Serial Peripheral Interface (SPI)
13 - 4 C2000 Microcontroller Workshop - Communications
Serial Peripheral Interface (SPI)
The SPI module is a synchronous serial I/O port that shifts a serial bit stream of variable length
and data rate between the C28x and other peripheral devices. During data transfers, one SPI
device must be configured as the transfer MASTER, and all other devices configured as
SLAVES. The master drives the transfer clock signal for all SLAVES on the bus. SPI
communications can be implemented in any of three different modes:
• MASTER sends data, SLAVES send dummy data
• MASTER sends data, one SLAVE sends data
• MASTER sends dummy data, one SLAVE sends data
In its simplest form, the SPI can be thought of as a programmable shift register. Data is shifted in
and out of the SPI through the SPIDAT register. Data to be transmitted is written directly to the
SPIDAT register, and received data is latched into the SPIBUF register for reading by the CPU.
This allows for double-buffered receive operation, in that the CPU need not read the current
received data from SPIBUF before a new receive operation can be started. However, the CPU
must read SPIBUF before the new operation is complete of a receiver overrun error will occur. In
addition, double-buffered transmit is not supported: the current transmission must be complete
before the next data character is written to SPIDAT or the current transmission will be corrupted.
The Master can initiate a data transfer at any time because it controls the SPICLK signal. The
software, however, determines how the Master detects when the Slave is ready to broadcast.
SPI Data Flow
Simultaneous transmits and receive
SPI Master provides the clock signal
SPI Shift Register
SPI Device #1 - Master SPI Device #2 - Slave
shift
shift
clock
SPI Shift Register
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