Peripherals
4.7
Serial Peripheral Interface (SPI) Module
The F281x and C281x devices include the four-pin serial peripheral interface (SPI) module. The SPI is a
high-speed, synchronous serial I/O port that allows a serial bit stream of programmed length (one to sixteen
bits) to be shifted into and out of the device at a programmable bit-transfer rate. Normally, the SPI is used for
communications between the DSP controller and external peripherals or another processor. Typical
applications include external I/O or peripheral expansion through devices such as shift registers, display
drivers, and ADCs. Multidevice communications are supported by the master/slave operation of the SPI.
The SPI module features include:
•
Four external pins:
−
−
−
−
SPISOMI: SPI slave-output/master-input pin
SPISIMO: SPI slave-input/master-output pin
SPISTE: SPI slave transmit-enable pin
SPICLK: SPI serial-clock pin
NOTE: All four pins can be used as GPIO, if the SPI module is not used.
•
•
Two operational modes: master and slave
Baud rate: 125 different programmable rates
LSPCLK
−
Baud rate =
, when BRR ≠ 0
(SPIBRR ) 1)
LSPCLK
=
,
when BRR = 0, 1, 2, 3
4
Serial port performance is limited by I/O buffer switching speed. Internal prescalers must be adjusted
such that the peripheral speed is less than the I/O buffer speed limit—20 MHz maximum.
•
•
Data word length: one to sixteen data bits
Four clocking schemes (controlled by clock polarity and clock phase bits) include:
−
−
−
−
Falling edge without phase delay: SPICLK active-high. SPI transmits data on the falling edge of the
SPICLK signal and receives data on the rising edge of the SPICLK signal.
Falling edge with phase delay: SPICLK active-high. SPI transmits data one half-cycle ahead of the
falling edge of the SPICLK signal and receives data on the falling edge of the SPICLK signal.
Rising edge without phase delay: SPICLK inactive-low. SPI transmits data on the rising edge of the
SPICLK signal and receives data on the falling edge of the SPICLK signal.
Rising edge with phase delay: SPICLK inactive-low. SPI transmits data one half-cycle ahead of the
falling edge of the SPICLK signal and receives data on the rising edge of the SPICLK signal.
•
•
Simultaneous receive and transmit operation (transmit function can be disabled in software)
Transmitter and receiver operations are accomplished through either interrupt-driven or polled
algorithms.
•
Nine SPI module control registers: Located in control register frame beginning at address 7040h.
NOTE: All registers in this module are 16-bit registers that are connected to Peripheral Frame 2. When a
register is accessed, the register data is in the lower byte (7−0), and the upper byte (15−8) is read as
zeros. Writing to the upper byte has no effect.
Enhanced feature:
•
•
16-level transmit/receive FIFO
Delayed transmit control
80
SPRS174L
April 2001 − Revised December 2004
TI [ TEXAS INSTRUMENTS ]
