SYNCHRONOUS SERIAL INTERFACE (SSI)
MOTOROLA
PORT C
6 - 95
Data written to the transmit data register during the time slot when TFS is set will be transmit-
ted (in network mode) during the second time slot in the frame. TFS is useful in network mode
to identify the start of the frame. This is illustrated in a typical transmit interrupt handler:
MOVEP
X:(R4)+,X:SSITx
JCLR
#2,X:SSISR,_NoTFS;1 = FIRST TIMESLOT
;Do something
JMP
_DONE
_NoTFS
;Do something else
_DONE
Note: In normal mode, TFS will always read as a one when transmitting data because
there is only one time slot per frame – the “frame sync” time slot.
TFS, which is cleared by hardware, software, SSI individual, or STOP reset, is not
affected by TE.
6.4.2.3.4
SSISR Receive Frame Sync Flag (RFS) Bit 3
When set, RFS indicates that a receive frame sync occurred during reception of the word
in the serial receive data register. This indicates that the data word is from the first time
slot in the frame. If word-wide receive frame sync is selected (FSL1=0), this indicates that
the frame sync was high at least at the beginning of the timeslot. If bit-wide receive frame
sync is selected (FSL1=1), this indicates that the frame sync (either internal or external)
was high during the last bit period prior to the current timeslot, and that the frame sync
falling edge corresponds to the assertion of the first output data bit, as shown below.
When RFS is clear and a word is received, it indicates (only in network mode) that the
frame sync did not occur during reception of that word. RFS is useful in network mode to
identify the start of the frame. This feature is illustrated in a typical receive interrupt handler:
Time slot #1
Time slot #2
Time slot #3
RFS set here
Bit-Length Fs
Word-Length Fs
Rx shift clock
Time slots
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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