ST STM32F446 Series Reference Manual page 902

SPDIF receiver interface (SPDIFRX)
The search of the longest and shortest transition is stopped when the transition timer
expires. The transition timer is like a watchdog timer that generates a trigger after 70
transitions of the incoming signal. Note that counting 70 transitions insures a delay a bit
longer than a sub-frame.
Note that when the TRCNT overflows due to a too long time interval between two pulses,
the SPDIFRX is stopped and the flag TERR of SPDIFRX_SR register is set to 1.
Transition coder and preamble detector
The transition coder and preamble detector block receives the MAX_CNT and
MIN_CNT. It also receives the current transition width from the TRCNT counter (see
Figure 343). This block encodes the current transition width by comparing the current
transition width with two different thresholds, names TH
•
If the current transition width is less than (TH
of data bit '1', and is coded as TS.
•
If the current transition width is greater than (TH
data received is data bit '0', and is coded as TM.
•
If the current transition width is greater than TH
pulse of preambles, and is coded as TL.
•
Else an error code is generated (FERR flag is set).
The thresholds TH
If the peripheral is doing its initial synchronization ('coarse synchronization'), then the
thresholds are computed as follow:
•
TH
LO
•
TH
HI
Once the 'coarse synchronization' is completed, then the SPDIFRX uses a more accurate
reference in order to elaborate the thresholds. The SPDIFRX measures the length of 24
symbols (WIDTH24) for defining TH
TH and TH
HI
• TH
LO
•
TH
HI
This second synchronization phase is called the 'fine synchronization'. Refer to
for additional information.
As shown in the figure hereafter, TH
902/1328
and TH are elaborated using two different methods.
HI LO
= MAX_CNT / 2.
= MIN_CNT + MAX_CNT / 2.
are computed as follow:
LO
= (WIDTH24) / 32
= (WIDTH40) / 32
- 1), then the data received is half part
LO
LO
, then the data received is the long
HI
and the length of 40 symbols (WIDTH40) for TH
LO
is ideally equal to 1.5 UI, and to TH
LO
RM0390 Rev 4
and TH .
HI LO
- 1), and less than TH
HI
RM0390
, then the
HI
.
HI
Figure 347
2.5 UI.