SPRS439I – JUNE 2007 – REVISED MARCH 2011
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4.11 Serial Peripheral Interface (SPI) Module (SPI-A )
The device includes the four-pin serial peripheral interface (SPI) module. One SPI module (SPI-A) is
available. 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 DSC 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
=
LSPCLK
(SPIBRR
+
1)
LSPCLK
4
when SPIBRR
=
3 to 127
Baud rate
=
when SPIBRR
=
0, 1, 2
NOTE
See
for maximum I/O pin toggling speed.
•
•
•
•
•
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.
96
Peripherals
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