MPC5553/MPC5554 Microcontroller Reference Manual, Rev. 5
20-40
Freescale Semiconductor
Figure 20-20. DSI Deserialization Diagram
20.4.4.5
DSI Transfer Initiation Control
Data transfers for a master DSPI in DSI configuration are initiated by a condition. When chaining DSPIs,
the master and all slaves must be configured for the transfer initiation. The transfer initiation conditions
are selected by the TRRE and CID bits in the DSPI
x
_DSICR.
lists the four transfer initiation
conditions.
20.4.4.5.1
Continuous Control
For continuous control, the initiation of a transfer is based on the baud rate at which data is transferred
between the DSPI and the external device. The baud rate is set in the DSPI
x
_CTAR selected by the
DSICTAS field in the DSPI
x
_DSICR. A new DSI frame shifts out when the previous transfer cycle has
completed and the delay after transfer (t
DT
) has elapsed.
20.4.4.5.2
Change In Data Control
For change in data control, a transfer is initiated when the data to be serialized has changed since the
transfer of the last DSI frame. A copy of the previously transferred DSI data is stored in the
DSPI
x
_COMPR. When the data in the DSPI
x
_SDR or the DSPI
x
_ASDR is different from the data in the
DSPI
x
_COMPR, a new DSI frame is transmitted. The TXSS bit in the DSPI
x
_DSICR selects which
register the DSPI
x
_COMPR is compared to. The MTRIG output signal is asserted every time a change in
data is detected.
20.4.4.5.3
Triggered Control
For triggered control, initiation of a transfer is controlled by the internal hardware trigger signal (
ht
). The
TPOL bit in the DSPI
x
_DSICR selects the active edge of
ht
. For
ht
to have any affect, the TRRE bit in the
DSPI
x
_DSICR must be set.
Table 20-18. DSI Data Transfer Initiation Control
DSPIx_DSICR Bits
TRRE
CID
Type of Transfer Initiation Control
0
0
Continuous
0
1
Change in Data
1
0
Triggered
1
1
Triggered or Change in Data
SIN
Control
Logic
0 1 • • • • • 15
Shift Register
16
Slave Bus Interface
Parallel
DSI Deserialization
Data Register
Outputs
16
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