NXP Semiconductors KL25 Series - Freescale Semiconductor, Inc

37.1.3.2 SPI Module Block Diagram
The following is a block diagram of the SPI module. The central element of the SPI is the
SPI shift register. Data is written to the double-buffered transmitter (write to SPIx_D) and
gets transferred to the SPI shift register at the start of a data transfer. After shifting in 8
bits of data, the data is transferred into the double-buffered receiver where it can be read
from SPIx_D. Pin multiplexing logic controls connections between MCU pins and the
SPI module.
When the SPI is configured as a master, the clock output is routed to the SPSCK pin, the
shifter output is routed to MOSI, and the shifter input is routed from the MISO pin.
When the SPI is configured as a slave, the SPSCK pin is routed to the clock input of the
SPI, the shifter output is routed to MISO, and the shifter input is routed from the MOSI
pin.
In the external SPI system, simply connect all SPSCK pins to each other, all MISO pins
together, and all MOSI pins together. Peripheral devices often use slightly different
names for these pins.
Introduction
KL25 Sub-Family Reference Manual, Rev. 3, September 2012
658 Freescale Semiconductor, Inc.