In the JESD204C RX core, the SYNC~ signal can be deasserted for two frame periods at the end of each multiframe to indicate an error has occurred which does not require a full reinitialization of the link. This behavior is enabled by the deassertion of the disable_error_reporting control bit.
The SYNC~ signal is a 1-bit output; this enables the correct error output for a frame size of down to two octets. The signal is Low when the receiver has detected an error. An error occurs when an idle or an unexpected control character is received during normal frame transmission.
To give a frame-accurate SYNC~ output when the frame size is one octet, the SYNC~ signal should be asserted for only half a cycle of the device clock. This is not implemented in the core as it would require a dedicated clock (either twice the device clock speed or an inverted device clock). If accurate timing of SYNC~ assertion for error reporting is required, logic must be added externally to generate a half cycle pulse on the external SYNC~ pin if the core SYNC~ signal is asserted for a single cycle and F = 0.