AT32UC3C1512C Automotive Atmel Corporation, AT32UC3C1512C Automotive Datasheet - Page 595

• Manufacturer Part Number: AT32UC3C1512C Automotive
• Manufacturer: Atmel Corporation

25.6.8
25.6.8.1
9166C–AVR-08/11
SPI Mode
Modes of Operation
The Serial Peripheral Interface (SPI) Mode is a synchronous serial data link that provides com-
munication with external devices in Master or Slave Mode. It also enables communication
between processors if an external processor is connected to the system.
The Serial Peripheral Interface is essentially a shift register that serially transmits data bits to
other SPIs. During a data transfer, one SPI system acts as the “master” which controls the data
flow, while the other devices act as “slaves'' which have data shifted into and out by the master.
Different CPUs can take turns being masters and one master may simultaneously shift data into
multiple slaves. (Multiple Master Protocol is the opposite of Single Master Protocol, where one
CPU is always the master while all of the others are always slaves.) However, only one slave
may drive its output to write data back to the master at any given time.
A slave device is selected when its NSS signal is asserted by the master. The USART in SPI
Master mode can address only one SPI Slave because it can generate only one NSS signal.
Nevertheless the user can use standard I/O lines to access more than one SPI slave.
The SPI system consists of two data lines and two control lines:
The USART can operate in Master Mode or in Slave Mode.
Operation in SPI Master Mode is programmed by writing at 0xE the MODE field in the Mode
Register. In this case the SPI lines must be connected as described below:
Operation in SPI Slave Mode is programmed by writing at 0xF the MODE field in the Mode Reg-
ister. In this case the SPI lines must be connected as described below:
In order to avoid unpredicted behavior, any change of the SPI Mode must be followed by a soft-
ware reset of the transmitter and of the receiver (except the initial configuration after a hardware
reset).
• Master Out Slave In (MOSI): This data line supplies the output data from the master shifted
• Master In Slave Out (MISO): This data line supplies the output data from a slave to the input
• Serial Clock (CLK): This control line is driven by the master and regulates the flow of the data
• Slave Select (NSS): This control line allows the master to select or deselect the slave.
• the MOSI line is driven by the output pin TXD
• the MISO line drives the input pin RXD
• the CLK line is driven by the output pin CLK
• the NSS line is driven by the output pin RTS
• the MOSI line drives the input pin RXD
• the MISO line is driven by the output pin TXD
• the CLK line drives the input pin CLK
• the NSS line drives the input pin CTS
into the input of the slave.
of the master.
bits. The master may transmit data at a variety of baud rates. The CLK line cycles once for
each bit that is transmitted.
AT32UC3C
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