Serial Communication Buses: I2C and SPIBy Brody Dunn

GoalsRevisit Readings of I2C and SPINot Insult YouRealize Level of UnderstandingTake Next StepImplementation

Inter-Integrated Circuit (I2C)2-Wire Serial Communication BusIntroduced By Philips In 1992Communication Protocol Between Microcontroller And PeripheralsReal Time Clocks (RTCs)Analog to Digital Converters (ADCs)Various SensorsMany, many, more

I2C CharacteristicsOnly 2 Wires Needed On BusSerial Data (SDA)Serial Clock (SCL)Multiple Devices Connected On BusTypically Limited (i.e. 8, 20, 27, 210,...?)Similar Code For All I2C PeripheralsSupports Various Data Transfer Rates

Development of I2CVersion 1.0 Introduced in 1992Standard 100 Kbits/sFast 400 Kbits/sVersion 2.0 Released in 1998High-Speed 3.4 Mbits/sVersion 2.1 Released in 2000Clock StretchedHigh-Speed Timings Relaxed

How Does It Work?

Further ReadingI2C-Bus Specification Version 2.1http://www.semiconductors.philips.com/acrobat_download/literature/9398/39340011.pdfDS1631 Datasheethttp://pdfserv.maxim-ic.com/en/ds/DS1631-DS1731.pdf

Serial Peripheral Interface (SPI)Synchronous Communication Protocol3-Wire (Plus 1 Chip-Select Pin/Device)Hardware On MicrocontrollerDeveloped By Motorola Loose StandardBroad Range of Devices SupportedMemory (i.e. EEPROM, RAM, Etc.)Sensors

SPI Characteristics3 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 BusLimited Only By Number Of uC PinsSupports Various Data Transfer Rates

How Does It Work?

Configurations (AT89S53)SPI Control Register (SPCR)Sets Modes of OperationSPI Status Register (SPSR)Checks FlagsSPI Data Register (SPDR)8-Bit Shift Register Storing Data

4 Modes of SPISet In SPI Control Register (SPCR)Clock PolarityActive LowActive HighClock PhaseData Shifted On Rising EdgeData Shifted On Falling Edge

4 Modes of SPI (CPHA = 0)

4 Modes of SPI (CPHA = 1)

Further ReadingAT89S53 Datasheet (Pg. 8, 14-16) http://www.atmel.com/dyn/resources/prod_documents/DOC0787.PDFPont Ch. 24

SPI Summary3-Wire (+ SS/Device)1.5 MHz Bit Frequency (AT89S53)Microcontroller HardwareSupports Many Devices