Deserial Serial Peripheral Interface (DSPI)
MPC5510 Microcontroller Family Reference Manual, Rev. 1
23-30
Freescale Semiconductor
Preliminary
23.4.1
Modes of Operation
The DSPI modules have four available distinct modes:
•
Master mode
•
Slave mode
•
Module disable mode
•
Debug mode
Master, slave, and module disable modes are module-specific modes, but debug mode is a device-specific
mode.
The module-specific modes are determined by bits in the DSPI
x
_MCR. Debug mode is a mode that the
entire device can enter in parallel with the DSPI being configured in one of its module-specific modes.
23.4.1.1
Master Mode
In master mode the DSPI can initiate communications with peripheral devices. The DSPI operates as bus
master when the MSTR bit in the DSPI
x
_MCR is set. The serial communications clock (SCK) is
controlled by the master DSPI. All three DSPI configurations are valid in master mode.
In SPI configuration, master mode transfer attributes are controlled by the SPI command in the current TX
FIFO entry. The CTAS field in the SPI command selects which of the eight DSPI
x
_CTARs will be used to
set the transfer attributes. Transfer attribute control is on a frame by frame basis. See
“Serial Peripheral Interface (SPI) Configuration
,” for more details.
In DSI configuration, master mode transfer attributes are controlled by the DSPI
x
_DSCIR. A detailed
description of the DSPI
x
Section 23.3.2.10, “DSPI DSI Configuration Register
.” The DSISCTAS field in the DSPI
x
_DSICR selects which of the DSPI
x
_CTARs will be
used to set the transfer attributes. Transfer attributes are set up during initialization and must not be
changed between frames. See
Section 23.4.4, “Deserial Serial Interface (DSI) Configuration
,” for more
details.
The CSI configuration is only available in master mode. In CSI configuration, the DSI data is transferred
using DSI configuration transfer attributes and SPI data is transferred using the SPI configuration transfer
attributes. For the bus slave to distinguish between DSI and SPI frames, the transfer attributes for the two
types of frames must use different peripheral chip select signals. See
Section 23.4.5, “Combined Serial
,” for details.
23.4.1.2
Slave Mode
In slave mode the DSPI responds to transfers initiated by an SPI master. The DSPI operates as bus slave
when the MSTR bit in the DSPI
x
_MCR is negated. The DSPI slave is selected by a bus master by asserting
the slave’s SS. In slave mode, the bus master provides the SCK. All transfer attributes are controlled by
the bus master but clock polarity, clock phase, and numbers of bits to transfer must still be configured in
the DSPI slave for proper communications.
The SPI and DSI configurations are valid in slave mode. CSI configuration is not available in slave mode.
In SPI slave mode the slave transfer attributes are set in the DSPI
x
_CTAR0. In DSI slave mode the slave