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The Serial Peripheral Interface or SPI-bus is
a 4-wire serial communications interface used by many microprocessor
peripheral chips operating at full-duplex. The Serial Peripheral
Interface (SPI) circuit is a synchronous serial data link [1 megabaud]
setup as a Master / Slave interface, operating as a full-duplexed
protocol.
The SPI bus can support up to 10Mbps. The SPI bus specifies two control
lines Chip Select [CS] and Serial ClocK [SCLK] and two data lines Serial
Data In [SDI] and Serial Data Out [SDO]. There may be other naming
conventions such as MOSI [Master-Out-Slave-In], MISO
[Master-In-Slave-Out], or SS [Slave-Select] that are used by Motorola.
Devices may not have or use all four of the I/O pins. SDI [MOSI] may not
be present if a device does not require an input [ADC for example], or
SDO [MISO] may not be present if a device does not require an output [LCD
controllers]. One SPI device acts as the SPI Master by controlling the
data flow [generating [SCLK] and asserting device select [CS], then
receives and or transmits data via the two data lines.
If the devices on the SPI bus have a chip-select signal it is possible to
connect many ICs to the same SPI bus in parallel. If there is a
chip-select (CS) signal in use, it can be driven by a spare microcontroller general-purpose
output. Every IC connected to the bus needs it's own chip-select signal
line. The SCI bus which is used for Asynchronous Serial Communication may
be seen next to the SPI bus on a microprocessor.
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