The device supports frame and multiframe monitoring for verifying the health of the JESD204C link when using 8B/10B encoding. The scheme changes depending on the use of scrambling. The implementation when scrambling is disabled is covered first. If the last octet of the current frame matches the last octet of the previous frame, then the last octet of the current frame is encoded as an /F/ (K28.7) character. If the current frame is also the last frame of a multiframe, then an /A/ (K28.3) character is used instead. Neither an /F/ or /A/ character should occur in a normal data stream, except when replaced by the transmitter for alignment monitoring. When the receiver detects an /F/ or /A/ character in the normal data stream the receiver checks to see if the character occurs at the location expected to be the end of a frame or multiframe. If the character occurs at a location other than the end of a frame or multiframe then either the transmitter or receiver has become misaligned. The receiver replaces the alignment character with the appropriate data character upon reception of a properly aligned /F/ or /A/ character. The appropriate data character is the last octet of the previously received frame. This scheme increases the probability of an alignment character for non-scrambled data streams.

The implementation when scrambling is enabled is slightly different since the octets are randomized. If the last octet of a frame is 0xFC (before 8B/10B encoding) then the transmitter encodes the octet as an /F/ (/K28.7/) character. If the last octet of a multiframe is 0x7C (before 8B/10B encoding) then the transmitter encodes the octet as an /A/ (/K28.3/) character. The location of the /A/ and /F/ characters is monitored to verify proper frame and multiframe alignment. The receiver replaces the alignment characters by simply replacing an /F/ character with the 0xFC octet and an /A/ character with the 0x7C octet.

The receiver can report an error if multiple alignment characters occur in the incorrect location or do not occur when expected. Upon detection of a frame or multiframe misalignment, the receiver should trigger a link realignment by asserting SYNC. SYSREF should also be reissued to verify that the LMFC in the transmitter and receiver have proper alignment before restarting the link.