported
Memory (i.e. EEPROM, RAM, Etc.)
Sensors

9. SPI Characteristics 3 Wires (Plus Chip Select Pin/Device)
Master Out Slave In (MOSI)
Master In Slave Out (MISO)
Master/Slave Clock Output/Input (SCK)
Chip/Slave Select (SS)
Multiple Devices Connected On Bus
Limited Only By Number Of uC Pins
Supports Various Data Transfer Rates

10. How Does It Work?

11. Configurations (AT89S53) SPI Control Register (SPCR)
Sets Modes of Operation
SPI Status Register (SPSR)
Checks Flags
SPI Data Register (SPDR)
8-Bit Shift Register Storing Data

12. 4 Modes of SPI Set In SPI Control Register (SPCR) Clock Polarity
Active Low
Active High
Clock Phase
Data Shifted On Rising Edge
Data Shifted On Falling Edge

13. 4 Modes of SPI (CPHA = 0)

14. 4 Modes of SPI (CPHA = 1)

15. Further Reading AT89S53 Datasheet (Pg. 8, 14-16) Pont Ch. 24
Pont Ch. 24

16. SPI Summary 3-Wire (+ SS/Device) 1.5 MHz Bit Frequency (AT89S53)
Microcontroller Hardware
Supports Many Devices