2021-11-20 23:45:01 +00:00
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= SPI =
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SPI or Serial peripheral interface is the standard often used as a form of
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interchip communication on boards, and in embedded devices.
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See https://www.youtube.com/watch?v=MCi7dCBhVpQ
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== Layout ==
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Each device, the master and slave (often microcontroler as master and
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peripheral/sensor as slave) have four pins
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* SCK - Serial Clock
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* CS - Chip select (active low)
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* SDI - Serial data in
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* SDO - Serial data out
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NOTE serial data * is from the persepctive of the device (SDI on master is
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connected to SDO on slave and vice versa).
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SDO on the master to SDI on the peripherial is often called MOSI (Master out
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Slave in), and the inverse is often called MISO (Master in Slave out).
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Some chips may only have a MOSI, as some devices do not create data to send
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back to the master.
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== Sending data ==
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On the *rising edge* of the clock, each device reads what is currently set on
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the respective input port. The chip must also have its output set before the
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rising edge, to ensure that the device will receive the data it intends to
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2021-11-21 00:00:01 +00:00
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send. All of this only occurs when CS is set low. This is known as *mode 0*
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Ther are several other modes. All of the modes are detailed in the table below.
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| Mode | CLK default | Send on | Sample on |
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--------------------------------------------
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| 0 | LOW | falling edge | rising edge |
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| 1 | LOW | rising edge | falling edge |
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| 2 | HIGH | rising edge | falling edge |
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| 3 | HIGH | falling edge | rising edge |
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