C once the selected ss is low one edge rising or

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c Once the selected SS is low, one edge (rising or falling) of the SCLK signals the devices (Master and Slave) to toggle the MOSI and MISO to the correct bit of data being transmitted. c The other edge of the SCLK line (rising or falling) signals the devices to register the bits on the MOSI and MISO, effectively reading the bit into the device.
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Basic Transmission Step-by-Step c The transmission continues in this fashion until the devices have exchanged the specified number of bits (usually 8,16, or 32) c After the transmission is complete the Master pulls the SS line for the slave back high and either goes to another slave on the network or reinitiates the transmission with the same slave by pulling the corresponding SS line back to low.
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Flowchart of the basic SPI transmission
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Daisy chain SPI configuration
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Daisy chain SPI configuration c The first slave output being connected to the second slave input, etc. c The SPI port of each slave is designed to send out during the second group of clock pulses an exact copy of what it received during the first group of clock pulses. c The whole chain acts as an SPI communication shift register; c Daisy chaining is often done with shift registers to provide a bank of inputs or outputs through SPI . c Such a feature only requires a single SS line from the master, rather than a separate SS line for each slave c Applications (discussed later) that require a daisy chain configuration include SGPIO and JTAG
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Strengths and Weaknesses of SPI Strengths c Widespread support and IP available c Full duplex communication c Higher throughput than I²C or SMBus c Complete protocol flexibility for the bits transferred (i.e. Not limited to 8-bit words) c Simple Protocol to implement and understand c Typically no external circuitry required (like pullup resistors for I²C) c System clocked by a master meaning that precision oscillators and PLL not needed c Addressing not needed (decreases complexity and helps throughput by not sending an address for each communication) c Transceivers are not needed c Serial protocol use fewer physical connections than parallel interfaces c Mostly shared lines for multiple devices (except the separate SS lines for each device)
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Strengths and Weaknesses of SPI Weaknesses c No standards body governs SPI as an official protocol c The more devices you have the more pins and connections necessary c No hardware flow control c No hardware slave acknowledgment (the master could be "talking" to nothing and not know it) c Does not support a multi-master architecture c Only handles relatively short distances (meant for on-PCB communication mostly)
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Applications SPI is used to talk to a variety of peripherals, such as: c Sensors: temperature, pressure, ADC, touchscreens c Control devices: audio codecs, digital potentiometers, DAC c Camera lenses: Canon EF lens mount c Communications: Ethernet, USB, USART, CAN, IEE 802.15.4, IEEE 802.11 c Memory: flash and EEPROM c Real-time clocks c LCD displays, sometimes even for managing image data c Any MMC or SD card (including SDIO variant)
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Reference : Application Note AN4024 from Maxim
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c Once the selected SS is low one edge rising or falling of...

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