406
32072H–AVR32–10/2012
AT32UC3A3
21.5
I/O Lines Description
21.6
Product Dependencies
In order to use this module, other parts of the system must be configured correctly, as described
below.
21.6.1
I/O Lines
The pins used for interfacing the compliant external devices may be multiplexed with I/O lines.
The user must first configure the I/O Controller to assign the SPI pins to their peripheral
functions.
21.6.2
Clocks
The clock for the SPI bus interface (CLK_SPI) is generated by the Power Manager. This clock is
enabled at reset, and can be disabled in the Power Manager. It is recommended to disable the
SPI before disabling the clock, to avoid freezing the SPI in an undefined state.
21.6.3
Interrupts
The SPI interrupt request line is connected to the interrupt controller. Using the SPI interrupt
requires the interrupt controller to be programmed first.
21.7
Functional Description
21.7.1
Modes of Operation
The SPI operates in master mode or in slave mode.
Operation in master mode is configured by writing a one to the Master/Slave Mode bit in the
Mode Register (MR.MSTR). The pins NPCS0 to NPCS3 are all configured as outputs, the SPCK
pin is driven, the MISO line is wired on the receiver input and the MOSI line driven as an output
by the transmitter.
If the MR.MSTR bit is written to zero, the SPI operates in slave mode. The MISO line is driven by
the transmitter output, the MOSI line is wired on the receiver input, the SPCK pin is driven by the
transmitter to synchronize the receiver. The NPCS0 pin becomes an input, and is used as a
Slave Select signal (NSS). The pins NPCS1 to NPCS3 are not driven and can be used for other
purposes.
The data transfers are identically programmable for both modes of operations. The baud rate
generator is activated only in master mode.
Table 21-1.
I/O Lines Description
Pin Name
Pin Description
Type
Master
Slave
MISO
Master In Slave Out
Input
Output
MOSI
Master Out Slave In
Output
Input
SPCK
Serial Clock
Output
Input
NPCS1-NPCS3
Peripheral Chip Selects
Output
Unused
NPCS0/NSS
Peripheral Chip Select/Slave Select
Output
Input