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March 2021 ). Typical applications include Secure Digital cards and liquid crystal displays. The master device originates the frame for reading and writing. Multiple slave-devices are supported through selection with individual slave select (SS), sometimes called chip select (CS), lines. N64 Controller Serial Protocol Interface Serial Communication ProtocolThe SPI may be accurately described as a synchronous serial interface, 1 but it is different from the Synchronous Serial Interface (SSI) protocol, which is also a four-wire synchronous serial communication protocol. The SSI protocol employs differential signaling and provides only a single simplex communication channel. Slave Select has the same functionality as chip select and is used instead of an addressing concept. Pin names are always capitalized e.g. Slave Select, not slave select. Some slaves require a falling edge of the chip select signal to initiate an action. An example is the Maxim MAX1242 ADC, which starts conversion on a highlow transition. With multiple slave devices, an independent SS signal is required from the master for each slave device. Devices without tri-state outputs cannot share SPI bus segments with other devices without using an external tri-state buffer. The master then selects the slave device with a logic level 0 on the select line. If a waiting period is required, such as for an analog-to-digital conversion, the master must wait for at least that period of time before issuing clock cycles. The master sends a bit on the MOSI line and the slave reads it, while the slave sends a bit on the MISO line and the master reads it. This sequence is maintained even when only one-directional data transfer is intended. Data is usually shifted out with the most significant bit first. On the clock edge, both master and slave shift out a bit and output it on the transmission line to the counterpart. On the next clock edge, at each receiver the bit is sampled from the transmission line and set as a new least-significant bit of the shift register. After the register bits have been shifted out and in, the master and slave have exchanged register values. ![]() When complete, the master stops toggling the clock signal, and typically deselects the slave. However, other word-sizes are also common, for example, sixteen-bit words for touch-screen controllers or audio codecs, such as the TSC2101 by Texas Instruments, or twelve-bit words for many digital-to-analog or analog-to-digital converters. Multiple SPI devices may also be daisy-chained to conserve pins.
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