19.4.1.1 SPI Host Mode Clock Frequency

The SPI module allows flexibility in baud rate generation through the 13-bit SPIxBRG register. SPIxBRG is readable and writable and determines the baud rate. The clock provided to the SPI module, FSPICLK, can be found in Table 19-2. This clock is divided based on the value loaded into SPIxBRG. The SCKx clock, obtained by dividing F_SPICLK, is 50% duty cycle and it is provided to the external devices through the SCKx pin. Refer to Figure 19-29.

Note: The SCKx clock is not free running for Non-Framed SPI modes. It will only run for 8, 16 or 32 pulses when SPIxBUF is loaded with data. It will, however, be continuous for Framed modes.

Equation 19-1 defines the SCKx clock frequency as a function of SPIxBRG settings.

Therefore, the maximum baud rate possible is F_SPICLK/2 (SPIxBRG = 0) and the minimum baud rate possible is F_SPICLK/16384.

Some sample SPI clock frequencies are shown in Table 19-13.

Table 19-13. Sample SCKx Frequencies⁽¹⁾
SPIxBRG Setting	0	15	31	63	85	127	255	511
F_SPICLK = 32 MHz	16.00 MHz	10.0 MHz	500 kHz	257 kHz	190.48 kHz	125 kHz	62.5 kHz	31.25 kHz
F_SPICLK = 25 MHz	12.50 MHz	781.25 kHz	390.63 kHz	145.35 kHz	97.66 kHz	281.25 kHz	48.83 kHz	24.41 kHz
F_SPICLK = 20 MHz	10.00 MHz	625 kHz	312.50 kHz	156.25 kHz	116.28 kHz	78.13 kHz	39.06 kHz	19.53 kHz
F_SPICLK = 12 MHz	6.00 MHz	375 MHz	187.50 kHz	93.75 kHz	69.77 kHz	46.88 kHz	23.44 kHz	11.72 kHz
F_SPICLK = 10 MHz	5.00 MHz	312.50 kHz	156.25 kHz	78.13 kHz	58.14 kHz	39.06 kHz	19.53 kHz	9.77kHz
F_SPICLK = 8 MHz	4.00 MHz	250 kHz	125 kHz	62.50 kHz	46.51 kHz	31.25 kHz	15.63 kHz	7.81 kHz
Note: Not all clock rates are supported. For further information, refer to the SPI timing specifications in the Electrical Characteristics.