![]() Second Slave Select – an additional control line that allows slaves to be turned on and off via hardware control. (This SS is in the same location as the SS line of the Aardvark and Beagle products.) Primary Slave Select – the primary control line that allows slaves to be turned on and off via hardware control. Master In Slave Out – this data line supplies the output data from the slave to the input of the master. Master Out Slave In – this data line supplies output data from the master which is shifted into the slave. Serial Clock – control line that is driven by the master and regulates the flow of the data bits. Two ground pins are provided to ensure a secure ground path. Without a common ground between the two, the signaling will be unpredictable and communication will likely be corrupted. It is imperative that the Cheetah adapter's ground lead is connected to the ground of the target system. Pin 1 is located in the lower left corner of the connector and Pin 10 is located in the upper right corner of the connector. These combinations are shown in figure 2.įigure 4 : The Cheetah SPI Host Adapter in the upside down position. Both parameters have two states which results in four possible combinations. The data frame is described by two parameters: clock polarity (CPOL) and clock phase (CPHA). 1.1.3 SPI ModesĪlthough there is no protocol, the master and slave need to agree about the data frame for the exchange. The flipside is that there is no acknowledgment, no flow control, and the master may not even be aware of the slaves presence. Data can be transferred at high speed, often into the range of the tens of megahertz. This makes it ideal for data-streaming applications. The exchange itself has no pre-defined protocol. The master pulls low on a slaves SS line to select a device for communication. Likewise, a device only interested in the incoming bytes can transmit dummy bytes.Įach device has its own SS line. Data is always transferred in both directions in SPI, but an SPI device interested in only transmitting data can choose to ignore the receive bytes. The direction of transfer is indicated by their names. SCLK is generated by the master device and is used for synchronization. Three signals are shared by all devices on the SPI bus: SCLK, MOSI and MISO. This means that as devices are added, the circuit increases in complexity. Each slave device requires a separate slave select signal (SS).
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