lecture7-serial-spi-and-i2c in the means of communication

lecture7-serial-spi-and-i2c in the means of communication

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  Wireless Embedded Systems AaronSchulman Lecture 7 SPI and I2C
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  2 SPI Communication
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  3 SPI clocking: thereis no “standard way” • Four clocking “modes” – Two phases – Two polarities • Master and selected slave must be in the same mode • During transfers with slaves A and B, Master must – Configure clock to Slave A’s clock mode – Select Slave A – Do transfer – Deselect Slave A – Configure clock to Slave B’s clock mode – Select Slave B – Do transfer – Deselect Slave B • Master reconfigures clock mode on-the-fly!
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  4 SPI timing diagram TimingDiagram – Showing Clock polarities and phases http://www.maxim-ic.com.cn/images/appnotes/3078/3078Fig02.gif
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  SPI Modes: •Mode 0: •CPOL= 0 (Clock Idle Low) •CPHA = 0 (Data sampled on the rising edge) •Mode 1: •CPOL = 0 (Clock Idle Low) •CPHA = 1 (Data sampled on the falling edge) •Mode 2: •CPOL = 1 (Clock Idle High) •CPHA = 0 (Data sampled on the rising edge) •Mode 3: •CPOL = 1 (Clock Idle High) •CPHA = 1 (Data sampled on the falling edge) Key SPI Terms: •CPOL (Clock Polarity): Determines the idle state of the clock signal (high or low). •CPHA (Clock Phase): Determines when data is sampled (on the rising or falling edge of the clock). •SCK (Serial Clock): The clock signal that synchronizes data transfer between master and slave. •MOSI (Master Out Slave In): Data output from the master to the slave. •MISO (Master In Slave Out): Data input from the slave to the
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  6 SPI Pros andCons • Pros: – Fast and easy • Fast for point-to-point connections • Easily allows streaming/Constant data inflow • No addressing/Simple to implement – Everyone supports it • Cons: – SS makes multiple slaves very complicated – No acknowledgement ability – No inherent arbitration – No flow control
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  1. Interfacing withSensors and Peripherals: •Sensors: SPI is commonly used to interface with various sensors, including accelerometers, gyroscopes, temperature sensors, and other sensor modules, allowing microcontrollers to read data from these devices. •Displays: SPI facilitates communication with display interfaces, such as TFT LCDs and OLEDs, enabling microcontrollers to control the display's content and functionality. •Memory Devices: SPI is used for communication with memory devices like EEPROMs, flash memory, and SD cards, enabling data storage and retrieval. •Networking Peripherals: SPI can be used for communication with networking peripherals like Ethernet controllers and Wi-Fi modules, enabling microcontrollers to access network functionalities. 2. Communication between Microcontrollers and Peripheral Devices: •Master-Slave Architecture: SPI uses a master-slave architecture, where a master device (usually a microcontroller) initiates and controls the communication, and a slave device (e.g., a sensor, display, or memory chip) responds to the master's commands. •High-Speed Data Transfer: SPI allows for high-speed data transfer between microcontrollers and peripheral devices, making it suitable for applications requiring rapid data exchange. •Simplicity and Cost-Effectiveness: SPI is known for its simplicity and cost-effectiveness, making it a popular choice for embedded systems and IoT applications. 3. Specific Applications: •Industrial Control Systems: SPI is used in industrial control systems for communication between programmable logic controllers (PLCs), sensors, actuators, and other control devices. •RFID Card Readers: SPI is used in RFID card reader modules to communicate with microcontrollers. •Wireless Transmitters and Receivers: SPI is used in 2.4GHz wireless transmitters and receivers to communicate with microcontrollers. •Video Doorbell: SPI is used in video doorbell applications.
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  I2C bus (inour projects) • Communication with the accelerometer – Read acceleration values and configure interrupts • Pros – Two wires bus that can connect multiple peripherals with the MCU • Cons – Overhead is significantly higher, and bus is slower
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  I2C Details • Twolines – Serial data line (SDA) – Serial clock line (SCL) • Only two wires for connecting multiple devices
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  I2C Details • EachI2C device recognized by a unique address • Each I2C device can be either a transmitter or receiver • I2C devices can be masters or slaves for a data transfer – Master (usually a microcontroller): Initiates a data transfer on the bus, generates the clock signals to permit that transfer, and terminates the transfer – Slave: Any device addressed by the master at that time
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  How can anydevice transfer or receive on the same two wires? • Pull ups and high-impedance mode pins – Wires default to being “on”, any device can make a wire go “off”. – This is super clever. SPI and UART can’t do this, why?
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  12 of 40 BitTransfer on the I2 C Bus • In normal data transfer, the data line only changes state when the clock is low SDA SCL Data line stable; Data valid Change of data allowed
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  13 of 40 Startand Stop Conditions • A transition of the data line while the clock line is high is defined as either a start or a stop condition. • Both start and stop conditions are generated by the bus master • The bus is considered busy after a start condition, until a stop condition occurs Start Condition Stop Condition SCL SCL SDA SDA
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  14 of 40 I2 CAddressing • Each node has a unique 7 (or 10) bit address • Peripherals often have fixed and programmable address portions • Addresses starting with 0000 or 1111 have special functions:- – 0000000 Is a General Call Address – 0000001 Is a Null (CBUS) Address – 1111XXX Address Extension – 1111111 Address Extension – Next Bytes are the Actual Address
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  I2C-Connected System Example I2C-connectedsystem with two microcontrollers (Source: I2C Specification, Philips)
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  Master-Slave Relationships • Whois the master? – master-transmitters – master-receivers • Suppose microcontroller A wants to send information to microcontroller B – A (master) addresses B (slave) – A (master-transmitter), sends data to B (slave-receiver) – A terminates the transfer. • If microcontroller A wants to receive information from microcontroller B – A (master) addresses microcontroller B (slave) – A (master-receiver) receives data from B (slave-transmitter) – A terminates the transfer • In both cases, the master (microcontroller A) generates the timing and terminates the transfer
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  Exercise: How fastcan I2C run? 17 • How fast can you run it? • Assumptions – 0’s are driven – 1’s are “pulled up” • Some working figures – Rp = 10 kΩ – Ccap = 100 pF – VDD = 5 V – Vin_high = 3.5 V • Recall for RC circuit – Vcap(t) = VDD(1-e-t/τ ) – Where τ = RC
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  Exercise: Bus bitrate vs Useful data rate 18 • An I2C “transactions” involves the following bits – <S><A6:A0><R/W><A><D7:D0><A><F> • Which of these actually carries useful data? – <S><A6:A0><R/W><A><D7:D0><A><F> • So, if a bus runs at 400 kHz – What is the clock period? – What is the data throughput (i.e. data-bits/second)? – What is the bus “efficiency”?
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  How to operatethe accelerometer? MCU Accel I2C I2C register 1 register 2 …. Springs https://www.youtube.com/watch?v=eqZgxR6eRjo