35.5.9.1 SS OutputThe SS output feature automatically drives the SS pin low during transmission to selectexternal devices and drives the SS pin high during idle to deselect external devices. Whenthe SS output is selected, the SS output pin is connected to the SS input pin of theexternal device.The SS output is available only in master mode during normal SPI operation by assertingC1[SSOE] and C2[MODFEN] as shown in the description of C1[SSOE].The mode fault feature is disabled while SS output is enabled.NoteBe careful when using the SS output feature in a multimastersystem because the mode fault feature is not available fordetecting system errors between masters.35.5.9.2 Bidirectional mode (MOMI or SISO)The bidirectional mode is selected when the SPC0 bit is set in SPI Control Register 2 (seethe following table). In this mode, the SPI uses only one serial data pin for the interfacewith one or more external devices. C1[MSTR] decides which pin to use. The MOSI pinbecomes the serial data I/O (MOMI) pin for the master mode, and the MISO pin becomesserial data I/O (SISO) pin for the slave mode. The MISO pin in master mode and MOSIpin in slave mode are not used by the SPI.Table 35-2. Normal Mode and Bidirectional ModeWhen SPE = 1 Master Mode MSTR = 1 Slave Mode MSTR = 0Normal ModeSPC0 = 0MOSIMISOSerial OutSPISerial InMOSIMISOSerial OutSPISerial InBidirectional ModeSPC0 = 1Serial OutSPISerial InMOMIBIDIROESerial OutSPISerial InSISOBIDIROEThe direction of each serial I/O pin depends on C2[BIDIROE]. If the pin is configured asan output, serial data from the shift register is driven out on the pin. The same pin is alsothe serial input to the shift register.The SPSCK is an output for the master mode and an input for the slave mode.Chapter 35 Serial Peripheral Interface (SPI)KL27 Sub-Family Reference Manual , Rev. 5, 01/2016Freescale Semiconductor, Inc. 599
