PXR40RM Datasheet, PDF (276/1434 Pages) Freescale Semiconductor, Inc – PXR40 Microcontroller

System Integration Unit (SIU)
In a serial chain, one DSPI module operates as a master, the second, third, or fourth DSPI modules operates
as aslaves.The slave DSPI and external SPI device use the master peripheral chip select (PCS) and clock
(SCK). The trigger input of the master allows a slave DSPI to trigger a transfer when a data change occurs
in the slave DSPI and the slave DSPI is operating in change in data mode. The trigger input of the master
is connected to the MTRIG output of the slave. If more than two DSPIs are chained in change in data mode,
a chain must be connected of MTRIG outputs to trigger inputs through the slaves with the last slave
MTRIG output connected to the master trigger input.
An example of a serial chain is shown in Figure 7-52.
Parallel chaining allows the PCS and SCK from one DSPI to be used by more than one external SPI device,
thus reducing pin utilization of the device MCU. In this example, the SOUT and SIN of the two DSPIs
connect to separate external SPI devices, which share a common PCS and SCK.
To support multiple transfer operation of the DSPIs, an input multiplexor is required for the SIN, SS, SCK
IN, and trigger signals of each DSPI. The input source for the SIN input of a DSPI can be a pin or the
SOUT of any of the other three DSPIs. The input source for the SS input of a DSPI can be a pin or the
PCSX[0] of any of the other three DSPIs. The input source for the SCK input of a DSPI can be a pin or the
SCK output of any of the other three DSPIs. The input source for the trigger input can be the PCSS output
of any of the other three DSPIs. The input source for each DSPI SIN, SS, SCK, and trigger signal is
individually specified in the DSPI input select register (SIU_DISR).
An example of a parallel chain is shown in Figure 7-53.
DSPI B (master)
DSPI C (slave)
SIN
SOUT
Trigger
PCS[0]
SCK
SIN
MTRIG
SOUT
SS
SCK IN
SS
SCK IN
SOUT
External SPI device
SIN
Figure 7-52. DSPI Serial Chaining
7-94
PXR40 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor