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MC68F375
QUEUED SERIAL MULTI-CHANNEL MODULE
MOTOROLA
REFERENCE MANUAL
Rev. 25 June 03
6-41
mands are executed again. SPE is not cleared by the QSPI. New receive data
overwrites previously received data located in the receive data segment.
Wraparound mode is properly exited in two ways: a) The CPU may disable wrap-
around mode by clearing WREN. The next time end of the queue is reached, the QSPI
sets SPIF, clears SPE, and stops; and, b) The CPU sets HALT. This second method
halts the QSPI after the current transfer is completed, allowing the CPU to negate
SPE. The CPU can immediately stop the QSPI by clearing SPE; however, this method
is not recommended, as it causes the QSPI to abort a serial transfer in process.
6.7.8 Mode Fault
MODF is asserted by the QSPI when the QSPI is the serial master (MSTR = 1) and
the slave select (PCS0/SS) input pin is pulled low by an external driver. This is possi-
ble only if the PCS0/SS pin is configured as input by QDDR. This low input to SS is not
a normal operating condition. It indicates that a multimaster system conflict may exist,
that another MCU is requesting to become the SPI network master, or simply that the
hardware is incorrectly affecting PCS0/SS. SPE in SPCR1 is cleared, disabling the
QSPI. The QSPI pins revert to control by QPDR. If MODF is set and HMIE in SPCR3
is asserted, the QSPI generates an interrupt to the CPU.
The CPU may clear MODF by reading SPSR with MODF asserted, followed by writing
SPSR with a zero in MODF. After correcting the mode fault problem, the QSPI can be
re-enabled by asserting SPE.
The PCS0/SS pin may be configured as a general-purpose output instead of input to
the QSPI. This inhibits the mode fault checking function. In this case, MODF is not
used by the QSPI.
6.8 Serial Communication Interface
The dual, independent, serial communication interface (DSCI) communicates with
external devices through an asynchronous serial bus. The two SCI modules are func-
tionally equivalent, except that the SCI1 also provides 16-deep queue capabilities for
the transmit and receive operations. The SCIs are fully compatible with other Motorola
SCI systems. The DSCI has all of the capabilities of previous SCI systems as well as
several significant new features.
of the SCI receiver.
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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