ST STM32F423 Reference Manual page 400

Digital filter for sigma delta modulators (DFSDM)
Manchester/SPI code synchronization
The Manchester coded stream must be synchronized the first time after enabling the
channel (CHEN=1 in DFSDM_CHyCFGR1 register). The synchronization ends when a data
transition from 0 to 1 or from 1 to 0 (to be able to detect valid data edge) is received. The
end of the synchronization can be checked by polling CKABF[y]=0 for a given channel after
it has been cleared by CLRCKABF[y] in DFSDM_FLT0ICR, following the software sequence
detailed hereafter:
CKABF[y] flag is cleared by setting CLRCKABF[y] bit. If channel y is not yet synchronized
the hardware immediately set the CKABF[y] flag. Software is then reading back the
CKABF[y] flag and if it is set then perform again clearing of this flag by setting
CLRCKABF[y] bit. This software sequence (polling of CKABF[y] flag) continues until
CKABF[y] flag is set (signalizing that Manchester stream is synchronized). To be able to
synchronize/receive Manchester coded data the CKOUTDIV divider (in
DFSDM_CH0CFGR1 register) must be set with respect to expected Manchester data rate
according the formula below.
( (
SPI coded stream is synchronized after first detection of clock input signal (valid
rising/falling edge).
Note: When the transceiver is not yet synchronized, the clock absence flag is set and cannot be
cleared by CLRCKABF[y] bit (in DFSDM_FLT0ICR register).
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) ×
CKOUTDIV 1 T
+
SYSCLK
) T < < (
Manchester clock
RM0430 Rev 8
× ×
2 CKOUTDIV T
SYSCLK
RM0430
)