The serial peripheral interface (SPI) is a high-speed synchronous serial input and output (I/O) port that allows a serial bit stream of programmed length (1 to 16 bits) to be shifted into and out of the device at a programmed bit-transfer rate. The SPI is normally used for communications between the MCU controller and external peripherals or another controller. Typical applications include external I/O or peripheral expansion through devices such as shift registers, display drivers, and analog-to-digital converters (ADCs). Multidevice communications are supported by the controller or peripheral operation of the SPI. The port supports a 16-level, receive and transmit FIFO for reducing CPU servicing overhead.

The SPI module features include:

• SPIPOCI: SPI peripheral-output/controller-input pin
• SPIPICO: SPI peripheral-input/controller-output pin
• SPIPTE: SPI peripheral transmit-enable pin
• SPICLK: SPI serial-clock pin
• Two operational modes: Controller and Peripheral
• Baud rate: 125 different programmable rates. The maximum baud rate that can be employed is limited by the maximum speed of the I/O buffers used on the SPI pins.
• Data word length: 1 to 16 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 rising 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 algorithm
• 16-level transmit/receive FIFO
• High-speed mode
• Delayed transmit control
• 3-wire SPI mode
• SPIPTE inversion for digital audio interface receive mode on devices with two SPI modules

Figure 6-96 shows the SPI CPU interfaces.

Figure 6-96 SPI CPU Interface