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<concept id="GUID-99FC067C-0AED-5373-AF63-8DB7FF5C1F7E" xml:lang="en"><title>SPI Technology Guide</title><shortdesc>This document describes the Serial Peripheral Interface

(SPI) technology. The SPI devices are used for fast data exchange

between two or more peripherals. </shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

<section id="GUID-B3154A94-3117-5427-BAAD-C402F41AF217"><title>Introduction</title> <p>The SPI is a synchronous serial interface. The SPI supports full

duplex communication channel for the devices that use SPI interface.

The devices and peripherals that use the SPI interface are described

as SPI devices in this document. </p> </section>

<section id="GUID-6FAE8B3E-904C-567B-A6CC-5558D417BA66"><title>Architecture</title> <p>In the SPI bus one of the node must be a master device and one

or more slave devices. There can be only one slave active at a time.

The master device initiates and terminates communication between the

SPI devices. The SPI is a full duplex serial data communication. In

full duplex communication the data can be transferred between the

master and the slave devices simultaneously. </p> <p>The SPI devices

can be configured as master or slave. The SPI bus contain four wires.

The first one is the serial clock signal sent by the master device

to the slave device. The clock signal is used for synchronisation.

The Master Output / Slave Input (<codeph>MOSI</codeph>) is used to

send data from the master to the slave. The Slave Output / Master

Input (<codeph>SOMI</codeph>) is used by the master device to read

data from the slave device. The fourth line is the Slave Select (<codeph>SS</codeph>) that is used by the master to select a slave to initiate

the communication. </p> <fig id="GUID-E7B96ED2-9814-5B75-8051-48337121F985-GENID-1-2-1-10-1-5-1-6-1-1-6-1-5-1-3-2-4">

<title>              SPI Bus            </title>

<image href="GUID-2AE438CC-F2E4-5FCB-971F-CFFAE5EF81E4_d0e93636_href.png" placement="inline"/>

</fig> </section>

<section id="GUID-6931A479-BF67-4BF7-8593-712D1770B402"><title>Communication</title> <p>The master device is the node on the SPI bus that initiates and

terminates the communication. The master must provide the configuration

to the slave devices. The configuration includes the details like

the channel number and the data length. The SPI devices uses 4 and

8 bit words to communicate. If a slave device or a channel is not

available the appropriate error is returned to the master. </p> </section>

<section id="GUID-B9575A06-1A72-529D-9023-FAC1ED895A34"><title>Advantages</title> <p>The following are the advantages of the SPI interface: </p> <ul>

<li id="GUID-5FFFECEF-BCEA-5A8A-83F1-52E24019B22C"><p>Full duplex

synchronous communication </p> </li>

<li id="GUID-358181F9-4831-582F-B6F3-06AD09724BCB"><p>Low power requirements

compared to the I2C devices </p> </li>

<li id="GUID-701BDE22-3306-55EC-96FF-4E8F241CFFD6"><p>Less space compared

to the parallel bus </p> </li>

<li id="GUID-97E797F6-9228-58AA-984A-D872CCFDD812"><p>Slave devices

do not require unique address assigned </p> </li>

</ul> </section>

<section id="GUID-8EF6A8EA-E813-5EF9-AE61-9ACD7FF8625E"><title>SPI

devices</title> <p>Typically the SPI devices are used for data transfers

where a delay in the time taken to send the data is acceptable. The

clients of the SPI interface are device drivers running on the application

specific integrated circuits (ASIC). Some of the peripherals that

use SPI interface are: </p> <ul>

<li id="GUID-D72EE2AE-A335-53FA-8A5E-DB110D4DDB2A"><p>Touch screens </p> </li>

<li id="GUID-E60C872B-5B0B-5973-81FA-F93585859037"><p>Codecs </p> </li>

<li id="GUID-4332DFC4-A2BF-5533-8704-6F56EF76C161"><p>Real Time Clocks </p> </li>

<li id="GUID-DDFD3CB6-9696-504C-B23F-698873FA075E"><p>Built-in cameras </p> </li>

<li id="GUID-DA624D60-DEDD-56F0-BC77-13FCBDB0D959"><p>Flash memory

like MMC and SD cards </p> </li>

</ul> </section>

</conbody><related-links>

<link href="GUID-B2F86F54-EF50-56DB-ADF7-15325AC9324D.dita"><linktext>IIC

Concepts</linktext></link>

</related-links></concept>