MC1321x Serial Peripheral Interface (SPI)
MC1321x Reference Manual, Rev. 1.6
4-6
Freescale Semiconductor
4.6
MCU SPI Block Diagrams
This section includes block diagrams showing the internal organization of the SPI module and the SPI
clock dividers that control the Master Mode bit rate.
4.6.1
MCU SPI Module Block Diagram
is a block diagram of the SPI module.
Figure 4-4. MCU SPI Module Block Diagram
The central element of the SPI is the SPI shift register. Data is written to the double-buffered transmitter
(write to SPI1D) and gets transferred to the SPI shift register at the start of a data transfer. After shifting
in a byte of data, the data is transferred into the double-buffered receiver where it can be read (read from
SPI1D). 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 SPSCK1 pin, the shifter output is
routed to MOSI1, and the shifter input is routed from the MISO1 pin.
When the SPI is configured as a slave, the SPSCK1 pin is routed to the clock input of the SPI, the shifter
output is routed to MISO1, and the shifter input is routed from the MOSI1 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.
SPI SHIFT REGISTER
SHIFT
CLOCK
SHIFT
DIRECTION
Rx BUFFER
FULL
Tx BUFFER
EMPTY
SHIFT
OUT
SHIFT
IN
ENABLE
SPI SYSTEM
CLOCK
LOGIC
CLOCK GENERATOR
US RATE
CLOCK
MASTER/SLAVE
MODE SELECT
MODE FAULT
DETECTION
MASTER CLOCK
SLAVE CLOCK
SPI
INTERRUPT
REQUEST
PIN CONTROL
M
S
MASTER/
SLAVE
MOSI1
(MOMI)
MISO1
(SISO)
SPSCK1
SS1
M
S
S
M
MODF
SPE
LSBFE
MSTR
SPRF
SPTEF
SPTIE
SPIE
MOD-
SSOE
SPC0
BID-
SPIBR
Tx BUFFER
Rx BUFFER
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