SPI Modes with CPOL and CPHA SPI ModeĬlock Phase Used to Sample and/or Shift the Dataĭata sampled on rising edge and shifted out on the falling edgeĭata sampled on the falling edge and shifted out on the rising edgeĭata sampled on the rising edge and shifted out on the falling edgeįigure 2 through Figure 5 show an example of communication in four SPI modes. Depending on the CPOL and CPHA bit selection, four SPI modes are available. The master must select the clock polarity and clock phase, as per the requirement of the slave. Depending on the CPHA bit, the rising or falling clock edge is used to sample and/or shift the data. The idle state is defined as the period when CS is high and transitioning to low at the start of the transmission and when CS is low and transitioning to high at the end of the transmission.
The CPOL bit sets the polarity of the clock signal during the idle state. In SPI, the master can select the clock polarity and clock phase. Please refer to the device data sheet to determine the number of data bits transmitted using the SPI interface. The SPI interface provides the user with flexibility to select the rising or falling edge of the clock to sample and/or shift the data. The serial clock edge synchronizes the shifting and sampling of the data. During SPI communication, the data is simultaneously transmitted (shifted out serially onto the MOSI/SDO bus) and received (the data on the bus (MISO/SDI) is sampled or read in). SPI is a full-duplex interface both master and slave can send data at the same time via the MOSI and MISO lines respectively. To begin SPI communication, the master must send the clock signal and select the slave by enabling the CS signal. Usually chip select is an active low signal hence, the master must send a logic 0 on this signal to select the slave. MOSI transmits data from the master to the slave and MISO transmits data from the slave to the master. In this article, the chip select signal is always an active low signal. When multiple slaves are used, an individual chip select signal for each slave is required from the master. This is normally an active low signal and is pulled high to disconnect the slave from the SPI bus. The chip select signal from the master is used to select the slave. Figure 1 shows the SPI connection between the master and the slave.
SPI interfaces can have only one master and can have one or multiple slaves. Users should consult the product data sheet for the clock frequency specification of the SPI interface. SPI devices support much higher clock frequencies compared to I 2C interfaces. Data transmitted between the master and the slave is synchronized to the clock generated by the master. The device that generates the clock signal is called the master. SPI configuration with master and a slave. This article focuses on the popular 4-wire SPI interface. The SPI interface can be either 3-wire or 4-wire. Both master and slave can transmit data at the same time. The data from the master or the slave is synchronized on the rising or falling clock edge.
#SPI AND SERIAL COMMUNICATION BASICS FULL#
SPI is a synchronous, full duplex master-slave-based interface. This article provides a brief description of the SPI interface followed by an introduction to Analog Devices’ SPI enabled switches and muxes, and how they help reduce the number of digital GPIOs in system board design. Serial peripheral interface (SPI) is one of the most widely used interfaces between microcontroller and peripheral ICs such as sensors, ADCs, DACs, shift registers, SRAM, and others.
0 kommentar(er)
