RM0046 Fault Collection Unit (FCU)
Doc ID 16912 Rev 5 773/936
After a functional reset, the FCU_FFR (not the Frozen Fault Flag Register (FCU_FFFR))
must be cleared and the FCU must return to Normal state.
28.3.2 Output generation protocol
The FCU provides two external output signals. The FCU supports different protocols for fault
indication to the external device. Both external signals are used only in dual-rail protocol. In
other protocols, the second output is the inverted version of the first output.
In all the protocols, depending on the polarity field (PS) in the MCR, the outputs can be
normal polarity (if PS = 0) or inverted polarity (if PS = 1). The LSB of PS sets the polarity of
the first signal; the MSB sets the polarity of the second signal.
Dual-rail protocol
Dual-rail encoding is an alternate method for encoding bits. In contrast to classical
encoding, where each wire carries a single bit-value, dual-rail encoded circuits use two
wires to carry each bit. Table 4 1 2 summarizes the encoding.
As long as the FCU is in Normal or Alarm state, the output shows a “non-faulty” signal.
FCU[0], FCU[1] toggles between (0,1) and (1,0) with a given frequency, set in the FOP field
of the MCR. By default, this value is f = 976 Hz @ 64 MHz (about 1 kHz, see Equation 34).
The same frequency is used to show a faulty situation (FCU in Fault state).
In the Init state, output pins are set as high impedance by clearing the OBE bits for each pad
in its respective PCR in the SIUL module.
Table 412. Dual-rail coding
Logical value Dual-rail encoding (FCU[0], FCU[1])
non-faulty (0,1)
non-faulty (1,0)
faulty (0,0)
faulty (1,1)
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