7 serial peripheral interface (spi) module – Texas Instruments Digital Signal Processor SM320F2812-HT User Manual
Page 74
LSPCLK
,
(SPIBRR 1)
+
LSPCLK
,
4
SGUS062B
–
JUNE 2009
–
REVISED JUNE 2011
4.7
Serial Peripheral Interface (SPI) Module
The F2812 device includes 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
–
Baud rate
when BRR
≠
0
=
=
when BRR = 0, 1, 2, 3
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.
74
Peripherals
Copyright
©
2009
–
2011, Texas Instruments Incorporated
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