Let us see examples of SPI as Master and SPI as Slave. Following is the diagrammatic representation of the connection between both the boards − Now, we will connect two Arduino UNO boards together one as a master and the other as a slave. SPI.attachInterrupt(handler) − Function to be called when a slave device receives data from the master. Mode 3 − Clock is normally high (CPOL = 1), and the data is sampled on the transition from low to high (trailing edge) (CPHA = 1). Mode 2 − Clock is normally high (CPOL = 1), and the data is sampled on the transition from high to low (leading edge) (CPHA = 0).
Mode 1 − Clock is normally low (CPOL = 0), and the data is sampled on the transition from high to low (trailing edge) (CPHA = 1). Mode 0 (the default) − Clock is normally low (CPOL = 0), and the data is sampled on the transition from low to high (leading edge) (CPHA = 0). We have four modes of operation in SPI as follows − SPI.beginTransaction(SPISettings(speedMaximum, dataOrder, dataMode)) − speedMaximum is the clock, dataOrder(MSBFIRST or LSBFIRST), dataMode(SPI_MODE0, SPI_MODE1, SPI_MODE2, or SPI_MODE3). SPI.transfer(val) − SPI transfer is based on a simultaneous send and receive: the received data is returned in receivedVal. The default setting is SPI_CLOCK_DIV4, which sets the SPI clock to one-quarter of the frequency of the system clock (5 Mhz for the boards at 20 MHz).ĭivider − It could be (SPI_CLOCK_DIV2, SPI_CLOCK_DIV4, SPI_CLOCK_DIV8, SPI_CLOCK_DIV16, SPI_CLOCK_DIV32, SPI_CLOCK_DIV64, SPI_CLOCK_DIV128). On AVR based boards, the dividers available are 2, 4, 8, 16, 32, 64 or 128. SPI.setClockDivider(divider) − To set the SPI clock divider relative to the system clock. SPI.begin() − Initializes the SPI bus by setting SCK, MOSI, and SS to outputs, pulling SCK and MOSI low, and SS high. MISO − This is the master input / slave output driven by the master. MOSI − This is the master output / slave input driven by the master. SCK − This is the serial clock driven by the master. The maximum baud rate is higher than that in the I2C communication system. It is a full duplex connection, which means that the data is sent and received simultaneously.
One conductor is used for data receiving, one for data sending, one for synchronization and one alternatively for selecting a device to communicate with. A Serial Peripheral Interface (SPI) bus is a system for serial communication, which uses up to four conductors, commonly three.
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