• SPSCK• The SPR3, SPR2, SPR1, and SPR0 baud rate selection bits in conjunction withthe SPPR2, SPPR1, and SPPR0 baud rate preselection bits in the SPI Baud Rateregister control the baud rate generator and determine the speed of thetransmission. The SPSCK pin is the SPI clock output. Through the SPSCK pin,the baud rate generator of the master controls the shift register of the slaveperipheral.• MOSI, MISO pin• In master mode, the function of the serial data output pin (MOSI) and the serialdata input pin (MISO) is determined by the SPC0 and BIDIROE control bits.• SS pin• If C2[MODFEN] and C1[SSOE] are set, the SS pin is configured as slave selectoutput. The SS output becomes low during each transmission and is high whenthe SPI is in idle state. If C2[MODFEN] is set and C1[SSOE] is cleared, the SSpin is configured as input for detecting mode fault error. If the SS input becomeslow this indicates a mode fault error where another master tries to drive theMOSI and SPSCK lines. In this case, the SPI immediately switches to slavemode by clearing C1[MSTR] and also disables the slave output buffer MISO (orSISO in bidirectional mode). As a result, all outputs are disabled, and SPSCK,MOSI and MISO are inputs. If a transmission is in progress when the mode faultoccurs, the transmission is aborted and the SPI is forced into idle state. Thismode fault error also sets the Mode Fault (MODF) flag in the SPI Status Register(SPIx_S). If the SPI Interrupt Enable bit (SPIE) is set when S[ MODF] gets set,then an SPI interrupt sequence is also requested. When a write to the SPI DataRegister in the master occurs, there is a half SPSCK-cycle delay. After the delay,SPSCK is started within the master. The rest of the transfer operation differsslightly, depending on the clock format specified by the SPI clock phase bit,CPHA, in SPI Control Register 1 (see SPI clock formats).NoteA change of C1[CPOL], C1[CPHA], C1[SSOE], C1[LSBFE],C2[MODFEN], C2[SPC0], C2[BIDIROE] with C2[SPC0] set,SPIMODE, FIFOMODE, SPPR2-SPPR0 and SPR3-SPR0 inmaster mode abort a transmission in progress and force the SPIinto idle state. The remote slave cannot detect this, therefore themaster has to ensure that the remote slave is set back to idlestate.Chapter 35 Serial Peripheral Interface (SPI)KL27 Sub-Family Reference Manual , Rev. 5, 01/2016Freescale Semiconductor, Inc. 589
